organo-sulfur phosphorus chemistry · thanks to paul, jon parr, maria, marek, spanner, john...
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Organo-sulfur phosphoruschemistry
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Author/Filing Title ............. ~.~ . .) ..... I':':1 .. ,R:.S.., ....... .
Accession/Copy No.
Vol. No ............... ..
25 JUN 199
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Class Mark ' . ....................... . .......................
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7'
Organo Sulfur Phosphorus Chemistry
by
Mark Russell StJohn Foreman
A Doctoral Thesis
Submitted in partial fulfilment of the requirements for the award of
Doctor of Philosophy of Loughborough University . . .
April 1998
<Cl by Mark R. StJ. Foreman 1998 .
" . .. . ' . .I
Abstract
P-organo substituted dithiadiphosphetane disulfides have been prepared by the reaction
of ferrocene and arenes with P 4S,O. Reaction of these compounds and Lawesson's
reagent with alkenes, 2,3-dimethylbutadiene and other compounds gave organo sulfur
phosphorus compounds including 1,2-thiaphosphetane-2-sulfides such as P-ferrocenyl
1 ,2,5,S, 7,8-hexamethyltricyclo[3,2:·20]-3-thia-4-phospho-oct-7 -ene-4-sulfide and a
thiaphosphorine sulfide (P-ferrocenyl 4,5-dimethyl-3H,SH-1,2-thiaphosphinine-2-sulfide).
Treatment of P-ferrocenyl thiaphosphorine sulfide with BuLi followed by carbon containing
electrophiles (Such as benzyl bromide or 2,4-dinitrochlorobenzene) gave ring opened
products. In addition treatment of dithiadiphosphetane disulfides with organic carbonyl
compounds, including ketones, gave thiocarbonyl compounds. Platinum complexes were
formed from the dithiadiphosphetane disulfides.
Treatment of dithiadiphosphetane disulfides with dialkyl cyanamides yielded a mixture of
nitrogen phosphorus sulfur compounds (Including P-isothiocyantes). Treatment of imines
and dicyclohexyl carbodiimide with a dithiadiphosphetane gave a mixture of different
products which include thiazadiphosphetane disulfides. The reaction of N-benzylidene
benzyl amine with diferrocenyl dithiadiphosphetane disulfide furnished P-ferrocenyl 4,5-
diphenyl-1,3,2-dithiaphospholane-2-sulfide, which is believed to have been formed via
thiobenzaldehyde. The thiobenzaldehyde was formed in situ.
The reaction of catechols with dithiadiphosphetane disulfides gave oxygen containing ring
compounds. The ring forming chemistry was seen to change on alteration of the
dithiadiphosphetane disulfide to a napthalen-1,8-diyl substituted compound.
Compounds which were prepared for the first time were characterised by means of IR '.I.~~ •• _.'~ ... ",,\~·~ ......... ~ •. ,
spectroscopy, mass spectroscopy; multiJ]uClleaq'IM~:>spectroscopy, and microanalysis. In . ". . . -, .,' .:::-.!.'! .,~, ?: ~".~;
selected cases the compounds were siudiecliby: single crystal X-ray crystallography and ~ .:/
by electrochemical means .. : ..
..:,-: .. - . . .....
. . . .. """"~'" -"","',.
2
Chapter 1
Chapter 2
Chapter 3
Chapter 4
Chapter 5
Chapter 6
Chapter 7
References
Contents
The synthesis of new dithiadiphosphetane disulfides by the reaction
of arenes with P 45'0
Metal complexes from diferrocenyl dithiadiphosphetane disulfide
Thionation of organic compounds
The reactions of dithiadiphosphetane disulphide with catechols
The reaction of dithiadiphosphetane disulfides with dienes,
alkenes and thiobenzaldehyde
Reactions of dithiadiphosphetane disulfides with
organonitrogen compounds
Electrochemical characterization.
Crystal Structure Data
8
31
42
65
83
139
202
207
214
3
Acknowledgements
My greatest thanks must go out towards Prof. J. Derek Woollins for his unending
enthusiasm for chemistry and his regular and lively advice on a range of topics including
(but not limited to) cars, cats, motor bikes, student behaviour, relationships, men's
fashions and chemistry. To Alex Slawin thanks for all the crystallography, advice on
crystal growth, humour, and updates on the condition and behaviour of the two lifeforms
known as Sammy and Buster (the cats). Special thanks to Josef Novosad for his advice
and enthusiasm on phosphorus sulfur chemistry, and thanks to his research student Petr.
Thanks to Pauline King for all her help, in particular the CHN elemental analysis. Thanks
to Astra Charnwood for their generous gift of the CHNS analysis work.
To my grandparents, parents, James, Juliet, Derek, Jon (Clockman), Matt, Roger, Bev,
Alex and Andrew my best wishes and do take good care of yourselves. Derek and Jon, to
Tock or not to Tock which is more noble. Thanks to the people I know from the Linford.
Thanks to David Heart and the AngSoc people, you are too many to thank you all by
name. Ed try to lose that baseball cap even if Nicki told you to wear it.
Thanks to Paul, Jon Parr, Maria, Marek, Spanner, John Halburn, Rob (golfman), Tuan,
Toni, Rob, Steve, Pauline, Pravat, Dave and 'Gabbi'. Thanks a bundle for the Catherine
wheels! Thanks to Roger Mortimer, and his research group, for all the help and training in
cyclic voltammetry that he has given me. Also Roger, thanks for the help with the pulsed
methods. Thanks to Linda Sands and the John for the El mass spec, and thanks to the
EPSRC mass spec service at Swansea. Thanks to John and Graham from the NMR
room. Thanks to all the people who work to support and maintain the Bath Information
Directory Service (BIDS), Beilstein/Gmelin Crossfire system, and the other on-line search
systems which I have used. Thanks to Dave Wilson for sounding the lunch bell every
Friday, and his help with GPC. Special thanks to Pravat, Ron Hinton and Mona-Lisa
Cooke for making sense of that, which I could not.
Special thanks to Andy and John Booth for extensive technical support with all things
computerised, are you going to create an entire microprocessor controlled hall of
residence room? Best wishes to Albert and Andy (the tetrode men), Don (4X150 man),
'Art' and Co, carry on valved home brew! Good luck to lan (Zap man) and all the other
members. Remember lads, Tetrode Power rules OK ! While we have had our ups and
downs with rigs, hopefully the kit will not rebel too often ! lan is true what you said about
TV repair work being like club 18-30? HT, OX, chips and gravy !
4
A
1-Adm
An
AI20 3
Ar
Bn
'-BOC
Bu
;-Bu
'-Bu
BuLi
Bu.N+
brs
CDCI3
CIO;
cm-'
Cp
CV
d
8
Il.
dppe
DCC
DMSO
El
ES
Et
List of Abbreviations
Angstrom, 100 pm (10-10 m).
1-Adamantyl
para-Methoxyphenyl (anisyl)
Active alumina for chromatography
Aromatic group
Benzyl
Me3COCO- group
Butyl
, isobutyl
tert-Butyl
Butyl lithium
Tetrabutyl ammonium
Broad singlet
Deutro-chloroform
Perchlorate
wavenumber
cyclopentadienyl group
Cyclic voltammetry
Doublet
Chemical shift
Heating
Ph2PCH2CH2PPh2
Dicyclohexyl carbodimide
Dimethyl sulfoxide
Electron impact
Electro spray
Ethyl
5
FAB Fast atom bombardment
Fc Ferrocenyl
Fc2P2S4 2,4-Diferrocenyll ,3,2,4-dithiadiphosphetane 2,4-disulfide
FT Fourier transform (for NMR or IR)
GCMS Gas chromatography mass spectrometry
GPC Gel permeation chromatography
HOMO Highest occupied molecular orbital
HPLC High pressure liquid chromatography
HRMS High resolution mass spectrometry.
HSAB Hard, Soft Acids and Bases.
hv Action of light (can be UV or visible)
IR Infra Red
J Coupling constant, Hz.
K Kelvin
LR Lawesson's reagent (bis-(4-methoxyphenyl) dithiadiphosphetane disulfide)
LW Bis-(3-'-bulyl-4-methoxyphenyl) dithiadiphosphetane disulfide
LUMO Lowest unoccupied molecular orbital
m Multiplet
m Medium (IR)
m/z (or m/q) Mass to charge ratio.
Me Methyl
MeCN Acetonitrile
MS Mass spectrometry
Ne Neopenlyl
NMR Nuclear Magnetic Resonance
l-Np l-Napthyl
2-Np 2-Napthyl
Ph Phenyl
pip Piperidinyl
6
ppm
Pr
q
quat
R
s
s
sh
Si02
THF
TLC
TMS
vs
w
w.r. to
z
Parts per million
Propyl
Iso-propyl
quartet
quaternary
Alkyl or aryl group
Singlet (NMR)
Strong (IR)
shoulder (IR)
Flash column silica.
Tetrahydrofuran
Thin layer chromatography
eitherTetramethylsilane (internal standard for 'H and 13C NMR) or Trimethylsilyl group
Very strong (IR)
Weak
With respect to
Benzyloxycarbonyl group (protecting group in peptide chemistry)
7
Chapter 1
The Synthesis of New Dithiadiphosphetane Disulfides by
the Reaction of Arenes with P 4S10
Section 1.1 Introduction.
Lawesson's reagent (LR) (2,4-bis(4-methoxyphenyl) 1,3,2,4-dithiadiphosphetane 2,4-
disulfide) has a rich and diverse chemistry. This introduction provides an overview of the
synthesis of LR. The majority of heterocyclic compounds were named using the
Hantzsch-Widman system.'
The synthesis of LR (op 15 ppm)2 proceeds by an electrophilic aromatic substitution
reaction of P ,SIO with anisole (1). A variety of different arenes and alkenes have been
reacted with P ,SIO to give dithiadiphosphetane disulfides - in this mechanism electron rich
aromatic compounds react more readily than electron poor compounds (Equation 1.1 and
Table 1.1).
4ArH
S Ar __ p"_s
P,S,o -'--"i~~ I I
Il. S-P--Ar If S
Equation 1. 1.
Table 1.1 SyntheSiS of dithiadiphosphetane disulfides from P ,SIO'
Arene/Alkenere' Yield Conditions
(%)
Anisole (1 )3 80 6 h heating under reflux
Phenetole3 63 5 h at 165'C
Naphthalene3 37 24 h at 170-180'C
Benzene3 45 Autoclave at 225'C for 24 h
o-Xylene3 488 Autoclave at 185'C for 24 h
2-lsopropylnaphthalene3 11 a 8 h at 170-175'C
Cyclohexene' 58 108 h heating under reflux
Ph20S 75 25 minutes heating under reflux in o-dichlorobenzene
Ph2SS 65 25 minutes heating under reflux in o-dichlorobenzene
Thiophene· 87 Heat under reflux
8 Yield of the P-organophosphonic acid.
8
A number of other alkoxybenzenes have been reacted with P,S,o to give
dithiadiphosphetane disulfides. Many of the products are more soluble than LR and were
intended for use in room temperature thionation reactions.'
A related reaction is that of arenes with P20 S and after treatment with water phosphinic
acids are obtained (equation 1.2)8
¥ ..
R
o 11
HO-P-OH
o R
Equation 1.2.
(R = H, Cl)
Alternatively naphthalene can be used as the arene, giving as the final product 2-naphthyl
phosphinic acid
The synthesis of 2,4-(naphthalen-1,8-diyl) 1,3,2,4-dithiadiphosphetane 2,4-disulfide
(NpP2S,) [op 16 ppm. v(P=S)=670 cm"] from P,S,o and 1-bromonaphthalene (2) has
been reported· Prior to this work the full synthesis of this compound had not been
described. Whilst the formation of dithiadiphosphetane disulfides (such as LR from 1)
from arenes proceeds via aromatic electrophilic substitution, the formation of NpP2S,
occurs via an unknown mechanism. The rate determining step for the reaction of P ,S,o
with 2 is likely to be the formation of a reactive free radical intermediate from the 1-
halo naphthalene (Scheme 1.1).
Br
Slow Fast .. ..
Scheme 1.1 Synthesis of NpP2S4 .
The reaction of P ,SlO with naphthalene (3) gives a mixture of NpP2S4 and
dithiadiphosphetane disulfides with a.-naphthyl and ~-naphthyl groups attached to the
phosphorus atoms· The rate determining step for the reaction of 3 with P,S,o is probably
the attack of the phosphorus sulfide on the aromatic ring. Since 3 is at such a high
concentration and since it can react in two positions the formation of several different
products is possible. (Scheme 1.2).
9
1 S
1-Np,- II P-S I I S-P
II '-R S
..
R is 1-Np or 2-Np
Scheme 1.2 The reaction of P .S,o and naphthalene.
2 has the steric protection given by the bromine atom that should prevent any reaction of
P .S,o at the 2 and 8 positions. Furthermore, the bromine atom has an inductive pull on
the electron density in the naphthalene thus deactivating it towards electrophilic aromatic
substitution. The resonance electron donation effect of the bromine atom is expected to be
smaller than the inductive effect.
Other routes to dithiadiphosphetane disulfides, using different starting materials are known
and they are shown below. All these routes are less convenient than aromatic
electrophilic substitution using P .S,o
1. The reaction of ten-butyl dichlorophosphine with lithium disulfide (equation 1.3).'0
2
Cl I P I '-Cl
Equation 1.3
This route requires a supply of the alkyl dichlorophosphine, which is more costly and less
convenient to handle than P .S,o. However, this route has been extended to give the
selenium heterocycle by the use of lithium diselenide.'o Similarly, a route to 2,4-diphenyl
1,3,2,4-diselenodiphosphetane 2,4-diselenide is the disproportionation of a reactive
selenium phosphorus intermediate formed by the treatment of PhPCI2 with Li2Se in THF."
The reaction of PsPhs with selenium (Scheme' 1.3) also provides access to P-Se
heterocycles. "
10
Se Ph __ p/ 'p __ Ph
\ I
1.2 Se
• P-P
/ \ Ph Ph
(PhP)s
13.3 Se
Ph I P
Se/' ...... Se \ I P-P
./ "'. Ph Ph
10 Se Se Se Ph \\ / '- / P P
/ '- / \\ Ph Se Se
Scheme 1.3 Reactions of PhsPs and selenium.
2. The reaction of hydrogen sulfide with dichlorophosphine sulfides (equation 1.4 and
Table 1.2).'2
Equation 1.4
Table 1.2 Reaction temperatures and yields for the formation of dithiadiphosphetane
disulfides from H2S and RP(S)CI2.'2
R Reaction Yield temperature ("C) (%)
Methyl 160-215 99
Ethyl 165-205 98
Propyl 170-205 80
iso-Propyl 170-205 92
Butyl 180-205 94
Phenyl 215-240 96
Cyclohexyl 200-215 86
This route has the disadvantages of high temperatures and the use of toxic H2S gas. In
addition the synthesis of the dichlorophosphine sulfides is required.
I I
3. The reaction of thiols with P .S,o (equation 1.5).'3
SH
4
R
6
CI-Q-CI
Cl
R is H orOMe
Equation 1.5
The above reaction has the disadvantage of requiring the use of the extremely offensive
smelling and toxic thiols, but the final products are reported to have greater solubility in
aprotic solvents than LR.'3
4. Exchange reaction.
While this reaction has not be used to form appreciable quantities of a product, it is
interesting as it demonstrates that solutions of dithiadiphosphetane disulfides contain
dithiophosphine ylides (Scheme 1.4)2
+ LR
(lip 43.2 ppm) (lip 14.8 ppm)
- Ss o-U/ 'P-An 's/II
S
(lipa 39.0 ppm and lipb 18.6 ppm)
Scheme 1.4 Exchange of phosphorus atoms between dithiadiphosphetane disulfides. .
12
The new dithiadiphosphetane disulfide was observed by 31p NMR spectroscopy' In
solution the dithiadiphosphetane disulfides are believed to be in equilibrium with a small
amount of the reactive dithiophosphine ylides. By increasing the steric bulk around the
phosphorus, the dithiophosphine ylides are made more stable (Scheme 1.5 and Table
1.3).14,15,16
Due to steric hindrance it would be unlikely that a stable dithiophosphine ylide could be
prepared by the reaction of an arene with P4S,0, Instead other routes to these compounds
are used. Either a primary phosphine is reacted with sulfur (or selenium)/base or a
phosphalkene/diphosphene is reacted with the a chalcogen. In some examples groups
with lone pairs are used to provide electronic stabilisation'4,15,16
t-Bu t-Bu t-Bu
t-Bu
a
S'::::'p'l'S
t-Bu
t-Bu
e
t-Bu
b
NMe2
Me t-Bu
S S NMe2'::::'P'l'
t-Bu
f
t-Bu
c
NMe2
t-Bu
OMe t-Bu
t-Bu
d
Se0- ""Se 0 ~p:;'--
N
t-Bu
9
Scheme 1.5 Stable meta-dithiophosphonates and a meta-diselenophosphonate.
Table 1.3 op values for the metadithiophosphonates and the metadiselenophosphonate.
Compound op(ppm)
a 298
b 285
c 278
d 171
e 150
f 145
g 148
13
Section 1.2 Results and discussion
The other routes to dithiadiphosphetane disulfides were rejected in favour of the shorter
and more simple route based on the reactions of P ,SlO' The best reaction temperature for
the formation of NpP,s. from P 4S,0 and 2 (Equation 1.6) was reinvestigated."
Br 2
S p/ "P
S'l' "S/ ~S
NpP2S4
Equation 1.6
It was found that the reaction of P 4SlO with 2 is very sensitive to small changes in the
conditions used. For example, carrying out the synthesis at 240°C gave insignificant
yields of NP2P2S" The mother liquor from the synthesis was found (by 3'P-{'H} NMR
spectroscopy) to be a complex mix1ure. After distillation a small trace of naphthalene (3)
was detected by GCMS (Ions found at 128 and 102 amu due to naphthalene and CBH;).
When the synthesis was attempted with chloronaphthalene rather than 2, an insignificant
yield of NpP2S. was obtained. The formation of the naphthalene can be rationalised as
being due to hydrogen abstraction from 2 by a 1-naphthyl radical (Equation 1.7).
Are
• H Equation 1.7
To allow the effects of an electron donating group para to one of the phosphorus atoms in
NpP2S4 to be investigated, a target molecule with a methoxy group at position 4 in NpP2S.
was selected. 1-Methoxynaphthalene (4) was selected as a suitable compound to react
with P 4S,0 to give the target molecule, because the methoxy group has a strong electron
donating effect into the aromatic ring by means of resonance effects, while it has a weak
inductive electron withdrawing effect. The resonance electron donation effect will activate
the 4 position strongly, so favouring the electrophilic substitution reaction at this site. The
methoxy group provides steric protection to the 2 and 8 positions. As expected 4 reacted
with P4S,0 to give, after cooling, a cream solid (Equation 1.8)."
OMe OMe
~ ~ P4S,O • Equation 1.8
:::::,... ~ 6
4 S p/ "P
S'l' "S/ ~S 14
MeONpP2S4
The 3'P-{'H} NMR spectrum of MeONpP,S. is of the AX type [17.5 and 16.9 ppm 2J (3'p_
31 p)=7.4 Hz] and in the 'H NMR spectrum five aromatic and one O-methyl environment
were found. These NMR results are in agreement with the structure of MeONpP,S •. Two
v(PS) vibrations due to the exocyclic sulfurs were seen at 698 and 658 cm" in the infra
red spectrum. For NpP,S. a single strong v(P=S) vibration is seen at 670 cm-', These IR
results are consistent with the weakening of the phosphorus sulfur bonds in one half of the
dithiadiphosphetane ring. The steric effects of the methoxy group are believed to be
negligible, but the methoxy group has electronic effects. The inductive pull on electron
density is much smaller than the resonance donation effect exerted on the phosphorus
para to the methoxy group (position 1). Those resonance forms in which one benzene ring
remains aromatic character are lower in energy and make a greater contribution to the
structure than the resonance forms in which the aromaticity on both benzene rings has
been disrupted.
The molecular structure of MeONpP,S. was determined (Figure 1.1 and Table 1.4) by X
Ray crystallography.17 No significant differences are observed in the P-S bond lengths of
NpP,S. and MeONpP,S. other than bond length P(S)-S(1S). This was shortest In
MeONpP,S. at 2.114(1) A compared to 2.122(1) A in NpP,S •. This difference is due to the
resonance electron donation effect of the methoxy group. In common with the other
molecular structures in this thesis the P=S bond length is shorter than the P-S bond
length, which is reasonable due to the difference in bond order. In common with NpP,S.
the rigid naphthalene portion of the molecule causes the dithiadiphosphetane ring to adopt
a cis folded shape in MeONpP,S •. The terminal sulfurs are pointing towards the centre of
the dithiadiphosphetane ring of another molecule of MeONpP,S •. The molecules of
MeONpP,S. have the naphthalene rings stacking face to face (3.51 A) with S(1) .... S(19)
intermolecular interactions (3.49 A).
Cll
S19'
Figure 1.1 Molecular structure of MeONpP,S •.
15
Table 1.4 Selected bond lengths (A) and angles (") in the molecular structures of NpP2S."
and MeONpP2S,.17
Bond NpP2S, MeONpP2S,
P(1 )-S(1) 1.913(2) 1.907(2)
P(9)-S(9) 1.912(2) 1.910(2)
P(1)-S(19) 2.126(2) 2.123(1)
P(9)-S(19) 2.122(1) 2.114(1)
P(1)-C(1) 1.805(6) 1.784(4)
P(9)-C(9) 1.809(6) 1.799(4)
S(19) ... S(19*) 3.05 3.06
P(1) .... .P(9) 3.25 3.24
mean P=S 1.913 1.909
mean P-S 2.124 2.119
1t-1t interplanar separation 3.56 3.51
S(1)-P(1)-S(19) 118.2(1) 117.8(1)
S(9)-P(9)-S( 19) 118.6(1) 118.6(1)
S(1)-P(1)-C(1) 117.5(2) 119.4(2)
S(9)-P(9)-C(9) 116.9(2) 117.6(2)
S(19)-P(1)-C(1) 103.7(1) 102.6(1 )
S( 19)-P(9)-C(9) 103.6(1 ) 102.6(1)
S( 19)-P( 1 )-S(19*) 91.6(1) 92.1(1)
S( 19)-P(9)-S(19*) 91.8(1) 92.6(1 )
P(1 )-S( 19)-P(9) 80.0(1 ) 80.2(1)
It was thought that 4 might react with P ,SlO at a lower temperature to form a stable
compound, such as a dithiadiphosphetane disulfide, which al a high temperature then
might react with more P,SlO to form MeONpP2S,. However when the reaction of P,S,o and
1-methoxynapthalene was repeated at a lower temperature no intermediates were
isolated - the only product obtained was MeONpP2S,.
In the reaction the first step is likely to be the attack of a phosphorus electrophile (Such as
P2SS) on the carbon para to the methoxy group. Once attached, the phosphorus sulfur
group could then act as an anchor to hold another phosphorus electrophile close to the 8
16
pOSition. It should be remembered that the 1,8 functionalisation of a naphthalene has to
overcome great steric difficulties, so this reaction has functionalized the naphthalene in an
uncommon way (Scheme 1.6).
OMe OMe
S=P / \
S S \ / P
S~ 'SH
Fast Step 1 OMe
-:?'
~ "'" .0
• Other phosphorus intermidates
Scheme 1.6 Partial mechanism for the formation of MeONpP2S •.
An attempt at making a related compound where the methoxy group had been replaced
with a butoxy group (Equation 1.9) gave no isolatable product but NMR (31 p-{'H} and 'H)
spectroscopy and MS (EI+) spectra were obtained from the crude product. It is believed
that 4-butoxynaptha-1 ,8-dienyl dithiadiphosphetane disulfide (5) was formed but due to its
extremely great solubility in petroleum ether and ether it could not be isolated. If 5 was a
liquid then it would be impossible to separate it from the excess arene by precipitation.
OBu OBu
Equation 1.9
4
It is known that the treatment of mesityl dichlorophosphine (6) with bis(trimethylsilyl)
sulfide (7) gives a puckered 1,3,5, 7,2,4,6,8-tetrathiatetraphosphocine (8) (p .S. ring)'·
17
This compound decomposes on mild heating to give dimesityl dithiadiphosphetane
disulfide (9) (Scheme 1.7)'8
6
Me3SiSSiMe3 (7) .
•
Ar \ P-S A
/ " /" r S P I
/p S Ar "S-P/ 8
\ Ar
Disproportionationl 35-400 C
S S Ar 11/ " r p p / "s/II
M S 9
Scheme 1.7 Formation of the tetrathiatetraphosphocane and its disproprotionation into a
dithiadiphosphetane disulfide.
Since ferrocenyl groups have a size midway between p-anisyl and tert-butyl (and mesityl)
they have been used to investigate the effect of altering the steric size of the carbon R
groups on the P2S2 ring. Furthermore, as ferrocenes are known to act as cytotoxins, '9,20
smoke suppressers:' antiknocking agents for petrol, redox active materials, and
conductive polymers,22 the synthesis of 2,4-diferrocenyl 1,3,2,4-dithiadiphosphetane 2,4-
disulfide (Fc,P,S.) was desirable. Finally, the introduction of ferrocenyl groups into a
molecule often allows the compound to be studied using electrochemical methods and
the question of Fe-Fe communication through a P2S2 ring seemed of interest.
Ferrocene (10) can be functionalised by metallation followed by reaction with an
electrophile. 23,24 However aromatic electrophilic substitution is an alternative method of
adding functionality (Scheme 1.8).23,25
18
o/Li ~ 2BuLi Fe .. Fe
BuLi "E+" ---;.~ FcLi ----'.~ FcE
~TMEDA Li 6
!"E+" !"E+" -H+ E+ is an electrophile
o/E
FcE
Fe
~E Scheme 1.8 8ubstitution of ferrocene with electrophiles.
As 10 is an electron rich aromatic compound its reaction with P 48'0 was considered, in the
expectation of a simple route to FC2P2S4' While the reaction of some phosphorus
electrophiles with 10 has been reported:6-2B it was unclear if the ferrocenyl groups would
survive treatment with P 4810'
~ 4 Fe
6 •
Xylenes d
ZQ Fe
~\ f5J 2 ~~=l \\
8 Fe "b FC2P2S4
Equation 1. 10
It was found that the reaction of lerrocene with P 4810 (in hot xylenes) gave FC2P28. in very
good yield (78%) and the synthesis may be scaled up to make larger amounts. The
mixture can be difficult to stir because much 01 the product separates out as a solid during
the reaction 2• The mother liquor was found (3'P-{'H} NMR) to be a complex mixture.
While the reaction of 10 with P48,o occurs at a higher temperature than the reactions of
19
phosphorus (Ill) electrophiles, the addition of a Lewis acid (AICI3) is not required. FC2P2S.
was found to be extremely insoluble in cold solvents, thus preventing solution state NMR
spectra and CV measurements. However it is reasonably soluble in hot toluene/xylene,
allowing recrystallisation and chemistry. Infra red spectrometry confirmed the presence of
the PS double bonds in the molecule [v(P=S) 670 cm-' ] and the detection of the
substituted ferrocene but it was impossible to be sure in what way the ferrocene was
substituted. Microanalysis confirmed the empirical formula of the compound. Mass
spectrometry detected no trace of the molecular ion (m/z 560) but the dithiophosphine
ylide or an isomer of it was detected at M/2 (m/z 280) amu.
The convenience and ease of formation of FC2P2S" suggested its use as a starting
material for other P-ferrocenyl phosphorus compounds. Treatment with chlorine gas gave
a black intractable mixture, while treatment with lithium triethylhydoborate gave a mixture
of products that included ferrocenyl phosphine.30 The experiment, if modified, might be the
basis for a shorter route to ferrocenyl phosphine. An existing route is the reduction of
ferrocenyl dichlorophosphine.3o
The structure of FC2P2S. (Figure 1.2 and Table 1.5) shows the ferrocenyl groups arranged
trans. The P2S2 ring is a distorted rectangular planar shape in contrast to the folded rings
that are seen in the structures for NpP2S." and MeONpP2S. H
Figure 1.2 Molecular structure of FC2P2S •. 29
20
Table 1.5 Selected bond lengths (A) and angles (0) from the molecular slructure of
Fc2P2S •.
P(1)-S(1) 2.134(3) P( 1 )-S( 1 )-P( 1*) 86.9(1)
P(1)-S(1*) 2.101(3) 5(1)-P(1)-5(1*) 93.1(1)
P(1)-5(2) 1.930(3) 5(1 )-P( 1 )-5(2) 115.2(1)
P(1)-C(1) 1.747(8) 5(1 )-P(1 )-C 107.8(3)
5(1) ... 5(1*) 2.91 5(1*)-P(1)-C 106.4(3)
P(1) ... P(1*) 3.08 5(1*)-P( 1 )-5(2) 115.9(1)
The structure has a centre of symmetry. The mean ring P-S distance of 2.118(4.2) A is not
significantly different to the P-5 distance reported in di-Iert-butyl dithiadiphosphetane
disulfide, while the P(1 )-P(1*) distance in di-Iert-butyl dithiadiphosphetane disulfide is
shorter, due to the difference in the shape of the P,5, rings in the two compounds. '°
It was postulated that by adding alkyl groups to the ferrocenyl group the solubility of the
product would be increased. To make a more soluble version of Fc2P,5., 1,1'
dimethylferrocene (11) was reacted with P.5 '0 to give 2,4-bis(dimethylferrocenyl) 1,3,2,4-
dithiadiphosphetane disulfide (12) lop 16.9 ppm, v(P=5) 680 cm"]' According to 'H NMR
spectroscopy this product is a mixture of isomers, because the substituted
cyclopentadienyl ring may have the methyl at the 2 or 3 position relative to the phosphorus
atom. 12 is more soluble in chloroform and xylenes than LR, NpP,5., MeONpP2S., or
Fc,P25 •.
The increase in solubility caused by the presence of the methyl groups allowed NMR
spectroscopy (op 16.9 pp m) and cyclic voltammetry measurements to be made in the
solution state. The cyclic voltammograms for 12 are shown below (Figure 1.3),32 Scan
rates of 20, 50, 100 and 200 mVs·l were used. For a reversible redox couple the potential
at which the peaks occur is independent of the scan rate.
0.' " Figure 1.3 Cyclic voltammogram for 12.
21
Compound 12 gave sharp peaks in the CV indicating that only one redox potential
(E' /,=0.52 V versus a SCE) occurs in the range 0 to 1.3 volt. (for 11 E'/, is 0.29 V).
31 p -{'H} NMR studies on a mix1ure of LR and 12 in COCI3 revealed, besides the peaks
due to starting materials, a pair of doublets that are assigned to 2-(para-methoxyphenyl)-
4-(dimethylferrocenyl) 1,3,2,4-dithiadiphosphetane 2,4-disulfide (13) with different groups
on the phosphorus atoms (Equation 1.11 and Table 1.6). This supports a report
suggesting the rapid dissociation of LR at room temperature.'
Me
~FeCPMe Equation 1.11 S S "/ ,
LR + 12 :;;,c==~h P P 13 AI 'S/ ''5
Table 1,6 Results from an exchange experiment using LR and 12.
Compound
LR
12
13
13
Op (ppm)
15.6
16.9
15.8
16.4
multiplicity
s
s
d
d
J (Hz)
7
7
As the methyl groups in 12 greatly increased its solubility compared with Fc,P,S., tert
butyl anisole was reacted with P.S '0 to create 2,4-bis(3-'butyl-4-methoxyphenyl) 1,3,2,4-
dithiadiphosphetane 2,4-disulfide (LR*) [op 17.2 ppm, v(P=S) 679 cm") a more soluble
version of LR. The 'butyl group prevent the molecules from packing tightly into a crystal
lattice, moreover the presence of the large group could provide steric protection for the
methoxy group. It has been suggested that the methoxy group in LR is involved in one of
the decomposition routes. (Scheme 1.9).
DMSO
OMe
~"L6 MeO
Nl S
O Ii s-p LSu
LSu J-~,©: S OMe
Mel/NaOH •
Scheme 1.9 Synthesis of LR*.
22
The 2-'butylanisole was made in good yield by the methylation of 2-'butylphenol in DMSO
using MeI/NaOH. 33.34 The use of LR' as a synthetic reagent will be described in a later
chapter. Again the presence of dithiophosphine ylides in solution can be demonstrated.
by 3'P-{'H} NMR spectroscopy.on a mixture of 12 and LR' (Equation 1.12 and Table 1.7).
LR* + 12 ;;;,r===.~
Me
~FeCPMe S S \\ / " P P ~ "S/\\ 9< 13a
MeO LSu Equation 1. 13
Table 1.7 Results from an exchange reaction using LR' and 12.
Compound
12
LR'
13a
13a
Op (ppm)
16.9
17.2
17.4
16.2
multiplicity
s
s
d
d
J (Hz)
7
7
The molecular structure has been obtained for LR' (Figure 1.4 and Table 1.8). confirming
the identity of LR' and revealing the lack of intermolecular interactions in the solid state.
The C-P bond lengths in LR' are longer than those found for FC2P25 •. while the P-S
(2.111 (2.8) A) and P=S (1.918(2) A) bonds are not significantly different in length to those
in Fc2P25 •.
Figure 1.4 Molecular structure of LR'.
23
Table 1.8 Selected bond lengths (A) and angles (0) from the molecular structure of LR*.
S(1)-P(1) 2.107(2) P(1)-S(1)-P(1) 87.21(7)
S(1)-P(1*) 2.114(2) S(1 )-P(1 )-S(1) 92.79(7)
S(2)-P(1 ) 1.918(2) S( 1 )-P( 1 )-S(2) 115.93(9)
P(1)-C(1) 1.793(5) S(1)-P(1)-C(1) 107.1(2)
S(1) .. (S1*) 2.91 S( 1*)-P( 1 )-S(2) 116.15(9)
P(1) .. (P1*) 3.06 S( 1*)-P( 1 )-C( 1) 106.5(2)
S(2)-P(1)-C(1) 115.7(2)
P(1 )-C(1 )-C(2) 120.0(4)
P( 1 )-C( 1 )-C(6) 119.8(4)
The structure of LR* has a centre of symmetry. In LR the molecules pack into layers with
the aromatic groups parallel with the sulfurs forming layers.31 It is likely that sulfur-sulfur
interactions help bind the molecules into the lattice.31 The non-bonded intramolecular S-S
and P-P distances are similar to those found in Fc2P2S" These distances are slightly
shorter than those in NpP2S. and MeONpP2S •. In the packing diagram (Figure 1.5) two
methyl groups of the telt-butyl group can be seen to intrude into the plane where the
endocyclic sulfur atoms are. One of the methyl groups of the telt-butyl group approaches
to within 3.6A of a exocyclic sulfur atom.3' The shortest intermolecular S-S distance is 3.9
A (Between endocyclic sulfurs of different molecules). This is similar to the shortest
intermolecular S-S distance in LR which is 4.0 A. In addition to altering the packing in the
crystal lattice the telt-butyl groups are likely to improve the solvation of LR* relative to LR
by making the non-polar lipophilic portion of the molecule larger.
Figure 1.5 Crystal packing diagram for LR*.
24
The reaction of 2-'bulyl-1-butoxybenzene with p.S,o gave (in a reasonable yield) 2,4-
bis(3-'bulyl-4-butoxyphenyl) 1,3,2,4-dithiadiphosphetane 2,4-disulfide (14) [Bp 18.4 ppm,
v(P=S) 679 cm-'I, 14 is less soluble than LR·. As the synthesis of 2-'bulyl-1-
butoxybenzene is more difficult than that of 2-'bulylanisole very little further work was
attempted with 14 (Scheme 1.10).
BuBr/NaOH • DMSO
OBu
~16 BUONl S o r-f'©(t.BU t.Bu p-s 0
I! S OBu
Scheme 1.10 Synthesis of 14.
25
Section 1.3 Experimental
Ether, THF, and petroleum ether were distilled from sodium/benzophenone before use.
Toluene was distilled from sodium metal. Anisole and xylenes were dried with sodium.
Anhydrous 1 ,2-dimethoxyethane (glyme) was used as received from Aldrich. All reactions
were carried out under an atmosphere of nitrogen gas in oven or flame dried glassware.
Lawesson's reagent (LR) was either obtained from Aldrich or was made by the reaction of
1 and P ,SlO. All ferrocenes, alkenes, dienes, cyanamides, alkyl lithiums and P ,S,o were
from Aldrich and were used as received. Imines other than N·benzylidene aniline were
prepared by the condensation of aldehydes with amines. Ortho·tert·butylanisole and other
alkoxyarenes were prepared by the alkylation of the phenol in DMSO and were distilled
from sodium before use. All NMR spectra, unless otherwise stated, were recorded using
solutions in CDCI3 in 5 mm tubes. 3'P-{'H}, 13C-{'H} and 'H NMR spectra were all
recorded using Jeol FX90a, and Bruker AX250 and DXP400 spectrometers. All 'H-{'H},
COSY, NOESY and 13C/'H correlations were recorded on the Bruker AX250. Methylene
carbons were identified by means of DEPT or Pendent experiments. Selected NMR
spectra were examined using geNMR software by Prof. J. Derek Woollins. Infrared
spectra were recorded with a Perkin Elmer IR system 2000, as KBr discs or thin liquid
films. Mass spectra were recorded using a Kratos MS80 and by the ERSPRC central
mass spectrometry service at Swansea. Microanalysis was carried out in the Chemistry
Department (Loughborough University) or at Astra Charnwood. Bu,NCIO, was from Fluka.
All cyclic voltammetry measurements unless otherwise stated were made using dilute
(circa 1 mmol dm-3) deoxygenated solutions in a 0.2 M solution of Bu,NCIO. in acetonitrile.
Square wave voltammetry experiments were performed using dilute (circa 1 mmol dm-3)
solutions in 0.1 M Bu,NCIO, in a mixture of acetonitrile and dichloromethane (1:1). All
electrochemical measurements were made using a saturated calomel electrode (SCE E'I,
of 0.2412 volt versus the standard hydrogen electrode) as the reference electrode;
ferrocene was used both as a reference and as a test compound before performing
experiments. All preparative chromatography, unless otherwise stated, was by means of
flash column chromatography. The stationary phase was silica. Prolonged exposure of
thiocarbonyls to light and oxygen was avoided when possible. All thiocarbonyl compounds
gave satisfactory spectroscopic data.
WARNING: Care should be exercised in the synthesis of the dithiadiphosphetane
disulfides as large volumes of hydrogen sulfide and other toxic fumes are produced,
these gases should be treated with sodium hypochlorite before release into an effective
fume cupboard. All mother liquors from these preparations contain high concentrations
of phosphorus sulfur compounds, these should be treated with sodium hypochlorite
solution taking due care to avoid any violent exotherms.
26
Naphthalene dithiadiphosphetane disulphide (NpP2S,)
1-Bromonaphthalene 2 (35 ml. 52 g. 250 mmol) was stirred with p.S" (10.8 g. 24 mmol),
in a 250 ml round bottomed flask fitted with a thermometer and a reflux condenser. The
flask was placed in a preheated oil bath (270°C). After the temperature in the flask had
reached 245°C, the flask was left in the bath for four minutes before it was removed. The
flask was allowed to cool to room temperature with magnetic stirring before the addition of
diethyl ether or toluene (40 ml). The solid was collected by filtration, washed with the
solvent and dried in vacuum to give NpP2S, as a cream/yellow solid (1.76 g. 5.57 mmol.
11%). IR 1597w, 1582w, 1555m, 1483m, 1436m, 1210w, 1145w, 1159m, 1071w, 992m,
901s, 826s, 759s, 741s, 670vs, 573s, 535s, 506s, 432s, 386m, 327m, 289m cm-'. op
(ppm) 15.5. OH (ppm); 8.9 (2H, m), 8.6 (2H, m) and 8.2 (2H, m). MS(EI+) mlz 316, 284,
252, 223, and 189. Expected isotropic distribution was observed for the molecular ion.
The mother liquor from the synthesis was subject to examination by 3'P-{'H} NMR, and
was found to be a complex mixture. 3'P_{'H} NMR o(ppm) (neat liquid with external C6D6
lock) singlets seen at 160, 103, 82.4, 67, 20 and -2. Many minor peaks seen between 90
and 10 ppm . Distillation of the mother liquor from two preparations gave a mixture of
bromonaphthalene and naphthalene (56g), and an evil smelling residue which was
examined by GCMS,
WARNING: The mother liquor from this synthesis can react particularly violently with
sodium hypochlorite. Some of these reactive compounds are sufficiently volatile to
codistill with ether/toluene.
4-methoxynaphthalene dithiadiphosphetane disulphide (MeONpP2S.).
1-Methoxynapthalene (10 ml. 10.9 g. 69 mmol) was stirred with p.S,o (2.92 g. 6.6 mmol),
in a 100 ml round bottomed flask fitted with a thermometer and a reflux condenser. The
flask was placed in a preheated oil bath (290°C). Four minutes after the temperature in the
flask had reached 245°C it was removed from the bath. After cooling to room temperature
with magnetic stirring, toluene (10 ml) was added. The mixture was stirred for several
hours before the product was collected by filtration and washed with toluene (10 ml) and
then twice with diethyl ether (10 ml and then 15 ml) before being dried in vacuum, to give
MeONpP2S. as a cream solid, (1.21 g. 3.5 mmol. 26%), which may be recrystallized from
toluene. The reaction has been scaled up (to 11 g P .S,o) successfully using a 250 ml
flask. A single crystal was obtained by cooling a hot toluene solution. (Found: C; 37,6; H;
2.0. C11 H.OP2S. requires C, 38.1; H, 2.3%). IR 3073w, 3004m, 2969m, 2926m, 2853w,
1601w, 1575m, 1561s, 1495m, 1456w, 1446m, 1407m, 1364w, 1350m, 1319w, 1263s,
27
1208m, 1186w, 1152m, 1104S, 1073w, 1014m, 946s, 885w, 827m, 801s, 759s, 741s,
698vs, 658vs, 597m, 547s, 513s, 483s, and 430s (cm·'). op (ppm); 17.5 (d), 16.9 (d)
2J [31 p.3'p)=7.4 Hz. OH (ppm); 8.8 (1 H, m), 8.6 [ddd, 4J ('H.'H)=1.3 Hz, 3 J(,H.'H)=7.3 Hz
and 3J(,'P.'H)=21 Hz), 8.5 [dd, 3J ('H.'H)=8.3 Hz and 3J (31 P.'H)=21 Hz) combined
integration for this peak and that at 8.6 (2H), 7.8 (1 H, m), 7.1 [1 H, dd, 4J(3'p-'H)=3.3 Hz
and 3J('H.'H)=8.3 Hz), 4.2 (3H, s). MS(EI) mlz 346 M+, 314, 251, 219, 204, 189, 176,
158,143,115, and 63.
Synthesis of FC2P2S4'
Ferrocene (5.2g. 28 mmol) was dissolved in xylenes (50 ml) P 4510 (3 g. 6.76 mmol) was
added and the mixture was boiled under reflux for 30 minutes. After cooling, FC2P2S4 was
collected as an orange solid by filtration. After washing with toluene the solid was dried in
vacuo to give the product (5.94 g. 10.6 mmol. 78%). For large scale preparations the
product can be washed with ether after the toluene washings before being dried in
vacuum. This preparation can be scaled up to 42 g ferrocene and 20.2g P 45'0' m.p.,
decomposes above 165°C to give a black solid not melting below 240°C. Found: C, 43.1;
H,2.97 (C20H,.Fe2P2S4 requires C, 42.9; H, 3.24%). IR 3093w, 3068w, 1407m, 1390m,
1364m, 1349m, 1310m, 1179s, 1169s, 1107m, 1023s, 1001m, 822s, 670s, 620m, 552s,
523s, 488s, 467s (cm·'). MS (EI+) m/z 280 (M/2\ 248 (FcPS), 217,184,147,121,56.
WARNING: Soon after the start of the reaction the rate of production of hydrogen
sulfide can become very high. Do not allow this gas production to become so rapid
that the foam of hydrogen sulfide and liquid could escape via the condenser. In the
event of the foaming becoming excessive reduce the heating of the reaction
mixture.
Reaction of FC2P2S4 to give ferrocenylphosphine.
FC2P2S4 (1.33 g) was suspended in THF (10 ml), LiEt3BH (19 ml of a 1 M solution in THF.
19 mmol) was added with care. A vigorous effervescence was seen and the FC2P2S4
dissolved to give an orange solution. A sample of this solution was placed in a NMR tube
(with CsDs). The fully proton decoupled 31 p NMR spectra were recorded first, then with
inverse gated 'H decoupling. Although the NMR indicated the presence of the desired
compound attempted distillation of the bulk of the reaction mixture did not give any
product.
Synthesis of 12
To 1,1'·Dimethylferrocene, 11, (0.92 g. 4.3 mmol) in xylenes (9 ml) was added P4S,o
(0.46 g. 1 mmol). The reaction mixture was heated under reflux for 2 minutes before the
28
addition of more xylene (9 ml), after 13 minutes more of heating the reaction mixture was
allowed to cool. The blood red solution was filtered to remove a small trace of a green
solid, hexane (5 ml) was used to wash the green solid and this washing was added to the
filtrate. More hexane (5 ml) was added and the filtrate was stored at -18 QC for 3 hours.
The solid orange product was collected by filtration and washed with hexane (10 ml) to
give bis(dimethylferrocenyl) dithiadiphosphetane disulfide (12) 0.279 g. 0.45 mmol. 11%.
(Found: C, 46.4; H, 3.8. C2,H26Fe2P2S, requires C, 46.8; 4.3, H). IR 3075w, 2947m,
2918m, 1475w, 1451w, 1382m, 1305w, 1251m, 1187w, 1097m, 1039m, 829m, 680s,
646m, 469s (cm''), op 16.9 ppm. OH (ppm) 4.8 to 4.0 (m), 2.0(m), and 1.9(m). MS(EI+) i11Iz
308 M/2+, 245, 198. CV, a reversible redox couple was observed at 0.52 volts versus a
SCE.
Synthesis of 2, 4-bis(3-tbutyl-4-methoxyphenyl) 1,3,2, 4-dithiadiphosphetane 2,4-disu/fide
(LR')
2-'Butylanisole (82.7 g. 504 mmol) and P ,S,. (26.9 g. 60.6 mmol) were heated in an oil
bath at 120-140QC until no yellow solid remained (ca. 90 minutes). At this stage there was
a brown heavy oil in the orange reaction mixture. The mixture was allowed to cool to room
temperature and stirred to cause a mass of yellow solid to crystallise. After the addition of
ether (100 ml) the solid mass was broken up and the solid collected by filtration, washed
with ether (100 ml), and dried in vacuum to give a yellow solid (37 g). This was dissolved
in boiling toluene (100 ml) and rapidly filtered while hot through a Celite pad into a large
Schlenk flask. After the solution was cooled slowly, the !!lother liquor was removed by
filtration and the resulting solid was dried in vacuo to give LR' (29.4 g. 57 mmol. 47%).
(Found: C, 51.4; H, 6.0; N, O.O;S, 24.6. C22H3.02P2S, requires C, 51.2; H, 5.8; N, 0.0; S,
24.8%). IR 3076w, 2997m, 2954s, 2937s, 2906s, 28665, 2838m, 1584s, 1560m, 1492s,
1483s, 1454s, 1437m, 1391m, 1383m, 1361m, 1308m, 1297m, 1254vs, 1200m, 1181m,
1146m, 1115vs, 1092m, 1020s, 928w, 896w, 878m, 8115, 721m, 679vs, 647s, 599m,
579m, 546m, 533w, 497w, 460vs, 409sh, 367w, and 326w (cm"). op (ppm) 18.2 s. oe
(ppm) 162.7, 139.0 (d, 15 Hz), 132.0 (d, 17 Hz), 131.4 (d, 17 Hz), 129.8 (d, 95 Hz), 111.2
(d, 19 Hz), 55.5, 35.6 , and 29.6. OH (ppm) 8.5 (1H, d, 19 Hz), 8.4 (1H, dd, 16.9 and 8.7
Hz), 7.1 (1H, dd, 'J[3'P-'Hl=5 Hz and 3J['H-'H)=8.6 Hz), 3.97 (3H, s) and 1.47 (9 H, s).
MS(EI) mlz 412,372,340,308,285,258 (M/2)+, 222, 195, and 158. Molecular ion found
at 258.0307 amu (12Cl1'H'5'603'p32S2 requires 258.0302 amu error of 1.8 ppm). MS(FAB)
mlz 765,741,735,719,539,523,516,501,493,483,471,297, 275, 267, 259, 257 and
many peaks below 250. MS(ES+) (mlz) 291 (MeOH2+[M/2)(, 259 ([M/2)H)+, and 111.
MS(ES-) mlz 290,289 (MeO+[M/2)r. and 157.
29
Synthesis of 2,4-bis(3-tbuty/-4-butoxypheny/) 1,3,2,4-dithiadiphosphetane 2,4-disu/fide
(14).
2-tert-butyl-l-butoxybenzene (6.65 g. 32 mmol) and p.S,o (1.77 g. 4 mmol) were heated in
an oil bath (120-160°C) for 40 minutes. After this time no P,S1Q remained, and the mixture
was allowed to cool. When the temperature was below 140°C a large amount of crystalline
solid formed. After cooling to room temperature the product was collected by filtration and
washed with 40-60 petroleum ether (4 ml). (Found: C, 59.8; H, 6.6; N, 0.0; S, 21.0
C2.H.20 2P2S. requires C, 56.0; H, 7.0; N, 0.0; S, 21.3%). IR 2998m, 1585m, 1560m,
1492m, 1483m, 1454m, 1437m, 1392w, 1383m, 1361m, 1308m, 1297m, 1254s, 1201m,
1181m, 1146m, 11145, 10935, 10205, 897w, 878m, 811s, 7225, 679vs, 6495, 599m,
578m, 546m, 532w, 497w, and 460 (cm-'). op (ppm) 18.4 (5), OH (ppm) 8.5 (0.42 H, m), 7.7
(1.37 H, m), 7.1 (0.21 H, m), 6.9 (0.74 H, m), 4.14 (t, 6 Hz) and 4.0 (m). Combined
integration height for the last two peaks is (2H), 1.9 to 0.9 multiplets (17 H). MS(EI) m/z
300,229,181 and 61.
30
Chapter 2
Metal Complexes from Diferrocenyl Dithiadiphosphetane Disulfide
Section 2.1 Introduction
Simple sulfur donor complexes can be obtained from a range of systems including
[Zn«S2P(O'Prhhl (15) (Equation 2.1) (16) which can also be used to give hetero-bimetallic
complexes such as (17) may be formed from the monothiophosphate (Equation 2.2)35
Zn[S2P(Oiprh12
15
Zn[OSP(Oipr)212
16
[PtCI2(PMe2Phhl •
iprO OiPr \ /
....... p ....... PhMe2P S 0 Cl
\ / \ / Pt Zn
/ \ / 'Cl PhMe2P S .............. O
P . / \ . IPrO O/Pr
17
Equation 2.2
Equation 2.1
In a related fashion LR reacts with group 10 metal bis-phosphine dichloride complexes
(Equation 2.3) and with [Pt(PPh3MC2H4)1 (Equation 2.4) with asymmetric cleavage of the
P S . 36 2 2 nng.
M is Ni, Pd, or Pt
AnP(S)CI2 +
PR3 may be a P,P,P-trialkyl, a P,P-dialkyl-P-aryl or a P-alkyl-P,P-diaryl phosphine
Equation 2.3
Equation 2.4
Furthermore, LR reacts with Grignard reagents to give anions (An)RPS, (18) (Equation
2.5 and Scheme 2.1), which have been used to form a variety of metal complexes.37,38,3.
S c+l S8 I±l 11
-MgX M X 2RMgX 1 g ---l.~ p __ ~ ".f---;l.~ ~P~S
An""l An/I R R
Equation 2.5
18
31
-----------
S S R' \\ / , / P P
R:-..;==;..-MgBr
/ 'S/ \\ R' S
R = Me3Si, Me and Et R' = Me and An
•
S 11 P
"~r R
1 Cr3+ 1 Zn
2+
Scheme 2,1 The reactions of dithiadiphosphetane disulfides with acetylene anions, to
form ligands for co-ordination chemistry.3.
A dithiophosphinic ester (19) can be formed by S-methylation of L with methyl iodide. The
alkyne portion of this molecule has been co-ordinated to a platinum (0) centre3• The C-C
alkyne stretching vibration is observed at 1700 cm-' (far below the expected frequency of
ca. 2200 cm-' for an alkyne), suggesting a reduction in the bond order of alkyne on
complexation 3• A related ligand (Ph,PS;) is known to co-ordinate to lead (11) ions to form
a polymeric material.·o LR was reacted with vinyl magnesium bromide followed by
ammonia to form 20, which after methylation gave 21, which upon treatment with KOH in
aqueous methanol to gave 22 (Scheme 2.2).38 22 reacts with cobalt sulphate to form a
cobalt complex_
S S U KOH/H20/MeOH U
An/' I 'OH .. An/' \'SMe
22 ~SMe 211/
1 Coso4_ 7H20
Co(C'OH'40 2PS2l2
Scheme 2_2 Formation of a chelate ligand from LR, and a cobalt complex.
32
Bis-Grignard reagents such as benzene-1,4-bis-magnesium bromide and 1,4-butane-1,4-
bis-(magnesium bromide) have been reacted with dithiadiphoshetane disulfides to give
Bis-(dithiophosphinic acids) (23) (Scheme 2.3) which have been used for the synthesis of
24 and 25 (Scheme 2.3).
S R G BrMgR'MgBr \I I / S ---l"~ P-R'-P
R = Me, Ph or An
THF Gs/ I \I R 2M9B\P S
[2312-
R' = 1,4-C6H4' 1,4-C4H., 1,6-C6H'2, 1,8-C.H'6 or 1,10-C,oH20
1. NH3 PCI5
S R \I ,I /SH P-R-P
2. Mel S R \\ I OH P-R'-P/
HS/ I \I R S
23
.. 3. KOH H20/MeOH
HO/ I \\ R S
25
Scheme 2.3 Formation, and further reactions, of bis-dithiophosphinic acids from
dithiadiphosphetane disulfides.
The reaction of LR with triiron dodecacarbonyl has been reported to give 26, a complex
where all the phosphorus sulfur single bonds have been broken (Equation 2.6). The
phosphorus and sulfur atoms cap the upper and lower faces of the three iron triangle each
ligand is a 4 electron donor and the iron atoms have 18 valence electrons.
LR Li2S ..
j CP'Ti"/CO
/ 'CO Cp
S Cp S __ ..i. ..... An ,/ .. li I
cp/ 'S--P,--S An
28
[Fe3(CO}g(~3-S)(~3-P(S)An)l
26
SLi S~ I/SLi
"" P/ I An
Scheme 2.4 Formation of titanium complexes from LR.
Equation 2.6
33
Titanium complexes (27) and (28) were obtained as shown in Scheme 2.4.42 These
compounds might be of some use in the synthesis of sulfur phosphorus rings, as the
sulfur titanium bond is a weak bond which could be broken in favour of a stronger bond
(e.g. with elimination ofCp,TiCI,).
LR behaves as a thionation reagent towards 29 removing one oxygen atom and replacing
it with sulfur forming 30 (Equation 2.7).43
LR
(BU4Nt4 [PW,,Nb04014- .. MeCN/AcOH
29
(BU4Nt4 [PW11Nb039S14-60% 30
Equation 2.7
Clearly LR exhibits some interesting reactivity towards metal centres. It was of interest to
establish if FC2P,S4 behaved in a similar fashion. Apart from the reaction chemistry the
presence of a ferrocenyl group in a ligand enables the use of cyclic voltammetry to
investigate the electronic effect of the metal on the ligand. For example 4'-ferrocenyl
2,2':6',2"-terpyridine (31) L (E'I, 0.53 volt) shows an increase in redox potential when co
ordinated to ruthenium (11) (E'l, for [Ru(L),][PF61, is 0.54 volt) (Scheme 2.5).44
Fc [Ru(Lh][PFs12
31 (L)
Scheme 2.5 4'-ferrocenyl 2,2':6',2"-terpyridine (31) and its complex with ruthenium.
For 32, 33, 34, and 35 the E'12 values suggest that on complexation to the Re (I) centre
the ligands become slightly more electron poor," while when one hydrogen on ferrocene
is substituted for [Re(CO)51 (in 34), the ferrocene becomes more electron rich (Scheme
2.6 and Table 2.1).45 Complex 36, like 32,33,34 and 35, is formally a Re (I) complex
(assuming the ferrocenyl groupto be an anionic ligand) or it could be argued that it is a Re
(0) complex. The redox potential of 36 is lower than that of ferrocene suggesting that the
rhenium portion of the molecule is donating electrons into the ferrocenyl group while for
the other rhenium complexes the metal centre is withdrawing electron density from the
34
lerrocenyl groups. Spectroelectrochemistry (IR) suggests lor 32, 33, 34, 35 and 36 that
while no great change to the overall structure 01 the complexes occurs when the lerrocene
group is oxidised, the oxidised ligands are less electron donating.45
32
Ph I Cl
Fe-P, I ...... CO / Re
Ph OC" I 'CO CO
33
'O,© " " I ...... CO Re o CO P
1'CO
35 Fe
Cl FePh2P, I ...... CO
Re FePh2P" I 'CO
CO
34
CO Fe, I ...... CO
Re OC,. I 'CO
CO
36
Scheme 2,6 Complexes 01 rhenium with ligands containing lerrocenyl groups.
Table 2.1 Electrochemical data lor rhenium complexes and the Iigands45
Compound E'/2 E't, 01 ligand (volts)" (volts)"
32 0.63 0.49b
33 0.39 0.36
34 0.38,0.48' 0.36
35 0.33" 0.32
36 -0.03 0.22c
• All measurements made in CH2CI,t0.1 M [Bu.N)[CIO.l relative to a AglAgCI electrode,
redox potentials then were converted to be relative to a SCE. b Irreversible redox couple,
value quoted is the peak oxidising current. c E'/2 ollerrocene. 'Two redox couples seen .•
Measurement made in MeCN/0.1 M [Bu.N)[CIO.J.
35
Section 2.2 Results and Discussion
The reaction of Fe,P,S. with bis-phosphine platinum dichloride complexes was attempted.
It was anticipated that the reaction would give a bimetallic system. While platinum can be
redox active it was expected that the ferrocenyl group would not be affected greatly by the
presence of this element in the complex. However the ferrocenyl group does allow the
electrochemical investigation of the complex by cyclic voltammetry.
Fe,P,S. was found to react readily with bis-phosphine platinum dichlorides in THF to give
chelate complexes of the FcPS3 dianion (Equation 2.8 and Table 2.2). This is similar to the
reaction of LR with bis-phosphine platinum dichlorides. The two chlorine atoms are
believed to be incorporated into a molecule of P-ferrocenyl dichlorophosphine sulfide. a
literature precedent does exist3•
Equation 2.8
Table 2.2 Platinum complexes containing the ligand FcP(S)S2'
Compound PR3
37 PEt3
38 PMe3
39 dppe
40 PBu3
For 37 two phosphorus chemical environments with platinum satellites were observed
[," po• 3.3 ppm (3108 Hz) and 31 Po, 92.0 ppm (215 Hz)]. The first environment 0. is due to
the two phosphine ligands while 0, is due to the new ligand. The 31 p-{'HJ NMR shifts are
similar to those obtained for related compounds. 36
The molecular structure for 37 was obtained (Figure 2.1 and Table 2.3). In this molecular
structure the platinum is in a distorted square planar arrangement. The intra-ring P-S bond
lengths are shorter than the corresponding distances in Fe,P,S •. suggesting that the P-S
bonding in 37 is stronger. The mean P-S length of 2.059 A is shorter than the P-S bond
lengths for organo phosphorus sulfur compounds 41- 46 (Scheme 2.7).
36
S(1)
Figure 2.1 Molecular structure of compound 37.
Table 2.3 Selected bond lengths (A) and angles (0) found in the molecular structure of 37.
Pt-S(1) 2.367(3) S( 1 )-Pt-S(2) 81.6(1)
Pt-S(2) 2.360(3) S(1)-Pt-P(3) 90.8(1)
Pt-P(2) 2.227(3) S(1 )-Pt-P(3) 167.2(1)
Pt-P(3) 2.267(4) S(2)-Pt-P(2) 86.2(1 )
S( 1 )-P( 1 ) 2.049(5) S(2)-Pt-P(3) 172.4(1)
S(2)-P(1 ) 2.068(4) P(2)-Pt-P(3) 101.4(1)
S(3)-P(1 ) 1.934(5) Pt-S(1 )-P(1) 89.8(1)
C(1)-P(1) 1.78(1) Pt-S(2)-P(1 ) 89.5(1 )
S(1)-P(1)-S(2) 97.2(2)
P(1) ... Pt 3.13 A S(1)-P(1)-S(3) 118.2(2)
S(1 ) ... S(2) 3.09A S(1)-P(1)-C(1) 107.3(5)
S(2)-P(1 )-S(3) 114.7(2)
S(2)-P(1)-C(1) 108.0(5)
S(3)-P(1)-C(1) 110.4(5)
P(2)-Pt-P(3) 101.4(1)
37
x:~\ S
s
pi s
X-S cb:sll ~S," II
It !'Fe !'Fe P-Fe
/'S/"-.Ph I yS Fe Fe
R
41 42 43 44 R=Ph 45, RdBu 46
Scheme 2.7 Phosphorus sulfur compounds.
The P(2)-Pt-P(3) angle [101.4(1)"j is enlarged and this can be rationalised as being due
to the steric repulsion between the two phosphine ligands. The platinum centre has a
distorted square planar geometry with the Pt atom lying 0,05 A from the mean plane of its
substituents. The PtS2P ring is shaped like a butterfly with the PtS2 and PS2 planes being
inclined by 15° to each other, P(1) lies 0.35 A out of the plane of S(1),Pt and S(2).
Similarly shaped PtS2P rings have been observed in the molecular structures of [Ti(115-
MeCp),(S2(S)PAn)] (29),42 [Pt(S2(S)PAn)(PPh3),] (18)36 and [Pt(S2P(OEt)'h(PPh3ll (47)46
(Scheme 2.8) where the angle between planes MS2 and PS2 are 12.9°, 19.4° and 10.2°.
MeCp S ',/S " / , " 1i P M C / 's/ \ e p An
29
EtO S EtO~p/:
1 : S : S OEt 'pr '\:o-p/
Ph3P/ 's/ 'OEt
47
Scheme 2.8 Titanium and platinum complexes,
The Pt-S distances are not significantly different from those found for the ch elating
[S2P(OEt)'f ligand in [Pt(S2P(OEt),),(PPh3)] (47) and within the range observed for 18.
No attempt was made to investigate compounds 39, 40, 41' and 42 as reagents for
converting carbonyl compounds into thiocarbonyls since the soft chemical nature of
platinum (11) would make the exchange of the sulfur atoms in the chelate rings unlikely. In
addition the high price of platinum would make any stoichiometric thionation reagent
containing it extremely expensive. Encouraged by the reaction of FC2P2S, with platinum
bis phosphine dichlorides, the reaction of platinum bis(triethylphosphine) dichloride with 48
and 49 was attempted (Scheme 2,9).
s 11
/P,NHPh Fc NHPh
49
Scheme 2.9 Nitrogen phosphorus sulfur compounds 48 and 49.
38
2,4-0iferrocenyl-3-phenyl 1,3,2,4-thiazadiphosphetane disulfide (48) was found not to
react with platinum bis(triethylphosphine) dichloride (Equation 2.9). The two compounds
were dissolved in COCI, and the resulting solution, even after being allowed to stand for a
prolonged time, showed no new products by 31 p-{'H} NMR spectroscopy. The reason for
this lack of reaction could be that the phosphorus nitrogen bond is stronger than the
phosphorus sulfur bond.
Pt(Et3P)zCI2
X ~ Equation 2.9
FcP(S)(NHPh), (49) and platinum bis(triethylphosphine) dichloride were dissolved in
COCI, and to this solution was added a trace of triethyl amine (Equation 2.10). This
mixture hours showed no new products by 31 p-{'H} NMR spectroscopy after 4 hours.
S 11
/P,NHPh Fc NHPh
49
Pt(Et3P)zCI2
X~ Equation 2.10
Et3N
39
Section 2.3 Experimental
Synthesis of 37.
FC2P2S, (18.9 mg. 34 mmol) and [PtCI2(PEt3h] (17.0 mg. 34 mmol) were stirred together
in deoxygenated THF (deoxygenated by at least 3 freeze/pump/thaw cycles) (1 ml). Within
minutes the FC2P2S, started to react to give an orange solution. After stirring overnight,
hexane (5 ml) (deoxygenated) was added. The resulting yellow solid was allowed to settle,
before the removal of the supernatant liquid. After washing with more hexane the solid (23
mg. 30.9 mmol. 91%) was dried in vacuo. Crystals of 37 suitable for X-ray studies were
obtained by the vapour diffusion of dichloromethane into a toluene solution.
IR 3094w, 3079w, 2961s, 2930m, 2875m, 1451m, 1412m, 1380w, 1370w, 1349w, 1312w,
1255w, 1237w, 1187w, 1164m, 1106m, 1034s, 1015s, 1002w, 892w, 883w, 858w, 834w,
822s, 806w, 771m, 754s, 745s, 726m, 709m, 666vs, 634m, 571w, 559w, 542m, 507w,
493s, 445m, 424m, 424m, 402w, 382m, 339m, 312w, 296w, and 287w (cm-'). op (ppm)
3.3 'J{Pt-P} 3108 Hz and 92.0 3J{pt_p} 215 Hz. OH (ppm), 4.73 m, 4.31 s, 4.30 m, 1.91 m,
and 1.16 m. MS(FAB) miz 767 (M+Nat, 744 (M+Ht, 743(M+), 728(M-16t ;Expected
isotropic distribution found for (M+Nat ion.
N.B. Signals for 37 with a proton or sodium ion associated were observed in the results of
the FAB MS experiment.
Synthesis of 38 .
The reaction of [PtCI2(PMe3h] (22 mg. 52.6 flmol) and FC2P2S, (30 mg. 53.6 flmol) in THF
(1 ml) was carried out using ultrasound for 5 min followed by stirring overnight to give a
yellow slurry. To this was added deoxygenated petrol. [Pt(S2P(S)Fc)(PMe3h] was
obtained in quantitative yield.
(Found: C, 31.8; H, 3.9. C'6H27FeP,PtS3 requires C, 29.1; H, 4.1%). IR 3090w, 2969s,
2909m, 2853w, 1414m, 1383w, 1309w, 1289m, 1181w, 1289m, 1105w, 1062m, 1018m,
999w, 965s, 946s, 858m, 821m, 743m, 661s, 625w, 583m, 541m, 493s, 435w, 391m,
369m, and 340m (cm-'). op (ppm) 3.2 ['J(31 p-Pt)=3100 Hz] and 91.9m. MS(FAB) m/z
659(M+), 644(M-16)+, 490, 413,391 and 345.
Synthesis of 39
The reaction of [PtCI2dppe] (23 mg. 34.6 flmol) and FC2P2S. (19 mg. 33.9 flmol) was
carried out in THF (3 ml) as above, using ultrasound for 5 minutes before stirring
overnight. The THF was removed in vacuo before the addition of hexane, to give
[Pt(S2P(S)Fc)(dppe)] as a yellow solid (29 mg. 32.0 flmol. 94%).
(Found: C, 47.2; H, 3.6. C'6H33FeP3PtS3 requires C, 47.7; H, 3.7). IR 3074w, 3050m,
2956s, 2925s, 2867w, 1483m, 1435s, 1409m, 1166m, 1105s, 1018m, 998m, 879w, 822
40
------
br, 748 br, 716s, 706s, 692vs, 665vs, 534vs, 486s, 378w, and 343w (cm·'). op (ppm)
97.72 [2J(31 p_PI)=229 Hzl, 42.05 ['J(31 p-PI)=3132 Hzl. OH (ppm), 7.7 (br), 7.5 (br), 4.7 (m),
4.3 (m), and 4.2 (s). MS(FAB) mlz 1026, 928, 906(M+), and 890(M-16(.
Synthesis of 40
The reaclion of [PICI2(Bu3Phl (15 mg. 22.4 flmol) and FC2P2S, (13 mg. 23.2 flmol) in THF
gave an orange solulion. To Ihis was added hexane (2 ml) 10 give [PI(S2P(S)Fc)(PBu3hl
as yellow solid, after washing wilh hexane and drying (15 mg. 16.5 flMol. 74%).
(Found: C, 44.3; H, 6.4; N, 0.2. C34H63FeP3PIS3 requires C, 44.8; H, 7.0; N, 0.0). IR
3099m, 2956s, 2927s, 2867m, 1462m, 1407m, 1379w, 1209w, 1167m, 1093m, 1050w,
1017m, 967w, 904m, 815m, 799m, 773w, 720m, 666 vs, 542m, 490m, 463w, 402w, 377w,
341w, 310w (cm·'). op (ppm) 90.7 [2J("P-PI)=206 Hzl, and 4.4 ['J(31 p-PI)=3103 Hz]. OH
(ppm), 4.7 (m), 4.36 (s), 4.3 (m), 1.8 (br), 1.4 (br), and 0.95 (I, 7.0 Hz). MS(FAB) m/z
1026, 928, 906(M+), and 890([M-16f). CV, reversible redox couple al 0.54 voll versus a
SCE.
41
Chapter 3
Thionation of Organic Compounds
Section 3.1 Introduction
A range of reagents exists for the conversion of carbonyl compounds to thiocarbonyls in a
single step. These include H,S/HCI46.47• 6,S348 (EtO),P(S)SH49 and p.S'046 all of which
have major disadvantages. H,S is a toxic offensive-smelling gas, 8,S3' unless made in
situ, is of low efficiency.48 (EtO),P(S)SH is acidic and P4S,o varies in effectiveness
between batches and is very insoluble.46
Some multistep methods for the synthesis of thiocarbonyls exist e.g., via Vilsmeier salts,so
and by the reactions of Grignard reagents with CS" followed by an activating agent and
an amines" or by reacting N,N-dimethylthiocarbamoyl chloride with Grignard reagents in
the presence of a nickel (11) catalystS' (Scheme 3.1).
O.
R' 11 '""N/"'-.... R
I R'
Tf20, (COCI),. CO(OCC~),. or Cl
POCI3 R' e J --•• -......:~R
I R' cf'
-Me3SiCI
S
R' 11
'"" N/"'-.... R I R"
t,.Tf20 12. NHR'R"
S CS, 11
RMgX • /"'-.... XMgS R
Scheme 3.1 Multistep routes to thioamides.
• RMgX NiCI2dppe
Other routes to thiocarbonyl compounds, such as the reaction of cyanamides with
hydrogen sulfides3 (Equation 3.1) and amines with isothiocyanates (Equation 3.2) are also
known.
Np S
>-< Me NH2
Equation 3. 1
R'R"NH RNCS Equation 3.2
R" may be H
42
Selenocarbonyls are accessible via several routes, such as by the reaction of amides with
either phosphorus" (Equation 3.3) or boron" (Equation 3.4) based reagents.
Ar Se I Se \I __ P ____ I!
Ar/P
'S 11 s(p 'Ar e n
Equation 3.3
Se Ar = 2,4-bis (tert-butyl)-6-methoxyphenyl
Equation 3.4 B-Se-B--
Chloropurines have been converted to selenopurines conveniently with sodium hydrogen
selenide (Equation 3.5)56
Cl Se
NaSeH Oc' H, :Jc' > .. N > H2O
HO XAN N HO XAN N Equation 3.5 0 0
OH OH X can be H or NH2
OH OH
Another route to selenocarbonyls is by reacting an acetylene anion with selenium,
followed by either an amine and an allyl halide or a thiol (Scheme 3.2)57
Ph--===---H
Ph
BuLi/Se ..
.. 0 Sigmatropic r
c=se
f I C,-,<_~""m'", Ph Se
Ph--===----SeLi
l~Br Ph-..;;;;=--,--Se
i9~
RSH SeLi
Ph I ~SR
..
1~Br Se
Ph SR
Scheme 3.2 Route to selenocarbonyls from acetylenes, amines and allyl halides. 43
Lawesson's reagent (Scheme 3.3) has been widely used for the thionation of carbonyl
compounds to the corresponding thiocarbonyls in a single step, '6.58 such as the
conversion of N-Z dipeptide and N-Boc dipeptide esters to the endo thiodipeptide diesters
with retention of the configuration at the chiral centres.59 Furthermore, a phosphine oxide
has been converted into a phosphine sulfide (50) by Lawesson's reagent (Scheme 3.3).60
o 11
CI-P-CI 1 Adm
S 11
CI-P-CI 1 Adm
50
Scheme 3.3 Thionation of both carbonyls and a phosphine oxide by Lawesson's reagent.
However it should noted that Lawesson's reagent can cause epimerization of a
stereocentre e.g., in the attempted thionation of two bicyclic lactam esters 51a and 51b
that gave 52a and 52a (Scheme 3.4)61
~4~u ""'~
51 H R
LR
E= COOEt
Isomerization •
Scheme 3.4 Lawesson's reagent induced epimerization.
44
Commercial LR converts a sensitive amide (53) to a nitrile (54), while after
recrystallization LR gives reasonable yield of the thioamide (55) (Scheme 3.5).62
Prolonged heating of the reaction mixture results in conversion of 55 to the 54. It is
thought that the phosphorus side products from the thionation can convert 55 to 5462.63
The rapid formation of 54 when using commercial LR, is believed to be due to impurities in
the LR. 62 In this work the use of FC2P2S, and MeONpP2S. gave slightly lower yields of the
thioamide, while far less of the nitrile was formed (Table 3.1 ).62.63 LR* gave a similar yield
to LR with almost none of the nitrile being formed (Table 3.1)62.63
o
/ 53 S
CN
00 •
54
Scheme 3.5 LR acting as either a dehydration or thionation reagent.
Table 3.1 Formation of 54 and 55 from 53 using different thionation reagents62.63
Thionation agent Length of reflux Yield of 55(%) Yield of 54(%) in benzene (h)
MeONpP2S. 24 26 <5 FC2P2S. 24 37 <5 LR* 3 58 trace LR 24 0 80 LR (best results ever) 64 30
A recent paper describes a direct route from alcohols to thiols using LR.64 This reaction
also gives alkenes and heterocycles with some alcohols (Scheme 3.6). It unlikely that this
reaction could be used for forming thiols from phenols because of competing reactions
(See chapter 4)65
R~ LR R~SH •
Scheme 3.6 Formation of either thiols or alkenes from alcohols by LR.
As a side reaction of the thiol synthesis, alkenes may be formed64. By the treatment of
alkyl phosphates and alkyl thiophosphates with Lawesson's reagent alkenes are obtained
in high yield (Scheme 3.7).66
45
RO R
P(O)(OMe), P(S)(OMe),
LR
LR •
Yield of alkenes
79% 69%
Yield of alkene
P(O)(OMeh 100% P(S)(OMeh 75%
ct:·ct
Scheme 3.7 Conversion of trialkyl phosphates to alkenes.
LR can reduce a range of sulfoxides to sulfides and disulfides2.67
,68 This reduction can be
used to reduce cephalosporin sulfoxides to the sulfide (Equation 3.6)68 With
nitrosobenezenes LR gives
obtained (Equation 3.7)69
08
BnCONHU~(£l
~ N o
o 0
Ar-NO
azobenzenes, and in one case an azoxybenzene was
LR
Equation 3.6
80%
LR Equation 3.7
46
With N-Nitroso amines, Lawesson's reagent forms 1,3,2-thiaazaphosphetanes (56) and
4,5-benzo-1,3,2-thiazaphospholes (57),70 while with N-Nitrosoamides isothiocyanates,
thioamides and a dihydro-2(3H)-thiophenone have been obtained (Scheme 3.8).70
R is H or Pr
R is H or Pr
S II
&$% lCc~
RT· I "'" Ny ;-::; S
LR
1300 C RT1Yo NO
QS+ N I H 80%
~O 6%
62%
Scheme 3.8 N-Nitroso compounds reacting with LR. 70
Nitrones and the pyridine-N-oxides were deoxygenated with the formation of elemental
sulfur as a co-product.66 On treatment with Lawesson's reagent quinoline-N-oxide was
found to form mainly quinoline and elemental sulfur with a small amount of quinoline-2-
thione as well. The quinoline-2-thione is believed to have formed by means of a
rearrangement of the qUinoline-N-sulphide intermediate.66
The combination of Lawesson's reagent and silver perchlorate acts as a very effective
catalytic system both for the Diels Alder reactions of a,p-unsaturated ketones (Equation
3.8),71 and for the formation of P-D-Ribofuranosides from D-Ribofuranose and alcohols
(Scheme 3.9 and Table 3.2)n
AgCI04 and Lawesson's reagent
CH2C12 /-780 C 16 hours H Equation 3.871
CHO
47
Bnotpp AgCIO. and Lawesson's reagent OH •
a + ROH Benzene I RT I 2 hours
o 0 Bn........ ......Bn
ROH=~OH (y0H
V HO Cholesterol
OH
Bno~ or BnO o en' OMe
Scheme 3,9 LRJAgCIO. acting as a Lewis acid catalyst.72
Table 3,2 LRJAgCIO. acting as a Lewis acid catalyst.72
Alcohol Yield (%) alp ratio 3-phenylpropan-1-o1 97 5:95
Cyclohexanol 93 5:95
Cholesterol 90 4:96
Methyl a-2,3,4-tri-O-benzyl-D-glycoside 79 24:76
By reacting Lawesson's reagent with lithium sulphide, lithium P-anisyl trithiophosphate
(59) is formed. 59 does not thionate benzophenone, so the reaction of Lawesson's
reagent is probably not driven by nucleophilic attack on the carbonyl group (Equation
3.9). ,
S
LR.. An-U-SLi I SLi
59
Equation 3.9
Neither [TiCp,{AnPS3-S,S11 (29) (Figure 3.1) or [Ni{AnPS3-S,S1{dppe}] were found to
thionate benzophenone.' This suggests that the monomeric RPS, intermediates are
required for the thionation reaction.2
Cp S S , / , ~ 1i P
cl '8/ 'An 29
Figure 3,1 Compound 29.
48
1,2-0xazole (60) was converted to 1,2,4-thiadiazole (61). This reaction is believed to
occur through replacement of the oxygen with sulphur followed by rearrangement
(Scheme 3.10)'»
H R
'N-\ PhJj 0
60
R= Me or Ph
Scheme 3.10 Thionation followed by rearrangement.
Treatment of Lawesson's reagent with phenylhydrazones of acyclic ketones gave 2,4-
dihydro-1,2,3-diazaphospholes, in most cases as the sole product in high yield. This
reaction is believed to be a nucleophilic attack on the Lawesson's reagent followed by the
elimination of hydrogen sulphide to form the ring,74 The reaction of the phenylhydrazones
(62) of cyclohexanone and cyclopentanone gave both the gave 2,4-dihydro-1,2,3-
diazaphospholes (63) as well as indoles (64) formed by a Fischer indole synthesis,
catalysed by the Lawesson's reagent (Scheme 3.11 ),74
¥ N
N/ "H
R~ 62
R'
R'
.. R
64
R'
Ry-\S //
+ P N / 'An ---N
I Ph
63
Scheme 3.11 Formation of both indoles and gave 2,4-dihydro-1,2,3-diazaphospholes.
1,4,5,6,7,7a-Hexahydro-2H-indol-2-ones (65) with LR do not give the expected
thioamides, but instead furnished the 4,5,6,7-tetrahydroindoles (66).75 This reaction was
also attempted with 1,5-dihydropyrrole-2-ones (67). These on treatment with Lawesson's
reagent gave the thioamides (68) with pyrroles (69) as minor products (Scheme 3.12).75
49
(X)=o LR CD • \
66 \ 65 Ar Ar
~o LR ~S 0 .. + N
I I I Ar Ar Ar
67 68 69
Scheme 3.12 Synthesis of pyrroles.
Lawesson's reagent forms an imidazoline ring (70) from a l3-amino amide, the
stereochemistry at the carbon a to the amide carbonyl carbon being unaffected (Equation
3.10).76
OMe OMe
MeO MeO
Equation 3.10 LR ..
By reacting a-diazoketones with Lawesson's reagent 1,2,3-thiadiazoles can be prepared.
This reaction works welf for a-diazoketones where the ketone and the diazo group are
held cis, for instance in 2-diazo-1-acenapthenone (71) which gives (72).'1 The reaction is
likely to be via a diazothioketone that then forms the 1,2,3-thiadiazole ring (Scheme 3.13) n,7B
1.1 equiv LR .. .. 2 equiv HMPA 7"' 4. CeHe
71 72 48% Scheme 3.13 Synthesis of a 1,2,3-thiadiazole.
This reaction also has been carried out for 10-diazo-9-phenanthrone (73) and a-diazo 13-ketoesters (74) to give 1 ,2,3-thiadiazoles as products (Scheme 3.14)n.78
50
o
73
o 0
R2y'OR1
N2 74
1.1 Eqiv LR
•
LR
N S/ ':::-N
R2~OR1 o
R1 can be allyl, Me, Bn, tert-butyl and CH2CH2SiMe3
R2 can be Me, Et, cyclopentyl and tert-Butyl
Scheme 3.14 Synthesis of other 1,2,3-thiadiazoles.
When the size of R' is increased the reaction forming the thiadiazole requires more
forcing conditions.7• Changing R2 causes much less change.7• No thiadiazole (75)
formation was observed for azibenzil (76), which would be reasonable as the molecule is
not likely to be in the cis arrangement (Equation 3.11)n
o Ph LR
H Ph N2
76
Equation 3.11
By reacting 1,4-diketones (77) with LR, thiophenes (78) can be formed (Equation 3.12 and
Table 3.3).79.'0 The reaction gives better yields and occurs under milder conditions than
the synthesis using P .SlO. 79 The reaction is thought to go via a 1,4 dithioketone that then
undergoes the ring closing reaction79. This reaction is very useful for the synthesis of
symmetric 1,4-disubstituted thiophenes as effective synthesis routes for symmetric 1,4-
disubstituted 1,4-diketones do exist.a,
R~R' o 0
77
LR R--O--R'
S Equation 3.12
78
51
Table 3.3 Yields of thiophenes from diketones.79,80
R R' Yield (%)
Me Me 87
Ph Me 80
p-Tolyl Me 86
An Me 90
p-BrCsH4 Me 98
Ph Ph 80
p-Tolyl p-Tolyl 70
Ph An 62
This reaction can tolerate semi-cyclic trisubstituted 1,4-diketones such as 79 and 80 to
give thiophenes fused to other rings 81 and 82. This can be used as part of the synthesis
of benzothiophenes (83) if an oxidation step is then used (Scheme 3.15)82
LR
OO-Ph [0]
©r)-Ph .. .. 81 91% 83 91%
LR CO-Ph .. 82 58%
Scheme 3.15 Synthesis of 2,3-benzo[bjthiophenes and 2-phenylcyclopentathiophene.
The reaction can be performed with 1,4-dithienyl-1,4-butane-dione (84),80 Furans (85) can
be formed instead from the more substituted diketones (Equation 3.13 and Table 3.4)83
This could be due to the steric effects of the phenyl groups, the presence of electron
donating groups on the aromatic groups [J. to the carbonyls increases the yield of furans
while electron withdrawing groups in these locations lowers the yield of the furan 83 The
presence of two electron withdrawing groups (nitro groups) in the diketone [l,4-diphenyl-
2,3-bis-(4-nitrophenyl)-butane-1 ,4-dionej84 favours the thiophene synthesis over the furan
formation when compared with the reaction of 1,2,3,4-tetraphenyl-butane-1,4-dione with
LR83
R' R" R' R" R' R" RXR,,_LR_ .. RnR'" + RnR'" o 0 0 S
85
Equation 3.13
52
Table 3.4 Yields of heterocycles formed by the treatment of diketones with 1.2 equivalents
ofLR.
R R' R" R'" Yield (%) Reference Furan Thiophene
Ph H H Ph 0 80 83 Ph H Me Ph 11 89 83 Ph H Ph Ph 28 72 83 Ph H An Ph 47 53 83 Ph Ph Ph Ph 89 11 83 p-Tolyl Ph Ph p-Tolyl 91 9 83 An Ph Ph An 90 10 83 Ph P-N02C6H, P-N02C6H, Ph 83 84
LR was used in the attempted synthesis of [10](2,5)thiopheneophane (86). Instead of
forming this it acted as a dehydrating agent in a Paal-Knorr synthesis of
[1 0](2,5)furoanophene (87). P ,5'0 gave a small yield of 86 (Scheme 3.16)85
86 87
Scheme 3.16 [1 0](2,5)thiopheneophane and [10](2,5)furoanophene.
A related thiophene synthesis is the reaction of p,y-epoxycarbonyls with LR in the
presence of tosic acid (Scheme 3.17 and Table 3.5)86
• • yS@ OH
R R"
LR
R'
1l
--Ys
• R R" -H20
R'
--1kOH •
R- 1 -R"
R'
VSH@
OH
R R"
R'
Scheme 3.17 Formation of thiophenes from p,y-epoxyketones86
53
Table 3.5 Overall yields of thiophenes from l3,y-epoxyketones.86
R R' R" Yield (%)
Sec-Bu CH,CI H 64
Cy CH,CI H 63
1-Adm CH,CI H 57
CH,CH,COOMe CH,CI H 42
p-FC6H. CH,CI H 56
2-Thienyl CH,CI H 52
Sec-Bu H Me 72
CH,CH,COOMe H Me 63
Ph H Me 83
1-Thienyl H Me 70
The ring forming chemistry has been extended to the synthesis of 5-aminothiazoles (88)
from diamides (89), and this synthesis step can be used as part of a ready synthesis of
fused bicyclic products from more simple starting materials (Scheme 3.18)87
o An 11 0 C1
Nil,
LR •
-HCI
Scheme 3.18 SyntheSiS of 5-aminothiazoles.
69
88
By the reaction of 3-aryl-2,1-benzisoxazoles (90) with Lawesson's reagent
dibenzo[b,f][1,5]-diazocines (91) can be formed in good yield in a simple synthesis
(Equation 3.14 and Table 3.6)88
Ar
Ri R2 \ LR Equation 3. 14 0 ~
R R2 N- Ri
90 Ar
Ar 91
54
Table 3.6 Yields of dibenzo[b,f][1 ,5j-diazocines"
R, R, Ar Yield(%)
Cl H Ph 82 Br H Ph 78 Cl H An 79 NO, H Ph 67 Cl Me Ph 74
55
Section 3.2 Results and discussion
Lawesson's reagent (LR) is employed for thionation of carbonyl compounds,·6.s. often at
elevated temperatures due to the low solubility of LR. Here the transformation of 4,4'
dimethyoxybenzophenone (92) to 4,4'-dimethoxybenzothione (93) was used to
investigate a selection of phosphorus sulfur compounds (Scheme 3.19 and Table 3.7) as
thionation reagents. The phosphorus sulfur compounds were heated with 92 in bOiling
toluene. Only LR, FC2P25., and NpP,s. gave yields of thione (93) above 80%. With all
other compounds (other than 96) 93 was obtained in poor yield. For the
dithiadiphosphetane disulfides (LR, LR*, NpP25., and FC2P2S.) the test reaction was
repeated with benzophenone (97). In the case of 48 the ketone for the thionation test was
xanthone (98)
S S S
co'::::'P(s:::p-r
::?' I "" ~ ..?'
NpP25•
48
OMe MeONpP 2S.
S
/~---II IV-J-l---Fe
43
S 11 PPh,
Ph,PS
94
41
MeO
s 11 P
Fe"'-- \'NMez NCS
95
S Fe \\ I
P 0/ '0
Fe ___ ~ ~_Fe II '0/ \\
Ss I11 'P P, I11 Ss
LR*
S S
96
OMe
Scheme 3.19 Phosphorus sulfur compounds tested for activity as thionation reagents.
56
Table 3.7 Results of the screening of possible thionation reagents.
Phosphorus compound Ketone Length of reaction Yield
(h) (%)
LR 92 1 100'
LR 97 1 78
NpP2S. 92 1 94
NpP2S. 97 1 17
MeONpP2S. 92 1 6
FC2P2S, 92 1 87"
FC2P2S, 97 1 66
LR* 92 1 98
LR* 97 1 100
Ph,PS 92 15.5 0"
dppaS2 92 16 0"
41 92 1 44b
43 92 16 trace"
48 98 15 98c.d
94 92 15.5 10
95 92 1.5 9
96 92 5 37b,0
" No (or very) little change found by TLC. b Yield estimated by 'H NMR spectroscopy. C
Yield measured by GCMS. d Yield based on the assumption that three atoms of sulfur per
molecule of phosphorus compound are transferred to the substrate in exchange for
oxygen atoms .• Product was recrystallized from ethanol.
Clearly many of the sulfur phosphorus compounds are ineffective as thionation reagents,
so they were subject to no further testing. The dithiadiphosphetane disulfides with the
naphthalene backbone were much less reactive than LR as the two phosphorus atoms
are held close together in space. In view of these results, the thionation reactions LR*
which contains solubilising alkyl groups were examined.
57
LR* was found to thionate 4,4'-dimethoxybenzophenone (92) to thioketone (93). A test of
how effective LR* was when compared with LR and FC2P2S. was needed. The relative
thionating ability of LR, LR*, and FC2P2S. were tested with a variety of compounds
(Scheme 3.20 and Table 3.8). By using conditions under which LR gives a moderate yield
any differences between the effectiveness of the different thionation reagents would be
more likely to be clear. By reducing the temperature, time of reaction or polarity of solvent
the yields obtained with LR were often reduced greatly from those stated in the literature.
Then using identical conditions (and work-up) the reaction was repeated with LR*
(sometimes also with FC2P2S,). All thionated compounds gave satisfactory spectral data.
o
)l An 92 An
o H
)--~ Ph 99 Ph
S H
)--N~ Ph 100 Ph
o SOS
6666 101 102
PhVPh
104 E
RAO
0 S
Ph)lOBu PhAOBU 113 114
116
107 108
Ph-flr-Ph
o 0 103
R E
Ph 0 Ph S Me 0 Me S
Scheme 3.20 Substrates and thionated products.
109 110 111 112
58
Table 3.8 Reactions of LR, LR·, and FC2P2S, at elevated temperatures with carbonyl
compounds and an alcohol.
Substrate Product Solvent Yield with thionation reagent (%)
LR FC2P2S.LR·
92 9389 Petrol 9 1 27
99 10090 PetrollToluene 14 trace 39
101 10291 Toluene 100 66 a
10392 10479 Toluene 99 90 90
105 10693 Glyme 43 0 65
107 10894 Toluene 60 b 6c
109 110 Glyme 48 0 34
111 11295 Glyme 35 b 11
113 114 Toluene 23 b 41
115 11696 Toluene 70 76 76
a. Could not isolated pure by flash column chromatography.
b. Reaction not attempted
c. Not isolated pure, yield estimated by 1 H NMR spectroscopy or GCMS.
In most cases LR· was either more or equally effective as a thionation reagent than LR or
FC2P2S.. However for the caprolactone and caprolactam the product was grossly
contaminated with phosphorus side products. These could not be removed by flash
column chromatography.
Cholesterol esters were found to react more slowly with LR· than with LR. This is likely to
be due to a steric effect. The formation of thioesters using LR can require high
temperatures and long reaction times, so the low yields obtained in the synthesis of 110
and 112 are reasonable. Only limited NMR data had been published for 112 while for 110
no NMR data were available. The thiocarbonyl Qc values for 108, 110, 112 and 114 were
similar to those reported for thioesters (Table 3.9)97
59
Table 3.9 Oc NMR values for thioester thiocarbonyl carbons·7
Compound OC(C=S) (ppm)
108 227.5
110 219.0
112 210.4
114 211.7
C.H'3C(S)OEt 224.6
'-BuC(S)OBn 224.1
PhC(S)OMe 212.2
PhC(S)OEt 211.4
PhC(S)O'Pr 210.9
PhC(S)OBn 211.2
1-NpC(S)OEt 215.6
2-NpC(S)OEt 211.1
When N,N'-diphenyl urea (117) was reacted with Fc,P,S., a complex mixture of products
was obtained from which only 49 could be isolated, and as thioureas can be obtained with
ease by the reactions of isothiocyanates and thiocarbamoyl chlorides with amines the
reactions of ureas with phosphorus sulfur thionation reagents was not investigated further.
It was found that when an excess of 92 was treated with LR or LR* for 18 hours in
refluxing toluene, more than two moles of 93 were formed per mole of thionation reagent.
This does suggest that 3 or 4 sulfur atoms per molecule can be used in thionation
reactions, rather than only 2 as would be initially expected and as is reported to be the
case. This fact also suggests that the oxygen containing side products from LRlLR* are
able to act as thionation reagents.
As LR* is more soluble than LR, the use of LR* as a thionation reagent for use at room
temperature was investigated (Table 3.10). Carbonyl compounds were stirred in either
toluene or CH,CI, with either LR or LR*, before the product was isolated by means of
chromatography. Xanthone (98) (Scheme 3.21) was used in these room temperature
experiments.
o
98
S
o 118
Scheme 3.21 Xanthone and Xanthione. 60
Table 3.10 Room temperature thionation reactions.
Substrate Thionation Solvent Time Product Yield
reagent
92 LR Toluene 140 min NA 0
92 LR* Toluene 140 min 93 36
92 LR CH2CI2 15 h 93 84
92 LR* CH2CI2 15 h 93 86
103 LR Toluene 65 h 104 77"
103 LR* Toluene 43 h 104 77"
98 LR Toluene 16 h 11898 28"
98 LR CH2CI2 22 h 118 75
98 LR* Toluene 15 h 118 100
98 LR* CH2CI2 160 min 118 100
109 LR* Toluene 8 days NA OC
105 LR* d 7 weeks NA OC
113 LR* d 7 weeks NA OC
a. 4% of the furan was present in the thiophene product by GCMS
b. Not isolated pure, yield estimated with 'H NMR or GCMS.
c. Very little or no product detected by TLC
d. Stirred in CH2CI2 for 7 days before the addition of toluene (10 ml).
It was found that at room temperature, LR* was either more or equally effective as a
thionation reagent when compared with LR. Esters and lactones would not react at room
temperature with LR*. It was found that LR as a suspension in CH2CI2 is more effective as
a thionation reagent than when in toluene. This could be due to the increased polarity of
the solvent. It is noteworthy that a thiophene can be formed at room temperature from a
l,4-diketone. These conditions are very mild compared to those often used.
In conclusion, LR* has been shown in most of the examples to be an effective thionation
reagent both at room temperature and above. It is likely that LR* can be used as
thionation reagent under mild conditions.
61
Section 3.3 Experimental
Reactions of test compounds with thionation reagents.
Typically compounds were heated in a solvent with the thionation reagent before being
allowed to cool. Flash column chromatography on Si02 was used to obtain the product as
a pure compound.
LR (0.63 g. 1.55 mmol) and 92 (0.63 g. 3.11 mmol) were heated in petroleum ether (100
ml) for 30 minutes, chromatography (CH2C1:,Jpetroleum ether 4:6) gave 93 (69 mg. 270
",mol. 9%) as a deep blue solid.
99 (0.615g. 3.12 mmol) and LR (0.65g. 1.61 mmol) were heated in petroleum ether (80
ml) mixed with toluene (20 ml) for 90 minutes. Chromatography (CH2CI2/petroleum ether
4:6) gave 100 (95 mg. 446 ",mol. 14 %) as a yellow solid.
101 (119 mg. 1.05 mmol) and FC2P2S4 (300 mg. 5.36 ",mol) were heated in toluene (10
ml) for 55 minutes. Chromatography (CH2CI2) gave 102 (89 mg. 690 ",mol. 66%) as a
white solid.
103 (81 mg. 340 mmol) and LR· (198 mg. 354 mmol) were heated in toluene (6 ml) for 45
minutes. Chromatography (petroleum ether) gave 104 (72 mg. 305 ",mol. 90%) as an off
white solid.
105 (149 mg. 1.11 mmol) and LR (240 mg. 0.59 mmol) were heated in glyme (2.5 ml) for 2
hours. After removal of solvent, chromatography (CH2CI,Ipetroleum ether 1:9) gave 106
(72 mg. 480 ",mol. 43%) as a yellow solid.
107 (0.4 ml. 0.41 g. 3.6 mmol) and LR (0.78 g. 1.9 mmol) were heated in toluene (10 ml)
for 30 minutes. Chromatography (11 9 Si02. 60 ml petroleum ether followed by 25% ether
in petroleum ether) gave 108 (0.28 g. 2.16 mmol. 60%) as a yellow oil.
109 (288 mg. 588 mmol) and LR (550 mg. 1.36 mmol) in glyme (4 ml) were heated (17
hours) before the addition of LR (250 mg. 0.62 mmol) after a further heating (24 hours) the
solvent was removed, chromatography (petroleum ether) gave 110 (142 mg. 587 mmol.
48%) as a yellow solids.
111 (266 mg. 620 m'!1ol) and LR (593 mg. 1.47 mmol) were heated in glyme (4 ml) for 48
hours. After removal of solvent, the residue was extracted with petroleum ether (7 ml)
62
followed by CH,CI, (2.5 ml) and these extracts applied to a flash column. Chromatography
(petroleum ether) gave 112 (96 mg. 216 mmol. 35%) as a white solid.
115 (198 mg. 1.0 mmol) and Fc,P,S. (276 mg. 493 J.lmol) in toluene (10 ml) were heated
(70 min). By TLC 115 was absent. After filtration through SiO, chromatography (3 9 SiO"
petroleum ether) gave 1, 1-diphenylethene (116) as a yellow oil (138 mg. 766 J.lmol. 76%).
By GCMS this was a single compound.
Typical room temperature reactions.
106 (75 mg) and LR* (179 mg) were stirred in toluene (10 ml). Chromatography
(petroleum ether) gave 107 with a trace of the furan present.
105 (141 mg) and LR* (0.31 g) were stirred in CH,CI, (7 ml) for 7 days before the addition
of toluene (10 ml). Even after 7 weeks very little change could be observed by TLC.
117 (0.5 ml) and LR* (0.74 g) were stirred in CH,CI, (10 ml) for 7 days before the addition
of toluene (10 ml) (To replace the CH,CI, that was evaporating). Even after 7 weeks very
little change could be observed by TLC.
Xanthone (98) (199 mg. 1.01 mmol) and LR (248 mg. 0.614 mmol) were stirred in toluene
(10 ml), chromatography (without concentration) (CH,CI,/petroleum ether 4:6) gave
98/118 as a mixture.
98 (191 mg. 0.97 mmol) and LR (223 mg. 0.55 mmol) were stirred in CH,CI, for 22 hours
before removal of solvent. Chromatography (CH,CI,tpetroleum ether 3:7) gave 118 (88
mg. 0.41 mmol. 75%) as a dark green solid.
Treatment of LR and LR* with excess 92 under forcing conditions.
LR (270 mg. 0.67 mmol) and 92 (663 mg. 2.7 mmol) were heated in toluene (11 ml) (18
hours), chromatography (CH,CI,/petroleum ether 4:6) gave 93 as a blue/black solid (566
mg. 2.19 mmol. 82%).
LR* (333 mg. 0.65 mmol) and 92 (670 mg. 2.77 mmol) were heated in toluene (10 ml) for
18 hours, chromatography gave 93 (645 mg. 2.50 mmol. 96%).
63
Synthesis of 113 from 114.
To LR (0.571 g. 1.41 mmol) was added 113 (0.5 ml. 0.505 g. 2.81 mmol) and to this was
added toluene (10 ml). This mixture was then refluxed for 30 minutes. After cooling and
removal of solvent, chromatography on silica (elution with petroleum ether) gave, after
removal of solvent, 114 as a yellow oil (42 mg. 216 mmol. 8%). IR (thin film) 3067m,
29595, 28725, 1596m, 14515, 1380m, 13165, 12725, 12355, 11765, 1156w, 1099m,
10765,10525,10255, 927m, 843w, 7725, 732w, 6885, 637m (cm-1). OH (ppm) 8.20 (2H, d,
8 Hz), 7.5 (1H, t, 7 Hz), 7.4 (2H, t, 8 Hz), 4.7 (2H, t, 6.5 Hz), 1.9 (2H, m), 1.6 (2H, m), 1.0
(3H, t, 7 Hz). On irradiation of the peak at 4.7 ppm the multiplet at 1.9 became a triplet (8
Hz). Oc (ppm), 211.7 (quat), 138.6 (quat), 132.6, 128.7, 128.1, 72.6 (CH2), 30.4 (CH2),
19.5 (CH2), and 13.8. MS(EI) m/z 194 (M+), 161, 139, 121, 105, 77, 56, 51,41 and 29.
Molecular mass measured by HRMS at 194.0765 amu ('2CI1'H14'·032S requires 194.0765
amu, within 0.1 ppm). Due to the likely offensive smell and toxic nature of 114 no
microanalysis was attempted.
64
Chapter 4 Reactions of Dithiadiphosphetane Disulphide with
Catechols
Section 4.1 Introduction
Dithiadiphosphetane disulfides undergo ring cleavage on treatment with nucleophiles and after
subsequent electrophilic alkylation give compounds which may be useful as insecticides
(Equation 4.1). 100,101,102.
R Me or p-MeOCsH4 R' Me, Et or LPr M Na or K X CN, F, NCS or N3 Y Br or I
1. MX 2. R'Y
EtOAc
S 11 P
W/ \'SR' + MY X Equation 4. 1
The oxygen phosphorus bonds are normally expected to be stronger than the sulfur
phosphorus bonds found in dithiadiphosphetane disulfides. LR is known to (eact with water,
phenols and alcohols to give compounds in which the phosphorus atoms are more electron
deficient, due to the greater electronegativity of oxygen relative to sulfur (Table 4.1).'03 The
steric effects of any carbon groups attached to the oxygen atoms are believed to protect the
phosphorus centre from attack by nucleophiles.
Table 4.1 Electronegativity values (Alfred-Rochow).,a3
Element
Oxygen
Sulfur
Electronegativity
3.50
2.44
In a commercially important reaction p.S ,a is reacted with simple alcohols (ethanol and
methanol) as a step in the synthesis of parathion (119) (Equation 4.2).
ROH P4S'0 ~ Equation 4.2
R can be Me or Et
Likewise the reaction of dithiadiphosphetane disulfides with alcohols can be used as a step in
the synthesis of insecticides" In many insecticides that are acetylcholinesterase inhibitors, the
65
phosphorus atom bears two lipophilic groups which gives more scope for 'fine tuning' of the
properties of the final product.
Current concerns about toxicity are likely to reduce the interest in new phosphorus
insecticides; however past research on their synthesis by the reaction of oxygen nucleophiles
with dithiadiphosphetane disulfides has given a large amount of information about this
reaction. LR and other dithiadiphosphetane disulfides react with primary alcohols such as
ethanol. The initial products 120 and 121 can be converted readily into 122, 123 and 124
(Scheme 4.1 )6.65
S 11 P-SH
An/' 'OEt 1400 C
121 1 Xylene 1400 C
S 11
/,P-SEt + An 'OEt
123
S S 11 11 P P
An/' 1 'S ....... I 'An OEt OEt
124
Scheme 4.1 Reactions of primary alcohols with LR65
S 11
/,P-SEt An 'OEt
123
Heating causes two molecules of the phosphonodithioate to couple together, with the loss of
hydrogen sulfide, to give compound 124. This reaction takes place by means of attack of the
thiol
S II ....... SR P
An/' , OR
123
S 11 P-SH
An/' 'OR
1 Xylene 1400 C
S S + 11 NHAr + 11 ~NHAr
/,P"" /,P"" An 'OR An 'NHAr
127 128
121
R'X S 11
----;.~ P-SR' An/' 'OR
123
Scheme 4.2 Treatment of 121 with para-toluidine (126)65
66
group on a phosphorus centre, whereas 123 is formed via attack of the thiol group of 121, as
a nucleophile on the alkoxy group on another molecule of 121.65 Reactions of 121 with carbon
containing electrophiles are illustrated in Scheme 4.2.65 The formation of 127 and 128 can all
be explained by the nucleophilic attack of the amine on the phosphorus atoms.
Reaction of secondary alcohols and LR in hot xylene with either pyridine or amine 126
present, gives a variety of different products including 128- 13465, as well as the salt 135.65
The increase in steric bulk about the oxygen atom is likely to be responsible for the differences
in the chemistry from the above example (Schemes 4.3 and 4.4).
rrlsCHMePh
An-P \ SCHMePh
131
S SiBu rr rr I11 + P P
An-p\ . An/" I 'S/" I 'An OlBu OlBu O'Bu
129
PhMeCHOH .. Xylene/Pyridine
1400C
r i-BuOH 130
Xylene/Pyridine 1400C
PhMeCHOH LR • +
Xylene/toludine 1400 C
1 i-BuOH
Xylene/toludine 1400C
+
rr/NHAr
An-P \ NHAr
12
rrlCHMePh
An-P 13 \ SCHMePh
rrlCHMePh
An-P 132 \ NHAr
S SiBu rr/NHAr An-~I + An-P Ar = pC6H.Me
\ . \ O'Bu NHAr
129 128 Scheme 4.3 Treatment of LR with secondary alcohols. 65
S 11 P
S S S <±> 11 p-MeC6H.NH
An/" I 'SCy OCy
133
11 11 + P P
An/" I 'S/" I '-An OCy OCy
134
Xylene/Pyridine
6.
Xylene/toludine
6.
Scheme 4.4 Treatment of LR with cyclohexanol. 65
P e An/" I 's
OCy
135
The reaction of tertiary alcohols with LR gives, as the sole product, An3P30 3S3 (136) (op 72
ppm)65.104 (Scheme 4.5).65
67
OH
1 ~. [ ~_~:0yH 1
it. OH 1 ~ 750
C
Scheme 4.5 Reaction of LR with tert-butanol. 65
When tert-butanol is reacted with LR in the presence of 126. it was reported that the sole
product was 128.65 Thiols have been shown to give similar products to those obtained with
ethanol6' Phenol reacts with LR (at 140°C) to form 137 (Scheme 4.6).6'
~ ~ ... __ [ An-tll-SH j ... _P_hO_H_ An/I 'S/ 1 'An 1400 C
OPh OPh OPh
137
S 11
An-P-SR 1
RSH/· SR
/~ylene LR 1400 C
""-RSH
C6H~ 800 C
S S 11 11 P P
R can be Ph, Bn, CH(Me)ph, or 2-Np An/I 'S/ 1 'An SR SR
Scheme 4.6 Reactions of phenol and thiols with LR6•
Oximes have been found to react with LR, to form a variety of compounds (Schemes 4.7 and
4.8), the outcome of the reaction being dependent on the structure of the oxime.'o, In most of
the reactions the oxophilic phosphorus atom becomes bonded to the oxygen either in the
formation of a heterocycle or in the thionation of oxime to a thiocarbonyl (which may
oligomerise).'os However, in hot benzene a complex mixture of products including an
azaphosphorine is formed (Scheme 4.7).'05
68
N Ar--( 'p
S-P-An 11 S
p-Tol S p-Tol i Ar~:1 Y Y p-ToICH=NOH RR'C=NOH S S .. LR ~ ~ CsHs
~TOI 250
C
CSHsl NOH aooc )l
Ph Me
An S \ II
H,-~/P"lI
Ph~Ph
S SH R ~p/
)= / "-N-O Ar
R'
S~ SMe R "p/
)= / "-N-O Ar
R'
Ar can be Ph, artha, meta and para-MeC6H.. R,R' can be Me,Me; Me,Ph; CH2CH2CH2CH2CH2; CH2CH2CH2CH2; and Ph,Sn.
Scheme 4.7 Reactions of oximes with LR. 105
Ph
F NOH
R
Rt. S Proton ~NPh 11 transfer S ~ ~.. \
R NHPh O-P=S
H'J ,l.r
R can be Phenyl, or 2-thienyl.
Scheme 4.8 Reaction ofaximes of diaryl ketones with LR to form thioamides. ,o5
Oxygen nucleophiles containing two sites for reaction such as ethylene glycol can react with a
dithiadiphosphetane disulfide using one or two sites. The reactions of 1 ,2-diols 106 and
catechols 107 with LR have been recently investigated. These reactions were found to give
heterocycles 138,'07 139,'06 and 140. '06 Mechanistically these reactions can be rationalised
69
as being due to an SH group acting as a leaving group (Scheme 4.9), hydrogen sulfide gas
will be formed by these reactions.
2~OH ~OH S 0JQJ
2 ''pi 0 -2H2S
•
• An/ , o
S 0
"I J An/P
, o 139
+
138
S S 11 S 11
An-P/ 'P-An I \ o 0 "--/
140 Scheme 4.9 Reactions of catechol and ethylene glycol with LR.
Recently some dioxaphospholane phospholipid (141) analogues have been reported to exhibit
selective herbicidal activity against rape (Equation 4.3)'08
OR
• \:
0 S 'p-:I'
I " o An
Equation 4.3 LR
141
Before this work there have been few studies of the reactions of NpP,S4 with oxygen
nucleophiles. The reaction of methanol to give 142 {op 79.8 (d), and 66.4 [d, 2J (31 p _31 p)=15
Hz]) cannot be explained by the simple action of methanol as a nucleophile, as one methyl
group is transferred from an oxygen on to a sulfur atom (Equation 4.4).'09 142 could be related
to an intermediate in the conversion of alcohols to thiols by LR. 64
MeOH •
OMe SMe S",I IhS '-'p p:/"
'S/
Equation 4.4
The reaction of ethylene glycol with NpP,S4 to give 143 (op 78.6 ppm) can be explained by the
nucleophilic attack of two molecules of the diol on the phosphorus centres, followed by
70
elimination of hydrogen sulfide (Equation 4.5)."0 The fact both the hydroxyl groups of one
molecule of the diol do not react to give a C202P2S ring is difficult to explain.
/\ Equation 4.5
HO OH
•
143
Further treatment with ethylene glycol at 140°C gives 144 (Bp 6.6 ppm), which would be the
logical hydrolysis product (Equation 4.6). Surprisingly, attempts to form 144 by the action of
water on 143 have failed"o
Equation 4.6
1400 C
143 144
71
Section 4.2 Results and discussion
In this work the reaction of NpP2S, with 3,S-di-'-butylcatechol (145) was found to give 146. The
formation of 146 can be explained via a stepwise reaction path. One of the hydroxyl groups
reacts with the phosphorus electrophile then intramolecular attack of the second hydroxyl
group is rapid to give an intermediate that can eliminate H,S to give 146 (Scheme 4.11). The
3'p-{'H} NMR spectrum of 146 is an AX type (IiA 74.4 ppm lix 71.2 ppm). The 'J coupling
constant is 3.S Hz 17.111 which is half of the 7.0 Hz 'J coupling constant found for MeONpP2S.
17 while the corresponding coupling constant for 142 is greater. ,OO•11' The lip values are
intermediate between those observed for dithiadiphosphetane disulfides and
dioxophospholanes (Scheme 4.12 and Table 4.2)'07 The mean lip value for 146 (72.8 ppm) is
lower than that found
555
CO~P::::5:::;P""
,y ""
"" I "" •
HO
5 55 (""5 ~~ ~~
66p
P~:? 145
,y I "" H _____ •
~ A Then proton transfer
•
146 Scheme 4.11 Reaction of NpP2S. and 145 to form 146.
1 Then proton transfer
for a 1,3,6,2,7-thiadioxodiphosphepane (89.9 ppm) (Scheme 4.12)'07 but is within 6 ppm of
the value for 143 (78.6 ppm)."0
S S 11 S 11
An-P""- -""'P-An I \ o 0 "-/
140
Scheme 4.12 8enzo-1 ,3,2-dioxaphospholanes and a 1,3,6,2, 7-thiadioxodiphosphepane. 72
Table 4.2 3' P NMR spectroscopy data for benzo-1 ,3,2-dioxaphospholanes. '07
R 0.( pp m)
H 108.8 '-Bu 109.4 Ph3C 109.8
The 'H NMR spectrum of 146 is complicated by the overlap of several multiplets but is
consistent with the structure of the product. However, because the two aromatic ring systems
are separated by a POS portion of the molecule it is almost impossible to decide to which
carbons the teft-butyl groups are attached. It is rea'sonable to assume that the proton
environment at 7.3 ppm is due to the hydrogen oftho to the oxygen that has an inductive pull
on electron density.
The 13C NMR spectrum has been partly assigned, but due to the presence of a large number
of weak lines due to quaternary carbons the assignment is incomplete. A 'H/13C correlation
was used to assist in the assignment of those carbons bearing protons - this enabled some of
the 13C peaks to be assigned (Table 4.3 and Figure 4.1) but some peaks still remain
unaSSigned.
Oc (ppm)
136.6
136.3
136.2
136.0
135.4
126.3
125.4
123.5
118.6
31.7
31.4
Table 4.3 Partial assignment of the 13C NMR spectrum of 146.
Multiplicity of
carbon signal
and J(3'p_13C)
s
d 10.6 Hz
d 8.4 Hz
m
d 18.1 Hz
d 19.0 Hz
m
m
s
s
OH (ppm)
8.8
8.2
9.1
8.2
7.7
7.7
7.3
7.1
1.2
1.5
Assignment
9
40r6
3
40r6
40r8
40r8
73
5 7 6
3~ 1
2 10
p p
Figure 4.1 Numbering scheme used in the assignment of NMR spectra of 146.
In the molecular structure of 146 (Figure 4.2 and Table 4.4) the phosphorus atoms are
stereocentres but the product was formed as a racemic mixture and no separation of the
enantiomers was attempted.
C(4) C(6)
Figure 4.2 Molecular structure of compound 146." 1
74
Table 4.4 Selected bond lengths (A) and angles (D) found in the molecular structure of 146'"
P{1 )-S{1) 1.S17(2)[1.S17{2)] P{1 )-S{2)-P{S) S7.21 (6)[S6.S7(6)]
P{1 )-S{2) 2.074(2)[2.082{2)] S{1 )-P{1 )-S{2) 1 OS.SO(8)[1 OS.83(8)]
P{S)-S{2) 2.087(2)[2.088{2)] S(1)-P{1)-C{1) 113.2{1 )[113.4{1)]
P{S)-S{S) 1.S05(2)[1.S02{2)] S{1 )-P{1 )-O{1) 112.1(1)[111.S{1)]
P(1)-O{1) 1.606(3)[1.607{3)] S(2)-P{1)-O{1) 1 06.5{ 1 )[1 06.6(1)]
P{S)-O{S) 1.607(3)[1.614{3)] S(2)-P{S)-S{S) 110.51 (8)[111 .38(7)]
P(1)-C{1) 1.817(4)[1.80S{4)] S{S)-P{S)-C{S) 11S.1(1)[118.5{1)]
P{S)-C{S) 1.783(4)[1.780{4)] S{S)-P{S)-O{S) 117.5(1)[118.1{1 )]
C(11)-O{1) 1.407(4)[1.403{4)] P{1 )-O{1 )-C{11) 130.0(2)[12S.8{2)]
C(16)-O{S) 1.40S(4)[1.410{4)] P{S)-O{S)-C{16) 120.3(2)[11S.5{2)
O{1 )-P{1 )-C{1) 1 06.S(2)[1 06.6(2)]
Mean P-O bond length 1.60S O{S)-P{S)-C{S) S8.0(2)[S8.2{2)]
N.B. The values in square brackets are those for the second independent molecule in the unit cell.
When the reaction of NpP2S, with catechol (142) was attempted, no soluble product was·
formed, it was assumed that an insoluble polymer formed. It is likely that the tert-butyl group
ortho to one of the hydroxyl groups reduces the reactivity of the substituted catechol as a
nucieophile. This steric effect is more likely to affect reactivity of the hydroxyl group in the
polymerisation than the in the ring closure reaction as the ring closure is intramolecular and
the polymerisation is intermolecular (Scheme 4.13).
Polymer?
s s s
oo~P::::s~P9
-:?' I "" ~ .,;:;
OH
OH
•
Scheme 4.13 Reaction of catechol and 3,5-di-tert-butylcatechol with NpP2S •.
75
When FC2P2S, was heated with 147 in toluene a mixture of three products was observed ( 31 p_
CH} NMR spectroscopy - singlets seen at 114,101 and 73 ppm), however when a hot dilute
solution of 147 in toluene was treated slowly with FC2P2S" pure 148 was obtained2• The op
value of 148 is in the range of the benzo-dioxaphospholane sulfides '07 and mass
spectroscopy confirms the presence of FCP(S)02C.H. (C,.H'3Fe02PS m/z 356). On standing
as a solid 148 undergoes a partial decomposition (possibly a hydrolysis reaction,o •. ,07) and
becomes dark green. Extraction of this green solid with petrol gives pure benzo-1,3,2-
dioxophospholane-2-ferrocenyl-2-sulfide 148 (Figure 4.3) which is not oxygen sensitive.
S 11 0
FC-P:;:J:g
148 Figure 4.3 P-Ferrocenyl benzo-dioxaphospholane sulfide.
The 13C-{'H} and 'H NMR spectra of 148 are more complex than expected and this may be
due to slow rotation about the P-C bond. If the ferrocenyl group is arranged in such a way that
the molecule is asymmetric then the lack of symmetry will cause 148 to have an increased
number of environments for both' Hand 13C NMR spectroscopy. A 13C/' H correlation was
obtained for 148. In the aromatic area more than two cross peaks were found. In the solution
state there are more chemical environments than would be expected for a symmetric
molecule. This increased complexity of the 'H and 13C_{'H} NMR spectra is also seen in the
spectra obtained for many other P-ferrocenyl compounds prepared in this thesis. Later in
section 5.6 these effects will be discussed in greater detail.
Lawesson's reagent analogues of 148 are known to react with oxygen nucleophiles to give
ring opened products, '07 however the spectacular hydrolysis of 148 where the iron atom is
freed from the ferrocenyl group was not expected. This can be explained by the iron co
ordinating to some ligand that is formed from 148 by the action of water. This ligand could then
remove an iron from a ferrocenyl group. This reaction is likely to create an intractable mixture
of iron complexes where the iron is co-ordinated to phosphorus oxygen sulfur ligands
(Scheme 4.14).
S 11 ...... 0
c~~ ·0 148
1
.. tOM Fc-P /
HO HO
FC-J~°-o OHO~
Possible ligand for iron
•
H
-Scheme 4.14 Hydrolysis of 148 to a ligand for iron.
76
This unexpected decomposition reaction may limit the use of compounds like 148 in further
synthetic work. For instance one of those compounds made from LR was ring opened by
methanol followed by O-methylation to give 149 and 150 (Scheme 4.15).'07
H \
Vo,c.:O
-
Me
..
/ " Then proton transfer Ph
3C 0) An
Me /
Ph3C,,©=0 0 S o '~~ o An
149 I Me
Me
VOO/S
+ 0 '~ Ph C 0 An
3 150 I Me
Scheme 4.15 Methanolysis and methylation of dioxaphospholane.
A crystal of 148 was obtained from a petrol solution. The molecular structure of 148 (Figure
4.4 and Table 4.5) allows a C20 2P and a C20 2P2S ring to be compared by
crystallography.29"" The average P-O bond length in 148 is 1.632(4) A, which is longer than
the average P-O bond length in 146 [1.609(3) Al. In 148 the phosphorus is bearing two
oxygen atoms, while in 146 each phosphorus has only one substituent oxygen atom so
increasing the electron density at the phosphorus atom in 146.
s Figure 4.4 Molecular structure of compound 148.29 77
Table 4.5 Selected bond lengths (A) and angles (0) in the molecular structure of 14829
P-0(1) 1.636(4) C(1)-0(1)-P 110.5(3)
P-0(2) 1.627(3) C(2)-0(2)-P 110.3(1)
P-S 1.893(2) 0(1 )-P-O(2) 95.2(2)
P-C 1.761(5) 0(1)-P-S 114.5(2)
C(1 )-0(1) 1.396(5) O(2)-P-S 117.0(2)
C(2)-O(2) 1.392(6) S-P-C 115.8(2)
C(1)-C(2) 1.373(7) 0(1)-P-C 105.6(2)
0(2)-P-C 106.2(2)
mean P-O distance 1.632 0(1)-C(1)-C(2) 111.1(5)
0(2)-C(2)-C(1) 112.5(5)
The molecule 148 is asymmetric, and due to arrangement of the ferrocenyl group, the plane of
the substituted Cp ring is at 85° to the C20 2P ring. The C20 2P ring is almost perfectly planar
(within 0.04 A) and co planar with the benzene ring.
The reaction of Fc,P,S. with 145 in toluene gives 4.6-di-tert-butylbenzo-1,3,2-
dioxaphospholane-2-ferrocenyl-2-sulfide (151) (Pure by 31 p-{'H} NMR spectroscopy 8p 113
ppm) (Equation 4.7),29 whose 31 p chemical shift is similar to that of 148 and the 1.3,2-
dioxaphosphole-2-sulfides made from LR. '07
Equation 4.7
The relative absence of phosphorus containing side-products in the synthesis of 151 is likely
to be due to the steric bulk of the tert-butyl groups which retard the formation of side products
such as polymers and 1 ,4,6,5,7-dioxathiadiphosphepanes (Scheme 4.16).
78
S S 11 S 11
Fc-P ............. P-Fc I \ o 0
..
-H,S
H 1
:0
SH
~ S""'I'Fc
o -H,S
Due 10 sleric effects
Scheme 4.16 Reaction 01 catechol (145) with lerrocenyl dithiophosphine ylide.
148 may be compared with P-Ierrocenyl cis-4,5-diphenyl 1,3,2-dithiaphosphole (152),
obtained by the reaction 01 Fc,P,S. and N-benzylidene benzylamine (153) (Scheme 4.17 and
Table 4.6). The details 01 the synthesis 01 152 will be described in Chapter 5.
©ro S o ~< ° Fc
148
PhXS S '-::::p,. Ph S/ ···Fc
152
S Fc, II
P-S I I S-P
II 'Fc S
Fc,P,S.
Scheme 4.17 Compounds 148, 152, and Fc,P,S •.
79
Table 4.6 Selected data for 148,152, and Fc,P,S •.
Property unit 148
u(PS) (cm") a
15 31 p (ppm) 113
Redox potential (volts) 0.80b
endocyclic P-E bond length (A) 1.64
• It was not possible to clearly identify the PS stretching vibration.
b was measured for 151.
C was measured for 12.
d is an average for the two endocyclic P-S bond lengths.
152
670
86.3
0.71
2.09
FC,P,S.
670
16.9c
0.52c
2.12d
The higher electronegativity of the oxygen atoms will give them a greater inductive pull on the
electron density at the phosphorus atom. This results in the redox potentials of 152 and 12
being lower than that of 151. Besides oxygen having a higher electronegativity than sulfur, the
oxygen in 148 is bonded to an aromatic ring. Aromatic rings have a strong resonance electron
withdrawing effect on oxygen atoms bonded to them, whereas the sulfur atoms in 152 are
bonded to benzylic carbons where such an electronic effect is absent.
80
Section 4.3, Experimental
Synthesis of 148
Catechol (147) (1.3 g. 11.8 mmol) was placed in a flask with toluene (200 ml). The flask was
fitted with a soxhlet head containing a thimble with FC2P2S, (3.19 g. 5.69 mmol) inside it. The
flask was heated so that the FC2P2S. was extracted until the extract was no longer coloured.
After evaporation of most of the toluene, petrol (100 ml) was added and the mixture filtered, to
remove a green solid, giving an orange solution. After removal of solvent, crude 148 was
obtained as an orange solid. The orange solid was stored in a flask in a freezer. It changed to
dark green on storage, and the green solid was extracted with dry hexane. This extract was
filtered through a pad of AI20 3 (Active basic Brockmann grade I) or Si02 (flash column grade
may be used) and the solvent removed in vacuo to give 148 as an yellow/orange solid (134
mg. 2.8 mmol. 24%).IR 3095w, 1478s, 1412m, 1390m, 1366w, 1350w, 1230s, 1188s, 1106m,
1095m, 1028s, 1009m, 1002m, 924w, 903m, 858s, 837s, 815m, 780m, 770m, 741s, 710s,
606m, 540m, 495m, and 479m (cm·'). op 113 ppm. OH (ppm) 7.1 (3 H, m), 6.8 (1 H, m), 4.54
(m), 4.53 (m), 4.4 (m), 4.2 (s) Total integration for 4.5 to 4.2 ppm (9 H). Oc (ppm) 123.2,
122.4(quat), 116.0, 112.4, 72.7 (m), 70.9 and 67.8. 13C/'H Correlation OH (ppm) [oc (ppm») 7.1
[123.2), 6.8 [116.0), 7.1 [112.4), 4.54 [73.053), 3.53 [72.825), 5.54 [72.625), 4.53 [72.344), 4.4
[70.9) and 4.2 [67.8]. MS(EI+) mlz 356 (M+), 291 (M-Cpt, 290, 186, 139, 121, 69 and 56.
molecular ion at 355.9741amu 12C'6'H'3Fe'"0;'p32S2 requires 355.97228 amu (5.1 ppm
error), the isotopic distribution was found to be the same as predicted.
Synthesis of 151
145 (0.53g. 2.3 mmol) was reacted with FC2P2S, (0.63g. 2.3 mmol) in toluene (50 ml) in a
similar manner to the above reaction. The reaction mixture was cooled to -18C overnight and
the product crystallised. The compound was recrystallized from petrol (to remove residual di
t-butylcatechol) to give 151 an orange solid (0.225g. 0.48 mmol. 21 %). On standing this solid
darkened to brown. IR 1720w, 1655w, 1624m, 1588m, 1561w, 1519w, 14855, 1466m, 1446m,
1312s, 1392m, 1365m, 1352w, 1319m, 1283m, 1264m, 1228s, 1188s, 1153m, 1089m,
1051w, 1026s, 1004m, 975s, 935w, 903m, 860vs, 8225, 804m, 788s, 736s, 706s, 635m,
643m, 623w, 594m, 536w, 526w, 493s, 445m, 419w, 410w, 343w, and 323w (cm·'). op 113
ppm. OH (ppm), 7.0(3 H, m), 4.65-4.45 (m) and 4.4 (s) Integration for 4.6 to 4.4 ppm is 9H, 1.45
(16 H, s), 1.30 (15 H, s). MS(EI+) mlz 468(M+), 403,316,267,217,186,155,113,70,51,41
and 31. Molecular ion found at 468.0976 amu [12C2.'H29'60,s"Fe31p32S2 requires 468.09748
amu (0.3 ppm error)]. CV: Reversible redox couple at 0.80 volt relative to a SCE.
81
The reaction of NpP2S4 with 145
NpP2S4 (0.5g) and 145 were placed in toluene (20 ml) and this mixture heated to 100C for five
days, during this time about half of the toluene evaporated off. After cooling, the mixture was
stirred to cause the precipitation of a white solid which was collected by filtration and washed
with hexane (10 ml) and allowed to dry to give 146 as a white solid. IR 3005w, 29605, 2906m,
2868m, 1606w, 1581m, 1557w, 1495m, 1478m, 1460sh, 1445m, 14105, 1395sh, 1365m,
1345w, 1326w, 13025, 1261w, 12245, 1213sh, 1201sh,1160m, 1101m, 1027w, 1003w, 9815,
9205, 9035, 8845, 873sh, 837m, 825m, 795m, 775w, 769w, 7595, 7485, 704w, 6785, 6635,
6525, 636m, 616w, 5965, 571w, 554w, 537w, 518w, 507m, 490m, 474m, 455w, 423m, 390w,
371w, 322w, 303w (cm-'). op (ppm), 74.4 d, 71.2 d 2J[31 p _31 P1=3.2 Hz. OH (ppm) 9.1 [ddd,
4J('H-'H)=1 Hz, 3J('H-'H)=7 Hz, 3J['H-31 p1=22 Hz]. 8.8 [1 H, ddd, 4J('H-'H)=2 Hz, 3J(1H-'H)=7
Hz, 3 J('H-31 p)=24 Hz]. 8.2 (2 H, m), 7.7 (2 H, m), 7.3 (m) and 7.1 (m) (Integration together of 2
H), 1.5 (9 H, s), 1.2 (9 H, 5).
Table 4.7 'H-{'H) experiments performed on 146.
irradiated peak o(ppm) changed peak(s) o(ppm)
9.1
8.8
8.2
7.7
7.7 The downfield side of this peak is simplified.
7.7 The upfield side of this peak is simplified.
7.7 This peak becomes slightly .more simple in appearance.
The peaks at 9.1 and 8.8 change to doublets of doublets and the
peak at 8.2 changes to a pair of singlets.
oe (ppm), 149.1 (m, quat), 142.7 (dd, 5.3 Hz and 2.5 Hz, quat), 141.2 (dd, 18.3 Hz and 4.8
Hz, quat), 139.4 (dd, 12.5 Hz and 3.8 Hz, quat), 136.3, 136.2 (d, 10.6 Hz), 136.0 (d, 8.4 Hz),
135.4 m, 133.9 (quat, impurity), 133.7 (t, 12.3 Hz, quat), 132.8 (d, 3.6 Hz, quat), 129.6 (t, 8.8
Hz, quat), 127.4 (dd, 114 Hz and 2.7 Hz, quat), 126.3 (d, 18.1 Hz), 125.4 (d, 19.0 Hz), 123.5
(m), 118.6 (m). 35.8 (quat), 35.2 (quat), 31.7, and 31.4. 13C/'H correlation 'H o(ppm) [13C
o(ppm)]. 8.2 [136.5]. 9.1 [136.2]. 8.8 [136.61, 8.2 [135.4]. 7.7 [126.21, 7.7 [125.41, 7.3 [123.21,
7.1 [118.61, 1.2 [31.7]. and 1.5 [31.41. MS(EI) (m/z) 504, 489, 440, 251, 221,189,157,119,91,
57, 41, and 29. Molecular ion measured 504.0577 amu, 12C'4'H,.'·O,31 p,32S3 requires
504.05701.
82
Chapter 5 The Reaction of Dithiadiphosphetane Disulfides with Dienes,
Alkenes and Thioaldehydes
Section 5.1 Introduction to Organo Sulfur Phosphorus Rings
The reaction of dithiadiphosphetane disulfides (R2P2S.) with alkenes has been used in the
synthesis of antisludge agents 154 and 155 for use in engine oils'12 (Scheme 5.1), R' may be
a variety of alkyl and aryl groups including phenyl, tert-butyl. and straight chain alkyl groups. R
can be Me. An, and 3,5-di-t-butyl-4-hydroxyphenyl.
R~ R' R'
~s ~s 11 11 ~-R P-R
R2P2S4 • + I 6 /S /S
P~ R/P~S R/ "S
154 155
Scheme 5.1 Synthesis of engine oil/fuel additives from dithiadiphosphetane disulfides and
alkenes.
The formation of 154 and 155 could proceed via pericyclic reactions (Scheme 5.2). The
reaction could start with a [2+2] cycloaddition between the dithiophosphine ylide and the
alkene followed by a rearrangement to give an alkene, after another [2+2] cycloaddition and
rearrangement. Hydrogen sulfide could be eliminated to give 154 and 155. Alternatively the
reaction could be via a pair of ene reactions followed by the ring closure (e) (Scheme 5.2).
~s + ~p'l'
I R
~ ene f \reaction R'
R'
II Y:; s
HS1'R
RPS2 12+21 -c ~
s 5 rfl I I'R
R-P HS 11
~PS2
gena reaction
s d 1 Reamlngement
RY" R R'Y' R / / e P-SH P-SH
154 + 155 -4--- M + ~ -H2S P-SH P-SH
R/II R/II s s
Scheme 5.2 A possible mechanism for the synthesis of the additives.
83
Pericyclic reactions have been used to trap a variety of reactive species as stable adducts.
Both Diels-Alder and [2+2] reactions have been used to trap reactive intermediates. For
example dichloroketene (156) can be trapped as [2+2] adducts with alkenes'14 while
thionitrosoarenes have been trapped with 1 ,3-dienes as the Diels-Alder adducts (157) also the
ene reaction product (158) was formed (Scheme 5.3 and Table 5.1 )."5 Interestingly for more
electron-poor thionitrosoarenes the ene reaction was favoured over the Diels-Alder."5
~0 ° O:J ctr( Cl r:::"" ,1 Cl 'y • d Cl
° Cl Cl
156 25% Cl 23% 10
H WO Cl
H Cl 77%
X Ar,(x Ar-N • , "yl \\ Ar/~'S S 157 158
Djels~Alder Ene reaction reaction product product
Scheme 5.3 Diels-Alder and ene reactions of thionitrosoarenes, and [2+2} reactions of
dichloroketene."·,"5
Table 5.1 Diels-Alder and ene reactions of thionitroso compounds."5
Ar Yield (%) Ratio of Diels-Alder to ene reaction adducts (157:158)
Diels-Alder ene product (157) product (158)
An 55 10 85:15
p-Tolyl 33 22 60:40
Ph 30 25 55:45
1-Naphthyl 29 36 45:55
p-BrCsH. 13 38 25:75
p-CICsH. 14 41 25:75
3-Pyridyl 14 41 25:75
P-0 2NCsH• 9 36 20:80
84
1. Sigmatropic rearrangement: While one a bond is formed another is broken and a 1t bond
migrates. An example of this reaction would be the rearrangement of sulfur ylides containing
an allyl group (159) to a homo-allyl sulfide (160) (Scheme 5.4)."6
- o /
159 160 Scheme 5.4 Rearrangement of as-allyl sulfur ylide into a homo-allyl sulfide.'15
2. Cycloaddition (and cycloelimination): Two a-bonds are formed at the same time as two
1t-bonds are broken. An example of this reaction would be the conversion of two molecules of
an alkene into a cyclobutane. While the thermal [2+2] cycloaddition of alkenes is unlikely as it
is thermodynamically disfavoured. the mechanism of such a reaction will be considered
(Scheme 5.5).
LUM~
HOM~
..
Bond rotation needed in one molecule to allow the HOMOs to overlap with LUMOs
Scheme 5.5 Thermal dimerisation reaction of two molecules of cis-but-2-ene.
One of the alkenes reacts such that rotation occurs about the carbon-carbon double bond.
This alkene is reacting antarafacialy, while for the other alkene this rotation does not occur,
this alkene is reacting suprafacialy (Figure 5.1). The reaction is going via a MObius transition
state.
suprafacial
antarafacial 85
Figure 5.1 A 21ts+21ta reaction between two alkenes.
If a reaction is a pericyclic reaction, then it will go via either a HOckel or a MOblus transition
state, and a set of rules exists as to which transition state, will be allowed on symmetry
grounds (Table 5.2). These rules are based on the Hofmann-Woodward rules, which are
'A ground-state pericyC/ic change is symmetry-allowed when the total number of (4q+2)
supra facial and 4r antarafacial components is odd. ,117
[(4q+2) and 4r refer to the number of electrons involved in forming the transition state, and q
and r can be zero or integers]
For a thermal reaction if the planar Hiickel transition state has 4n+2 electrons in it then it will
be aromatic and stabilised, while if it contains 4n electrons it is destabilised because it is
antiaromatic. By introd ucing a twist and becoming a MObius transition state antiaromaticity is
avoided. The pericyclic reaction will go via the most stable transition state. Again this rule is
reversed for photochemical reactions.
Table 5.2 Summary of the symmetry selection rules for pericyclic reactions.
Number of electrons Reaction conditions Symmetry permitted transition state
4n 1! electrons Thermal MObius
4n 1! electrons Photochemical Hiickel
4n+2 1t electrons Thermal Hiickel
4n+2 1t electrons Photochemical MObius
If the reaction mixture is irradiated with UV light, the cyclobutane formed will have a different
geometry. In neither molecule will there be rotation about the carbon carbon double bond as
the reaction occurs. Instead the two molecules tip towards each other allowing the orbitals to
overlap. Then the molecular orbitals of the cyclobutane are formed. The cyclobutane formed
will be in an excited state, but after loss of energy it will descend to the electronic ground
state. As the alkenes have two sides they can approach each other in two ways.
3. Electrocyclic: A polyene is isomerized to or from a cyclic isomer, this reaction has similar
rules controlling the stereochemistry of the products as to those controlling the other pericyclic
reactions (Scheme 5.6).
86
y ~ns y
I~ 'I le::: ~ ( c ~ +
'I
cis
ex Irans,lrans cis,cis
lrans
Scheme 5.6 Ring opening of cis-1,2-dimethylcyclobut-3-ene and ring closure of octa-2,4,6-triene.
The reason for examining the reactions of alkenes with the dithiadiphosphetane disulfides was
to explore the reactivity of the sulfur phosphorus compounds further, including the mechanism
of the reaction with alkenes and to form new compounds that could have some useful action,
such as additives for engine oil.
Section 5.2 2+2 Cycloaddition Reactions of Dithiadiphosphetane Disulfides and Alkenes.
The reaction of electron rich alkynes with dithiadiphosphetane disulfides is known to give
thiaphosphorines (161) (Scheme 5.7)"8.119
S \\
:;;;;.==""- P=S
1 S R" \\ /
R''!: "'i ~'
R' : :
R' P R'
~XSXN~ ..
161
•
1
Scheme 5.7 Reaction of dithiadiphosphetane disulfides with electron-rich alkynes.
87
Scheme 5.7 contains a possible mechanism for this reaction. The first step is a [2+2]
cycloaddition reaction that would give a thiaphosphete ring that would suffer much greater ring
strain than the saturated thiaphosphetane rings prepared in this chapter (Scheme 5.8).
S 11
R-~JI
S 11
R-~~
Scheme 5.8 Thiaphosphete and thiaphosphetane rings.
Norbornadiene (bicyclo-[2.2.1]-hepta-2,5-diene) (162) was selected as a possible substrate for
reaction with dithiadiphosphetane disulfides. The ring strain present was expected to increase
the reactivity of the C=C double bonds, this alkene is a diene where the molecule is held in
such a way that a homo-Diels-Alder reaction has the potential to occur. Examples of
heterodienophiles, such as silenes, reacting with 162 to form homo-Diels-Alder adducts (163)
are known (Scheme 5.9).'20
tauLi •
©OOJ tauLi! tb.
Scheme 5.9 Formation and cycloaddition reactions of a silene.
The reaction of 162 with FC2P2S, for 16 hours at ca 80°C was found to give 43 [op 64 ppm,
u(P=S) 632 cm"] as a racemic mixture (Equation 5.1 )'21 No attempt was made to separate
the enantiomers or to devise a stereoselective synthesis. 43 was formulated by 13C-{' H} and
'H NMR spectroscopy as the tricyclo product (thiaphosphetane) formed by the [2+2] reaction
of the alkene with a dithiophosphine ylide.
..
162
H S
l({1=l-FC H
43
Equation 5. 1
88
While exo [2+2J cycloadditions to norbornadiene are well known, the possibility of either an
endo [2+2J cycloaddition or a Homo-Diels-Alder reaction followed by a rearrangement could
not be discounted. Both of the latter reactions would give an endo product. To discount these
possibilities the compound was examined by X-Ray crystallography. In the solid state 43
(Figure 5.2 and Table 5.3) exists as the exo isomer 121 The P-S bond length [S(2)-P(1)J is
shorter than the mean of the two P-S bond lengths in FC2P2S, [2.118(4.2) A], and the P-S
distance in 43 is approximately the same as the sum of the covalent radi '22 The P=S bond
length is not significantly different to that in FC2P2S. [1.930(3) AJ. The P(1 )-S(2)-C(11) and
S(2)-P(1)-C(16) angles are smaller than angles P(1)-S(1)-P(1*) and S(1)-P(1)-S(1*) in
FC2P2S •.. Both the P(1)-C(16)-C(11) and S(2)-C(11)-C(16) angles are greater than 90°. The
difference in the angles at the phosphorus and sulfur atoms between 43 and FC2P2S. is
because bond C(11)-C(16) is shorter than P(1)-S(2), hence distorting the ring away from a
square geometry. The thiaphosphetane ring is close to planar with S(2) being only 0.1 A away
from the plane described by P(1), C(11) and C(16).
Table 5.3 Selected bond lengths (A) and angles (0) in the molecular structure of 43.
S(1)-P(1) 1.940(2) S(1 )-P(1 )-S(2) 122.0(1)
S(2)-C(11 ) 1.850(6) P(1 )-S(2)-C(11) 80.1(2)
P(1)-C(16) 1.847(6) S(1 )-P(1 )-C(1) 114.1(2)
C(11 )-C(16) 1.585(7) S(2)-P(1 )-C(16) 83.8(2)
S(2)-P(1 ) 2.102(2) S(2)-C(11 )-C(16) 100.3(4)
P(1)-C(1) 1.800(6) P(1 )-C(16)-C(11) 95.7(4)
89
This reaction was repeated using the more soluble dithiadiphosphetane disulfide (12) in COCI3
at room temperature. Within 14 hours all the starting material was consumed and the [2+2]
adduct was formed.
The reaction could be a (21<s+21<a) cycloaddition reaction (Scheme 5.10), the bicyclic alkene
cannot be the antarafacial component on geometry grounds. Due to the lack of groups bonded
to the sulfur it is impossible to verify the antarafacial nature of this reactant. The presence of
the sulfur and phosphorus in the four membered ring causes it to be more stable than a
cyclobutane ring would be, because the effects of ring strain are less strongly experienced for
rings which contain the heavier elements.
RPS2
Alkene _f~) ~ond~ _11
t~,_ LUMO
LUMO
_11 ~ • ~ _11
Rotation about a P-S HOMO bond
Non-bonding
_11
t~, _llf W) ~ond~ 11
HOMO
Scheme 5.10 Orbitals taking part in the formation of 43.
An alternative mechanism (Scheme 5.11) in which the dithiophosphine ylide reacts as a 1,3-
dipole with the alkene, before a rearrangement then forms 43 as the product, can be
discounted for the following two reasons. Firstly the distance between the two sulfur atoms is
likely to be too great for them both to approach the different ends of the alkene and secondly
the initial step reduces a phosphorus (V) to a phosphorus (Ill) compound. In this alternative
mechanism the reacting MOs are the frontier orbitals (Scheme 5.12). A second alternative
mechanism which would be more reasonable is the attack of the dithiophopshine ylide as an
electrophile on the alkene (Scheme 5.12).
90
Scheme 5.11 Alternative mechanisms for the formation of 43.
H H Anti-bonding
~U ~ -.
LUMO
LUMO
._1l W HOMO
HOMO
H H Bonding
1l
~U Scheme 5.12 MOs that would be interacting in the first alternative reaction mechanism.
Using the COSY spectrum (Figure 5.3) the majority of the proton NMR spectrum of 43 can be
assigned. By starting at the cross peak at 6.15/3.27 ppm (DB) the bridge head proton on one
side of the bicyclic system can be identified (Figure 5.3). The next strong cross peak that is
3.28/2.97 shows the coupling to the protons on carbon 9. A very strong cross peak exists at
2.97/1.70 (AB) that is for the germinal coupling. Cross peaks can be observed at 3.13/1.70
(AB) and 3.08/1.70 (AB). these are due to a long ranged coupling between the
thiaphosphetane protons (Atoms 2 and 5) and proton 9a. The most important fact that can be
observed in the 'HI13C correlation is the identification of the carbons that are in the
thiaphosphetane ring.
91
2.0
'------+~ .... _II_ 3.0
B
4.0
1--1-----+----,--+----+-----+---11- 5.0
I i i 5.0 4.0 3.0
Figure 5.3 'H-'H COSY spectrum of 43.
j
2.0
6.0
This expanded area (2.8 to 3.4 pp m) (Figure 5.4) of the COSY spectrum is cluttered, so it is
not possible to exclude the possibility of a weak interaction between the other proton on atom
9 and the protons on atoms 2 and 5. The 'H and 13C assignments for 43 are shown in Figure
5.5.
AB
<>
BC AC
Figure 5.4 Expansion of 'H-'H COSY spectrum of43. 92
Key A is proton 9.
B is protons 1,2 and 5.
e is proton 6.
Atom numbers 1H 13C
9a 1.7 H
9 H 3.0
6'2H~ 6 136.5
1 47.2
135.9 H 6.1 H 8 3.1
S
4U / "---Fe
2 3H
1 S 3
36.4
H 3.1
Figure 5.5 Atom numbering with 'H and 13e NMR spectroscopy assignments for 43.
When the 'H NMR spectrum of 43 was recorded in D. toluene, the different environments due
to the alkyl portion of the molecule were spread over a wider range of chemical shifts. While
the signals due to the protons on carbon 9 and carbon 1 (or 6) are well separated from the
signals of the protons on carbons 2 and 5 (The thiaphosphetane ring), these signals are very
close to each other and another proton signal. Even with the resonances spread over a wider
frequency range, the thiaphosphetane protons can not be resolved clearly. Shown below as
an insert, is part of a 'H spectrum obtained from a double irradiation experiment identifying the
geminal coupling between the protons on atom 9 (Figure 5.6).
~ A I
'---"' -J j j I J
6.0 5.5 5.0 4.5 4.0 j j I
3.5 3.0 2.5 ,
2.0 ,
1.5 1'0 1H Chemical shift o(ppm)
Figure 5.6 'H NMR spectrum of 43 (In D.-toluene), showing effect of irradiation at 1.5 ppm.
93
The 'H-'H COSY spectrum (D,-toluene), allows much of the 10 spectra to be understood, and
suggests that the two thiaphosphetane proton environments are coincidental (Figure 5.7).
f pp.
FC
f 5
D
I DE
f •
FC
, 3
, FB
\ 2
Figure 5.7 'H COSY spectrum of 43 recorded in D,-toluene.
Compound 43 was found by cyclic voltammetry to undergo a single reversible redox change in
the region 0 to 1.3 Volt (Figure 5.8) as expected for a simple ferrocene compound.
1.3 E (V) 1.0 0.8 0.6 0.4 0.2 Figure 5.8 Cyclic voltammogram for 43.
'" 5 " " •
94
The formation of 43 is likely to be the most straightforward synthesis of the 1,2-
thiaphosphetane ring, though 164 can be prepared by two routes using a sulfur halide or a bis
TMS sulfide (Scheme 5.13).123
F F
~ MePCI2
Me3Si S, ~ 's SiMe3 -2Me3SiCI
F F -1960 C to RT Ether
S 11
R-P-S
FgF F 164 F
RP(SiMe3b •
-2Me3SiCI -780 C to RT
Ether
F F
J.. ~SCI CIS' A
FF
R= Me, tert-butyl, Ph and 2,4,6-tri-tert-butylphenyl
Scheme 5.13 Thiaphosphetane sulfides formed by the rearrangement of dithiaphospholes.
These thiaphosphetane sulfides are thought to be forming by the rearrangement of the five
membered heterocycle (165) (dithiaphospholane) (Figure 5.9).'23 When an attempt was made
to form the arsenic analogue, the rearrangement of the five-membered heterocycle (166) to
the four membered ring did not occur.'23.'2.
R
~ S/ "S
FKF F 165 F
Figure 5.9 A dithiaphospholane.
The presence of the fluorine atoms is likely to encourage the ring contraction - when ethane-
1,2-dithiol is reacted with bis-dichlorophosphines, bis-dithiaphospholanes (167) were formed
(Equation 5.2).'25
Cl ........ /x-.... /CI P P 1 I Equation 5.2 Cl Cl
X can be CH 2 or NMe 167 >70%
The oxygen heterocycle (168) was obtained using a similar route, as the rearrangement is
likely to be thermodynamically favoured (ca. 150 KJ mor' based on bond enthalpies) a kinetic
barrier must be present (Equation 5.3).'03.'25
Cl ........ /x-.... /CI P P I I Equation 5.3 Cl Cl
X can be CH2 or NMe 168 40%
95
By treatment of an ester (169) with P.SlO (P,Ss) a thiaphosphetane (170) was formed which
then rearranged to give a oxaphosphetane (171) (Scheme 5.14).126
~s
R 11 'N P-SR'
I I H c:? S
o 170
R-.....~~ H COOR'
169
! Rearrangeme
R'N~W_SR' I I H c:? 0
S 171 Scheme 5.14 Formation of a Oxaphosphetane (171) via a Thiaphosphetane (170).
The carbonyl and alkene groups are likely to increase the ring strain in 170 so favouring the
ring opening that is assumed to be part of the rearrangement.
The thiaphosphetane (172) has been detected by 31p NMR spectroscopy lop -39 ppm in (06)
toluene)] as a product of the reaction of thiobenzophenone with Ph3PCH, (Scheme 5.15)127
172 was an unstable compound that decomposed above _20°C.127 Under identical conditions
from benzophenone the oxaphosphetane (op -67 pp m) was obatined. 127 Careful warming was
reported to cause formation of triphenyl phosphine and 1, 1-diphenylthiirane (1, 1-diphenyl
thioepoxide) which decomposed at OOC to give triphenyl phosphine sulfide and 1,1-
diphenylethene (118).127
Ph,CS + Ph3P=CH,
Ph ph 1/ S-P-Ph
Ph-t-J
Ph 172
PhJlph + Ph3PS
-200C - + Ph3P
Scheme 5.15 Formation and decomposition of a thiaphosphetane from a thioketone and a
phosphorus ylide. 127
96
When 172 was treated with 1 equivalent of Ph3P= "CH2 before being allowed to warm up, the
"c label did not appear in the alkene that was formed (Scheme 5.16).127 This suggests that
the formation of the thiaphosphetane (172) from the thione and the ylide is irreversible and the
formation of the thiirane is by an intramolecular mechanism.'2'
x ..
Mechanism not responsible
..
Scheme 5.16 Alternative fragmentation mechanism.
The mechanism responsible for the formation of the thiirane and the triphenylphosphine is
likely to be either cleavage of the phosphorus sulfur or phosphorus carbon bond. Cleavage of
the weaker phosphorus sulfur bond is more likely to be occurring (Scheme 5.17).
Ph ph 1/ S-P-Ph
Ph-t--J~ Ph
Scheme 5.17 Formation of the thioepoxide from the thiaphosphetane.
If such a ring opening reaction was to occur for 43, then the rigid shape of the molecule would
hold the molecule in such a way that the formation of the thiirane would be impossible. Also
97
formation of a molecule of RPS would be unfavourable as the energy barrier for a
decomposition via a RPS species (phosphinidene sulfide) would be extremely high (Scheme
5.18).
-
Geometry is wrong for thiirane formation
Scheme 5.18 Hypothetical mechanism for the fragmentation of 43.
The alternative route to the thiirane via carbon phosphorus bond cleavage would require the
formation of a very unstable carbanion, the geometry of the molecule would be better for the
formation of the thiirane if the anion would form. However the required formation of a very
unstable anion intermediate should be sufficient to prevent this reaction (Scheme 5.19).
• -
~ Very unstable carboanion l' required as an intermediat
10s+ Scheme 5.19 Second hypothetical mechanism for the fragmentation of 43.
The reaction of LR with 162 gave a white solid (Equation 5.4), recrystallized firstly from ethyl
acetate and then from CH,Ci:,/ether to obtain a pure sample of 173 (op 62.6 ppm).
.. 01:~ P-An 's
~
Equation 5.4 LR
98
Similarly the reaction of 14 with 162 gave 174 (op 63.9 ppm) (Equation 5.5), which was very
soluble in most organic solvents.
• M;IT P-R 's
~ Equation 5.5
n-BuO =R
It is likely that by adding alkyl groups to the bicyclo-[2,2,1]-heptane portion of the molecule
would be likely to increase the solubility of the organo sulfur phosphorus products by making
the compounds less crystalline. For instance the reaction of methylcyclopentadiene with
ethylene would give a mixture of methylnorbornenes that would be less likely to give
crystalline products.
To investigate the scope of the reaction, norbornene (175) was reacted with Fc2P2S,. This
gave a low yield of a waxy orange solid (176) (op 66.4 pp m) (Equation 5.6) formed by a [2+2]
reaction of the alkene with the dithiophosphine ylide.
l\ J:-FC ~s
Equation 5.6
175 176
It had been hoped that NOE experiments could reveal whether the exo or endo isomer was
produced. Sadly the expected NOE effect could not be found. This might be because several
of the proton environments are overlapping. The COSY spectrum of 176 (Figure 5.10) clearly
shows how congested the 'H spectrum is.
99
~ 1. BB
\ I. 59
\ I 2.88 I
~ "" !pC
~ 2.513
~
3.9"
<.~
3.5"
~}-----+---~~----4-----~-----+-----+----~----~.~4.00
~L--+ ____ ~ ____ ~~ ____ }-____ +-____ +-____ +~4.S.
~~----}-----+-----+-----4-----~-----+-----+-----+~5.0.
z. BB 1.
Figure 5.10 'H-'H COSY spectrum for 176.
Cross peak AE is due to the long range coupling between the proton on carbon 9 facing
towards the phosphorus sulfur part of the molecule and the endo protons on the carbons 7
and 8. The assignment of the NMR spectra is shown in Fig 5.11.
Atom numbers 1H
1.55 H 9 H 3.06
13C 38.3
S 114 P
1.7 H 7 5 / ~F 63.2 3.4 C H
2 S3 41.6
3.5 Figure 5.11 Atom numbering, proton and carbon assignments.
100
The extremely complex nature of the peaks prevented measurement of the 'H-'H coupling
constants, double irradiation could not be used for spectral simplification. In the 'H COSY
spectrum cross peaks from 3.1 to 1.1 ppm and 1.6 to 3.4/3.5 were clearly seen. The presence
of these peaks is consistent with the exo isomer as a long ranged coupling between the endo
protons and the proton bonded to carbon 7 on the opposite side to the endo protons in
question is often found. Similar cross peaks are present in the 'H COSY spectrum for 43 that
agrees with the crystallographic result for 43. The diagram below show the long range
coupling which is found in the rigid bicyclic system. The bonds through which the coupling
effect occurs are the bold lines (Figure 5.12).
H
Figure 5.12 Long range 4J coupling in bicyclo[2.2.1]heptane (Norbornane) systems.
The mass spectrum (El) for 176 showed a strong molecular ion (m/z=374) as did the other
thiaphosphetanes formed from norbornadiene/norbornene. Also present was a peak at 280
amu, which is due to the ion (FcPS2), a [2+2] cycloelimination is one possible fragmentation
that could be responsible for presence of this ion.
It was found that cyclohexene does not react with FC2P254 under similar conditions,
suggesting that only ring strained alkenes can react under these mild conditions. To continue
the study, hexamethyl dewarbenzene (177) was reacted with FC2P254. This reaction (Equation
5.7) gave under mild conditions a moderate yield of a tricyclo product (44) [u(P=S) 694 cm-']
with recovery of Fc2P25 4.'2'
177 .. S 11
:r--+---l-P-Fc I
Y--t-----5-S
44
Equation 5.7
101
The 3'P-{'H} NMR spectrum of 44 is a singlet (op 68.4 ppm) as expected and the 'H NMR
spectrum contains six peaks due to the methyl groups. Because dewar benzene (177) has all
carbons substituted with methyl groups very little information about the structure can be
obtained from the 'H NMR spectrum. The 13C-{'H} NMR spectrum clearly shows the presence
of two alkene environments at 146.4 and 140.1 ppm, ruling out the possibility of a homo
Diels-Alder reaction (Figure 5.13).
i I , 1 i I
140 120 100 80 60 40 13C Chemical shift (ppm)
Figure 5.13 The partial 13C-{'H} spectrum of 44.
The two remaining structures that were most likely are those formed in a [2+2] reaction
between hexamethyldewar benzene (177) and a P-ferrocenyl dithiophosphine ylide. In
common with the formation of 43, this reaction could give either the exo or endo isomer. Also
even with an exo or endo structure there are two possible isomers that could form. This is
because the phosphorus atom is tetrahedral, so the sulfur atom and the ferrocenyl group
could be arranged in two different ways, (Scheme 5.20).
To resolve the confusion over the exact structure of the compound a crystal of 44 was grown
from a CDCI3 solution. Single crystal X-ray crystallography revealed the compound to be the
exo isomer (Figure 5.14 Table 5.4)'21 Like 43, 44 was formed as a racemic mixture'21
Fe I p=s 's
Scheme 5.20 Different isomers possible for 44.
102
~J ~\ Fe1
'J Figure 5,14 Molecular structure of compound 44. '2'
Table 5.4 Selected bond lengths (A) and angles (0) found in the molecular structure of 44. '2'
S(1)-P(1) 1.931(1) P(1)-S(2)-C(12) 79.9(1)
S(2)-P(1 ) 2.095(1) S(2)-P(1)-C(11) 83.7(1 )
S(2)-C(12) 1.880(3) S(2)-C(12)-C(11) 98.5(2)
P(1)-C(1) 1.785(4) P(1 )-C( 11 )-C(12) 96.0(2)
P(1)-C(11) 1.844(4) C(11)-P(1)-S(1) 122.4(1)
C(11)-C(12) 1.588(4) S(1)-P(1)-S(2) 122.9(1)
S(1 ) ... C(22) 3.45
S(1 ) ... H(22a) 4.25
S(1) ... H(22b) 2.71
S(1) ... H(22c) 3.60
The thiaphosphetane ring is much less planar than that in 43, S(2) is 1.3 A above the plane
made by P(1), C(11) and C(12). This can be explained by the steric repulsion between the
S(1) and a nearby methyl group (C22) pushing the ring away from being planar. The P(1)
S(2)-C(12) angle is similar [at 79.9°] to the corresponding angle in 43 (80.1°), while the torsion
angle P(1)-C(11)-C(12)-S(2) is greater at 44° than the corresponding angle in 43 [P(1)-C(16)
C(11)-S(2) which is 4°]. Angle C(11)-P(1)-S(1) is larger than the corresponding angle in 43,
this is likely to be due to the steric effect of the methyl group (C22) (Figure 5.15). While the
S(1 )-P(1 )-S(2) angle is not significantly different to the corresponding angle in 43, The C-S
distance is lower than that found in 43. Like 43 the exocyclic sulfur atom is on the exo side of
the molecule. The phosphorus sulfur bond lengths in the ring are not significantly different to
those in 43.
103
Stenc repulsion
S
U-Fc
's
Figure 5.15 Steric repulsion influencing the C,PS ring.
Although compound 44 was an exo product because a recrystallization was performed before
spectroscopic examination of the products, it is impossible to prove that none of the endo
isomer was formed. When an attempt was made to increase the yield of 44 by repeating the
reaction at a higher temperature and increasing the time used, an intractable mixture was
formed. This suggests that at the higher temperatures several competing reactions are all in
operation. This [2+2] cycloaddition is in stark contrast to the homo-Diels-Alder reaction that
occurred between tetracyano ethylene and hexamethyl dewar benzene (Equation 5.8), the
reason for the difference in reactivity is unclear.128
Equation 5.8
CN CN
The cycloaddition chemistry of the dithiophosphine ylide from Fc,P,S4 has some differences
and similarities to the cycloaddition of dichloroketene (156). Dichloroketene is known to give
[2+2] cycloaddition adducts with straight chain 1,3-dienes and cyclopentadiene, and also it is
known to give in low yields cycloaddition adducts with alkenes such as norbornene and
norbornadiene. '14
One possible reason for the formation of [2+2] cycloaddition adducts, instead of the Diels
Alder adducts, from ketenes would be that the alkene 1< orbital can interact with both the
carbonyl and alke·ne 1< orbitals of the ketene at the same time (Figure 5.16). This would be
likely to reduce the angle dependency for the reaction.
104
o c
C""~' , c C
Figure 5.16 The overlap of orbitals in a ketene interacting with an alkene.
In the case of the dithiophosphine ylide no orbital present at 90 degrees to the reacting orbital
is present (Figure 5.17), so the effect mentioned in the above example is absent.
R-""" R--< R--J:.(
Bonding Non-bonding Anti-bonding
Figure 5.17 Molecular orbitals in a dithiophosphine ylide.
Section 5.3
Diels-Alder Reactions of Diferrocenyl Dithiadiphosphetane Disulfide.
Diels-Alder reactions of selenoketones,129 tellurocarbonyls,'30 thioaldehydes '31 .'32 have been
used to trap these reactive molecules. Thioaldehydes can be regenerated by a retro Diels
Alder reaction, enabling these adducts to be used as a storage system for the reactive
molecules. '32 In addition to acting as dieneophiles, Thioketones are also known to take part in
Diels-Alder reactions as heterodienes (Scheme 5.21).'33,'34,'35
o o H
s 0 o
Ni (R) •
62%
Scheme 5.21 Synthesis of a nine membered ring using a hetero-Diels-Alder reaction of a
heterodiene. '35 105
The reactions of dienes with the thionation reagent should be investigated. Simple 1,3-dienes
are known to react with dithiadiphosphetane disulfides.'36.,37.,38 The mechanism suggested for
the reaction is inconsistent with the generally accepted one for Diels-Alder reactions. '37
While the Diels-Alder reaction mechanism can be drawn as a free radical process, rather than
as being two electron curved arrows as shown below (Scheme 5.22), a step wise pathway
going via free radical intermediates is inconsistent with the generally accepted mechanism .
•
•
Scheme 5.22 Diels-Alder reaction of butadiene and ethylene. ,
However examples of the stepwise free radical 'Diels-Alder' reaction are known, for example
the reaction of cis-trans hexa-2,4-diene with selenoketones at 1 atm (Equation 5.9).'39
Se 0~ Me H Me H
Se + • Toluene
800 C Ar Ar Ar Ar
CFa CF3 1 atm M H Me H
59 41
Ar = meta-(CFa)C6H.
Equation 5.9.
At 12 KBar/room temperature (12000 atm) the same reaction gives a 20:80 product ratio,
suggesting a pressure enhancement of the normal Diels-Alder reaction rate, '39 as the
transition state has a smaller volume than the reactants. The cis,trans-diene is believed to
react with the selenoketone to form intermediates that may either cyclise or form the
trans,trans-diene (Scheme 5.23). As the geometry of the trans,trans diene is much better for a
Diels-Alder reaction this diene will be likely to react rapidly with the selenoketone.
106
c S • ION .)IN Slow - '1 N
1l
j
.5CN - ~ ",'"
'"
1l
.~ - ~ ",'" ",'"
1l
~ S •
~ . ",AN Fast - ",'" 'I Scheme 5.23 The reaction of a diarylselenoketone with cis-trans-hex-2,4-diene. '39
It is noteworthy that a mixture of P 4SlO and P(S)CI3 will react with alkenes and dienes as a
synthon for CIPS2• in the formation of cyclic compounds (Scheme 5.24). '40 The first of the two
reactions could have as an initial step an ene reaction followed by a ring closure.
P .S,ofP(S)CI3
(P)CI •
11 S
( P ,S1ofP(S)CI3 ICs • ~\\CI S
Scheme 5.24 The reactions of propene and butadiene with P4S,ofP(S)CI3.
107
When the reaction mixture included some PCI3 and was carried out at a lower temperature, a
more complex mixture was obtained which included the following compounds (Scheme
5.25)."0
S I 11
~s/P\~ Cl
S S 11 11
CI/~~~'CI Cl Cl
Scheme 5.25 Products from the reaction of propene. PCI3 and P(S)CI3.
Other phosphorus sulfur compounds including P .S,oIEt3N'41 (Scheme 5.26) and a
metadithiophosphonate '6 have been shown to take part in Diels-Alder reactions. Note that the
reaction of the P .S,o is a complex multistep reaction.'41
R
\..-
~R o
1-<Et3NHh 8
yyR P-8
II 8
-8
R
) R,(
•
•
1 (t) 8
Et3NH ~ 8/ ~8 e
R
(t)=i Et3NH 8
e I 8-P .f/ '8 R
R
Scheme 5.26 The reaction of P .S,o with Cl,J3-unsaturated ketones.'"
108
---------- -
The mechanism of the metadithiophosphonate with 1,3-dienes is more simple (Equation
5.10).'6
Equation 5.10
R is 2,4,6-tri-tert-butylphenyl
A group of reactions has been observed for a reactive selenium phosphorus compound with
acetone, acetonitrile and carbon disulfide (Scheme 5.27). 142,143,144 These reactions are likely to
have mechanisms that include some pericyclic steps.
PhPCI2 + Li2Se
Scheme 5.27 Formation of heterocycles from PhPCI2/Li2Se.
Thioaldehydes, with a few exceptions" .. ,146 are generally extremely reactive species that
rapidly form polymers, oligomers or undergo cycloaddition reactions, for instance
thiobenzaldehyde rapidly forms trimers (Equation 5.11) and a resin.'47
PhCHO
Ph
H2S S~S HCI ~ Ph~S~Ph
36%
Equation 5. 11
Even with the presence of two tert butyl groups ortho to the thioaldehyde, a variety of
reactions can still occur, (Scheme 5.28).'45
109
S
X i,600C
~s N1HJE,IOH OOC ~ - Ar~NN~
sa"
e '" ~ PhC=N=NPh Room lemperture Co
\
0 2 slow reaction at room temperture
""'HO
Scheme 5.28 Reactions of a hindered and stable thioaldehyde.'4s
Thioaldehydes have been used in synthetic chemistry, they have been released from Diels
Alder adducts in the presence of a trapping reagent (Scheme 5.29).'48 In principle the same
method could be used for the storage of selenoketones and selenoaldehydes.
a • Ph~S/OH + [ S~Ph ]
~j ~···-S
tsOCNH~1 ell r~J""4......COOEt o 1
S
• ~[S~COOEtl [2+4)
-}-N~
tsOCNH I S N-...(
o tOOEt Major product
Scheme 5.29 'The use of anthracene. as'pa~ of a storage system for thioaldehydes.
If the 1,3-diene was excessively reactive towards the thionation reagent then the conversion of
the carbonyl to thiocarbo~yl would be reduced. Also the reaction mixture would become more
110
complex as another product would be forming in the mixture: This portion of the study is partly
about chemical compatibility of the thionation reagent towards the dienes. A further reason for
attempting the reaction of FC2P2S, with a 1,3-diene is to provide a thiaphosphinane, which can
be compared with the thiaphosphetanes.
While LR has already been used successfully, with anthracene present in benzene to form a
thioaldehyde adduct (Equation 5.12),"9 the reaction of dithiadiphosphetane disultides with
anthracene at higher temperatures had not been investigated.
LR .. Anthracene
CsHs t>.
S H'
59 %
Equation 5. 12
For comparison with anthracene and the products from the bicyclic alkenes, the reaction of
2,3-dimethylbutadiene with Fc2P2S. was attempted. The reaction of 2,3-dimethylbutadiene
with FC2P2S. gave as expected a high yield of the Diels-Alder adduct 41 (op 69.2 ppm, u(P=S)
666 cm-1) (Scheme 5.30).'21 While the compound does have stereocentres, 41 is formed as a
racemic mixture and no attempts were made to separate the enantiomers.'2' The reaction of
anthracene with Fc2P2S. in hot xylenes was attempted, no change was observed by TLC
(Scheme 5.30). This was not entirely surprising as anthracene is an unreactive 1,3-diene
when its Diels-Alder reactivity is compared with an open chain 1,3-diene. When NpP2S. was
treated with 2,3-dimethylbutadiene, under similar conditions, almost no reaction occurred
(Scheme 5.30). The inertness of NpP2S. towards the diene is consistent with the hypothesis
that the diene reacts with the dithiophosphine ylide and not with the dithiadiphosphetane
disulfide.
No reaction
41
Scheme 5.30 Treatment of dithiadiphosphetane disulfides with dienes.
III
X-ray crystallography revealed 41 to have a pseudo boat shaped C.PS ring (Figure 5.18 and
Table 5.5).'2' The phosphorus sulfur bond lengths are not significantly different to those in 43
[2.102(2) AI and 44 [2.095(1) AI and the C-S distance is similar to that in 43 [1.850(6) AI.
C16 C15
Figure 5.18 Molecular structure of compound 41'21
Table 5.5 Selected bond lengths (A) and angles (0) found in the molecular structure of 41.'2'
S(1)-P(1) 1.944(3)
S(2)-P(1) 2.086(4)
S(2)-C(11) 1.840(9)
P(1)-C(14) 1.816(8)
P(1)-S(2)-C(11) 100.4(4)
S(1)-P(1)-S(2) 114.7(2)
S(1)-P(1)-C(1) 112.5(3)
S(1)-P(1)-C(14) 114.5(3)
S(2)-P(1 )-C(14) 101.6(3)
S(2)-P(1)-C(1) 106.5(3)
C(1 )-P(1 )-C(14) 106.0(4)
P(1)-S(2)-C(11) 100.4(4)
S(2)-C(11 )-C(12) 112.4(6)
C(12)-C(13)-C(14) 118.1(8)
The Diels-Alder reaction normally involves the frontier orbitals (HOMOs and lUMOs).
However in this case it is likely that the HOMO (non bonding orbital is not involved) of the
dithiophopshine ylide, instead it is likely that the lowest occupied 11 orbital is interacting with
the lUMO of the diene (Figure 5.19).
112
LUMO
HOMO
1.3-Dimethylbutadiene
~
l,,'/
~_11
,
,.><, 11
Dithiophosphine ylide
~ LUMO
~HOM
Figure 5.19 The 1l-orbitals on the atoms taking part in the Diels-Alder reaction.
A related compound (177) has been reported. similar to 41 but with the endocyclic sulfur
missing. was formed by the electrophilic aromatic substitution of ferrocene with a 1-bromo-2.5-
dihydro-1 H-phosphole (Equation 5.13).'50
0 FcH Q AICI3 • CS2 Equation 5. 13 Ll. I I Br Fc
177
Section 5.4 The Ring Opening Reaction of the Diels-Alder Adduct.
In the proposed mechanism for the formation of the antisludge agents for engine oils. a step in
which an 'alkyl carbon was deprotonated allowed a ring-opening step. As Diels-Alder adducts
113
of other dithiophosphine ylides were reported to undergo ring opening when treated with
sodium hydride, the anions formed were quenched with carbon electrophiles to give S-aryl
and S-alkyl dithiophosphates. '37 It was found that treatment of compound 41 with BuLi in THF
followed by the addition of benzyl bromides or 2,4-dinitrochlorobenzene gives moderate yields
of similar compounds 42, 178 and 179. The molecular structure suggests that carbon carbon
double bond a,l3- to the phosphorus has Z stereochemistry suggesting 42 was formed from a
sulfur anion where this cis arrangement exists. As the isolated yield is not 100%, it would be
unreasonable to assume that only one ring opening process is in operation, and the observed
one may be simply the most rapid one.
x Y rr ..... <--R_X_
~~'SR Fc
42 R= CH2Ph 180 R= o-MeCeH.CH2 181 R= 2,4-dinitrophenyl
1 BuLi
:(s II
~'s Fc
It was hoped that the terminal sulfur would interact with the 2,3-dimethylbut-1,3-dien-1-yl
group to give a possible homo aromatic ring. A crystal suitable for single crystal X-ray
crystallography was obtained by cooling a hot solution of 42 in EtOAc. The molecular structure
was then obtained (Figure 5.20 and Table 5.6). In this solid state structure no inter or intra
molecular attraction were observed between the terminal sulfur and the dieneyl group. The
bond between the 2 and 3 carbon atoms has rotated and the sp' carbons are not coplanar.
114
Figure 5.20 Molecular structure of compound 42.
Table 5.6 Selected bond lengths (A) and angles (0) found in the molecular structure of 42.
S(1)-P(1) 1.946(2)
S(2)-P(1) 2.108(2)
S(2)-C(11) 1.812(7)
P(1)-C(1) 1.774(6)
P(1)-C(18) 1.787(6)
P(1)-S(2)-C(11) 101.4(2)
S(1 )-P(1 )-S(2) 114.8(1)
S(1)-P(1)-C(1) 115.8(2)
S(1)-P(1)-C(18) 114.3(2)
S(2)-P(1 )-C(1) 99.6(2)
S(2)-P(1)-C(18) 101.9(2)
C(1)-P(1)-C(18) 108.8(3)
While the P=S and Cop bond lengths are not significantly different from the Diels-Alder adduct
41, the P-S bond is longer. Like 41, 42 was formed as a racemic mixture and no attempts
were made to separate the enantiomers or devise a stereoselective synthesis. Treatment of
43 or 176 with strong bases, followed by carbon containing electrophiles, gave complex
mixtures from which it proved impossible to isolate or identify any of the compounds present.
lIS
Section 5.6 Reactions of Thioaldehydes with FC2P2S4
It was anticipated that treatment of benzaldehyde with FC2P2S4 would form the highly unstable
thioaldehyde, which would undergo further transformations. C-P-S heterocycles are
accessible in high yields using LR (Scheme 5.31 ).'49.15,.'52
S An \\ /
P S/ 'S I I CsHs
FsC~S~CsF5 .... 0---:"''-''-
P~h Ph2CO • PhMe
'" 95%
+ Ph2CS 92 %
LR
'" P~h S Ph
• S MeOH84% PhMe99 %
Scheme 5.31 Formation oftrithiaphosphinanes from LR.'49.'51.152
In the first two examples it is unlikely that three molecules could react in a single step. One of
the following stepwise mechanisms is more likely (Scheme 5.32).
o
6 LR
S'" /An "'P
S 11
6 S Attack oflhe~hione as a nucleophile
1 [2+ 2J cycloaddilion (1 reaction
yY--,-s-~-An
'01 •
S A. 11 -s-P S/ 'An
6 S
16
Scheme 5.32 Possible mechanisms for the formation of trithiaphosphinanes.
116
The formation of trithiaphosphinanes can be rationalised by a series of pericyclic reactions.
The LR could thionate some of the ketone (or aldehyde) to give the thione which then
undergoes a [2+2] cycloaddition with the dithiophosphine ylide. This could give a
dithiaphosphetane which could then either undergo another [2+2] cycloaddition with a second
thione molecule, or it could ring open to give a dipole species which could react with another
molecule of the thione.
The reaction of benzaldehyde with Fc,P,S. was postulated to give a 1,3,5-
trithiaphosphorinane ring, while pentafluorobenzaldehyde is known to react with both LR and
anthracene. As expected when Fc,P,S. was reacted with benzaldehyde, the
trithiaphosphorinane (45) (op 72.0 pp m) was obtained in low yield (reaction conditions were
not optimised) (Scheme 5.33). This reaction was performed with trimethylacetaldehyde giving
a similar product (46) (op 72.3 ppm).
o S
©Y -FcPOS cgI'
Scheme 5.33 Formation of 45 from Fc,P,S •.
This yield of 45 of 8% is based on the phosphorus starting material, though in the reaction
mixture at least 16% of the thiobenzaldehyde was consumed by this side reaction. If the
reaction had been used to make thiobenzaldehyde in situ then a reduction in the effective yield
of the thioaldehyde could be expected. One mild method for forming trithiobenzaldehyde is to
use hydrogen sulfide and a mineral acid, this could be modified to give the Diels-Alder
adduct.'47 The addition of alkyl groups to the anthracene would be likely to improve the
reaction by increasing the solubility of the anthracene.
The X-Ray structure of 45 was obtained (Figures 5.21 and 5.22 and Table 5.7). The C2PS3
ring in this structure is chair shaped and the phenyl groups are both equatorial.
117
Figure 5.21 Molecular structure of compound 45.
The C,PS3 ring that is common to both 45 and 46 is shown below with the phenyl and
ferrocenyl groups omitted for clarity.
C7
81 Figure 5.22 The trithiaphosphinane ring of 45.
118
Table 5.7 5elected bond lengths (A) and angles (D) found in the molecular structures of 45 and
46.
Property 45 46
S(1)-P(1) 1.937(2) 1.9384(14)
S(2)-P(1 ) 2.102(2) 2.0906(13)
S(6)-P(1) 2.086(2) 2.0811(14)
S(2)-C(3) 1.841(4) 1.856(4)
S(4)-C(3) 1.815(5) 1.820(4)
S(4)-C(5) 1.795(5) 1.812(4)
S(6)-C(5) 1.847(5) 1.852(4)
P(1)-C(19) 1.764(5) 1.779(4)
P(1 )-5(2)-C(3) 97.8(2) 98.27(12)
C(3)-5(4)-C(5) 105.1(2) 101.1 (2)
P(1 )-5(6)-C(5) 98.0(2) 99.40(12)
S(1 )-P( 1 )-5(2) 112.58(8) 114.52(7)
S(1 )-P( 1 )-5(6) 115.25(9) 115.32(6)
S(1 )-P(1 )-C(19) 115.9(2) 115.34(13)
S(2)-P( 1 )-S(6) 103.84(7) 104.80(6)
S(2)-P( 1 )-C( 19) 104.6(2) 103.08(12)
S(6)-P( 1 )-C( 19) 103.3(2) 102.17(13)
S(2)-C(3)-S(4) 113.9(3) 111.7(2)
S(2)-C(3)-C(7) 110.1(3) 110.1(3)
S(4)-C(3)-C(7) 106.0(3) 111.1(3)
S( 4 )-C(5)-S(6) 116.4(3) 112.8(2)
S(4)-C(5)-C(13) 107.7(3) 112.2(3)
S(6)-C(5)-C(13) 105.9(3) 108.0(3)
The P-S bond lengths in 46 are significantly shorter than the corresponding bond in 42, 43, 44
and FC2P2S" while the lengths in the phenyl compound are significantly shorter than the mean
P-S bond length in Fc2P2S •.
In both trithiaphosphinanes, whilst the heterocyclic rings are almost symmetric about a mirror
plane passing through the phosphorus and 5(4), differences between the two sides of the
rings are present. Other than the 5(2)-P(1) distance within the trithiaphosphinane ring no
significant differences in bond length exist between the phenyl and telt-butyl compounds. In
both structures the endocyclic P-S bonds are slightly different in length, but so far no
satisfactory explanation has been devised. In the telt-butyl compound the angles within the
119
--,-
ring at C3, S4 and C5 are smaller than those angles in the phenyl compound (Figure 5.23).
The bulky ten-butyl groups are being pushed.away from S4, which then affects the shape of
the ring.
s:~~ I . Smaller Smaller I 6 Larger
C~~ler C, C/ Larger3 ~/ Large~ "C
4
Figure 5.23 Schematic showing changes in angles in the trithiaphosphinane ring on going
from 45 to 46.
Examination of the crude product mixtures by 31p-{'H} NMR spectroscopy, shows that no
other isomer is present in any large amount. If the formation of this compound is reversible
then given time the most thermodynamically stable isomer would be obtained. The
arrangement of the ferrocenyl group is such that it is at the greatest distance from the phenyl
groups and the hydrogens. This could be the reason for the formation of the compound where
the phenyl groups are both equatorial arranged on a chair shaped P-S-C-S-C-S- ring.
Structures 1,2,3, and 4 can be interconverted by bond rotation (Scheme 5.34). In structures 1
and 2 the phenyl groups are well separated from each other and the hydrogens on the
trithiaphosphorinane ring. In structures 3 and 4 the phenyl groups are closer to each other
(Scheme 5.34).
H S
1~ 11 H P Ph ! lSj --Fc
SI -S
2.
Ph
4.
S S 11
Ph~Ph ./P __ -S./ / Fc
S
S
S u 1l'1---FO
Ph Ph
Scheme 5.34 Possible arrangements of the C3PS3 ring in 45 with the phenyl groups arranged cis to each other.
120
After investigating the reaction of thioaldehydes with Fc,P,S. when the thione is generated
rapidly, an attempt to react Fc,P,S. with thiobenzaldehyde where the thioaldehyde is slowly
formed in situ was made. In terms of HSAB theory nitrogen is 'softer' than oxygen, so "the
reaction of an imine was chosen as a means for slowly forming thiobenzaldehyde at an
elevated temperature. Fc,P,S. and PhCH,N=CHPh (153) were heated together (45 h) in a
mixture of toluene and xylenes.
After repeated chromatography and recrystallization a small yield of a product (152) (op 86.3
ppm) was obtained whose 'H NMR spectrum had a complex aromatic area, and a doublet (OH
5.21 ppm 14 Hz) outside the ferrocenyl region was obtained. (Figure 5.24).
--' '-::::-:-1...... L/ Lo... i J j I'
7.00 6.00 5.00 Figure 5.24. 'H NMR Spectrum of 152.
In the 13C NMR spectrum of 152 only one carbon environment, other than those due to phenyl
and ferrocenyl groups, was present indicating that the product could not be a
thiazaphosphetane, as this would have two 13C NMR signals out of the ferrocenyl and
aromatic regions (Equation 5.14).
IT jPh Fc-P-N
~-tPh SxPh
S"'" / . .p Fc .. •• 's Ph
Equation 5.14
121
Considering the 'H and 13C NMR spectroscopic data and the molecular ion at 492 amu
(,'C,.'H'356Fe31p3'S3), the structure (152) containing a dithiophospholane ring was assigned
(Equation 5.15). If the phenyl groups of 152 are arranged cis to each other, one of the phenyls
could be equatorial while the other would be axial making the two potentially inequivalent by
NMR spectroscopy, depending on the rate of change from one conformation to the other.
SxPh S, /
,.P Fe"" ,
S Ph
152 Equation 5.15
To study 152 further its cyclic voltammogram was recorded (Figure 5.25); the shape of the CV
curve being reasonable for a compound with a single ferrocenyl group present.
~~o.o
1.3 E(VoltsP.O 0.8 0.6 0.4 0.2 0.0
Figure 5.25 The cyclic voltammogram for 152.
To confirm the identity of 152 a crystal was grown and a single crystal diffraction study
indicates the compound to be a C,PS, heterocycle (Figure 5.26 and Table 5.8).
122
Figure 5.26 Molecular structure of compound 152.
Table 5.8 Selected bond lengths (A) and angles(o) found in the molecular structure of 152.
S(1 )-P(1) 2.095(2)
S(2)-P(1) 2.089(2)
S(3)-P(1) 1.938(2)
S(1)-C(1) 1.836(4)
S(2)-C(2) 1.832(4)
C(1 )-C(2) 1.540(5)
P(1)-C(15) 1.778(4)
P(1)-S(1)-C(1) 101.0(1)
P(1 )-S(2)-C(2) 97.3(1)
S(1 )-P(1 )-S(2) 99.20(6)
S(1)-P(1)-S(3) 118.18(7)
S(2)-P(1 )-S(3) 112.20(7)
S(3)-P(1)-C(15) 112.7(1)
S(1 )-P(1 )-C(15) 103.9(1)
S(2)-P(1)-C(15) 109.6(1)
S(1 )-C(1 )-C(2) 108.6(2)
S(2)-C(2)-C(1) 111.7(3)
The mean P-S and C-S bond lengths in 152 are not significantly different to the mean bond
lengths in the trithiaphosphinanes 45 and 46. The mean S-P-S(3) angle of 115.19(7t is larger
than the corresponding angle in the diphenyl trithiaphosphinane (45) but it is not significantly
different to the mean angle in the di-tert-butyl trithiaphosphinane (46). While the P-S bond
lengths of 152 are similar to that found for two thiadiphospholanes with tri- (167) and tetra
(180) co-ordinate phosphorus 125.153 (respectively 2.087(2) A and 2.09 A), the P-S bond lengths
in 152 are shorter than those found in two thiadiphospholanes (181) and (182) with penta co
ordinate phosphorus atoms (mean P-S lengths of 2.134 and 2.142 A) (Scheme 5.35).'54.'55
123
181
S S ''pt] / ,
Ph S
180
Ph
CI"QCS 1
0
O '-p/ / ,
S 0
182
Scheme 5.35 Dithiaphospholanes.
Cl
Cl
Cl
Cl
The most likely source of the phenyl groups found in 152 was the thiobenzaldehyde assumed
to be the sulfur containing side product from the formation of the nitrogen phosphorus
compounds (Scheme 5.36). The formation of this heterocycle did pose a mechanistic
challenge. as a C-C bond is formed and 152 cannot be rationalised as being an adduct of
thiobenzaldehyde and the dithiophosphine ylide. One suggestion as to the mechanism would
be the [2+2] cycloaddition of thiobenzaldehyde with the dithiophosphine ylide followed by a
second [2+2] cycloaddition. After the second cycloaddition an atom of sulfur is eliminated from
the molecule to give 152. The formation of the compound between the dithiophosphine ylide
and the thiobenzaldehyde. suggests that in any synthesis of an adduct of thioaldehyde using a
dithiadiphosphetane disulfide then an excess of the thionation reagent must not be added to
make the reaction more rapid.
S II
Fe-P \\
S
5 11 /'---..
Fe-P-N Ph S
~-\Ph II ___ , Fe-P-~
_ ~ \'s---.C~y /p~ ,..,Bn Ph
Fe N
1 [2+2]
S, /SXPh .. .,p .. ~---
Fe"" '5 Ph -5
5 \\~5 Ph
Fe r-j.. .. .. !-------. 5 ..
....... 5 Ph
Scheme 5.36 Possible mechanism for the formation of 152 from Fc,P,S •.
124
A precedent for the final step (loss of a sulfur atom) can be taken from the reaction of dimethyl
dithiadiphopshetane disulfide with trimethylsilyl azide (Scheme 5.37).'56
-S 1/
II __ ---N-Si Me-P--..::3 II ----.. \
''s- IIN@ ...... ---·N
U
S \I P-Me
QII" S('. '. N-SiMe3 ''/1
Me-P \\ S
Scheme 5_37 Reaction of dimethyl dithiadiphosphetane disulfide and trimethylsilyl azide.
The reasons for the apparent different outcome could include the formation of a complex
mixture from which only some of the products can be isolated. In addition to the problem of
the thiocarbonyl reacting with itself, the possibility of the thionation reagent reacting with a
thiocarbonyl compound needs to be considered. LR is well known as being suitable for
synthesising relatively stable thiocarbonyl compounds, while with unhindered ketones and
chalcones (Benzalacetophenones) LR forms complex products which could be created by the
reaction of a thiocarbonyl compound and the thionation reagent.
In addition another product (op 65.1 ppm) was isolated, from Fc2P,S. and 153, which was
thought could have been the thiazaphosphetane sulfide. In it's 'H NMR spectrum the aromatic
region suggested that only one phenyl group environment was present, other than the phenyl
and ferrocenyl groups, the only feature present was a poorly resolved mulitplet (OH 4.16 ppm).
From NMR spectral data and as a molecular ion was found at 633 amu in the FAB MS, a
thiazadiphoshetane disulfide structure (183) was assigned (Figure 5.27).
Fc S S , / ,11 P P
II 'N/ , S l Fc
Ph 183
Fig u re 5_27 2, 4-diferrocenyl-3-Benzyl-1, 3, 2.4-Thiazadiphosphetane-2, 4-disulfide.
125
The benzyl CH2 protons (OH 4.16 ppm) were expected to be a 1:2:1 triplet in the 'H NMR
spectrum, but a more complex system consisting of a sharp single peak with a doublet on
either side was observed. A 'H/13C correlation confirmed that this complex peak was due to
the benzylic protons. By reducing the temperature the multiplet due to the benzylic protons
was seen to broaden when compared with the rest of the spectrum. This indicates that a slow
rotation is occurring about the nitrogen carbon bond. This rotation could not be frozen out at
233 K (Scheme 5.38), nor was any change to this peak observed on heating to 363 K (90°C in
D.-toluene). It is likely that the two benzylic protons are experiencing through-space effects
because they are at different distances from the ferrocenyl groups and the sulfur atoms.
Scheme 5.39 shows some different conformations that the molecule can adopt. The view is
along the C-N bond, and in structures 1 to 12 the rotation of the benzyl group is occurring.
233 K
273 K
J I I I I I I
5.111 4.5 4.111 5.111 4.5 4.0 PPM PPM
Scheme 5.38 'H NMR spectra of 185 at two different temperatures.
126
1. 2.
S Ph Fc S Ph Fc \\ I / \\ ( /
P P P-Hb P
FI Hb7 "'Ha \\
FI \\
S Ha S
3. 4.
S Fc S Hb Fc \\ Hb:::::"L::Ph / \'p~Ph-p/ P P
FI I \\ I \\ Ha S Fc Ha S
5. 6.
S Hb Fc S Hb Fc \\ I / \\ ( /
P P P-Ha P
FI Ha7 "'Ph \\
FI \\
S Ph S
7. 8.
S Fc S Ha Fc \\ Ha:::::"L::Hb / \\ ) /
P P P Hb-P
FI I \\ FI
\\ Ph S Ph S
9 .. 10. S Ha Fc S Ha Fc \\ I / \\ ( /
P P P-Ph P
FI Ph7 "'Hb \\
FI \\
S Hb S
11. 12. S Fc S Ph Fc \\ Ph:::::"L::Ha / \\ ) /
P P P Ha-P
FI I \\ FI
\\ Hb S Hb S
S Fc.. /" ....... Fc
"'P P S ..... "N/ ""'S
Ph) i View along this arrow
Scheme 5.39 Different arrangements of the benzyl group
possible through rotation about the C-N bond.
Because of slow rotation about the P-C bonds, four different proton environments and five
carbon environments are seen in the NMR spectra for the substituted Cp ring. In the 13C-{'H}
NMR spectrum the quaternary carbon of the ferrocenyl group cannot be found. As four
127
environments can be seen clearly, in the 'HI'3C correlation the different peaks are not due to
coupling to the phosphorus atom (Figure 5.28).
80
70 -E a. a. -~ ..c (/)
60 co
.!::! E Q)
..c (,)
50 c o .0 ..... co o
.. I~
.-
I I I
6.0 5.0 4.0 Proton chemical shift (ppm)
Figure 5.28 13C_'H Correlation for 183.
Interestingly P-ferrocenyl P-N-C-S-C-N-, P-S-C-C-S- and P-S-C-S-C-S- rings have two sharp
cyclopentadieneyl carbon environments for the substituted Cp ring suggesting either more
rapid rotation about the C-P bond or that the chemical shifts for the molecule in the two
extremes of conformation are closer. The presence of four instead of two proton
128
environments for the substituted Cp ring is an indicator of a molecule where the groups on the
phosphorus are not arranged symmetrically about the plane passing through the quaternary
carbon and iron atoms (Figure 5.29). The P-ferrocenyl P-O-C-C-O- ring compounds do have
more than the expected two environments, suggesting a molecular geometry in solution
similar to that found in the crystal structure. The aromatic region of the 'H and 13C-{'H} spectra
for 148 shows such effects very clearly while the effect is less noticeable in the ferrocenyl
region.
f~----
l .... ~ .... Figure 5_29 Ferrocene with a plane passing through the iron and a carbon in one ring.
Those compounds that contained ferrocenyl groups were examined by cyclic voltammetry,
and it was found that all the compounds other than 44 had reversible redox couples.
129
Section 5.7 Experimental
Reaction of FC2P2S, and bicyclo[2,2, 1]hepta-2,5-diene (162)
Into a thick walled glass tube was placed Fc,P,S. (3.1 g. 5.5 mmol) and 162 (5 ml. 4.3g. 46
mmol). The reaction mixture was cooled to -196 ·C before all air was removed. The tube was
sealed and allowed to warm to room temperature before being heated at ca. 80·C (16 hours)
with stirring. The red brown reaction mixture was allowed to cool to room temperature before
the excess 162 was removed using a high vacuum line to yield a brown tar that solidified to
give 43 as a yellow solid (2.82g. 7.6 mmol. 69% isolated). 43 was found to be insoluble in
ether, but to be soluble in chloroform and dichloromethane. 43 may be recrystallized from
ethyl acetate. m.p. 120-121.5·C. (Found. C, 54.6; H, 4.4. C17H17FePS, requires C, 54.8; H,
4.6%). IR 3126w, 3106w, 3094w, 3068m, 3061m, 3000m, 29825, 29695, 29565, 2882w,
1787w, 1551w, 1542w, 1459m, 1409m, 1390m, 1365m, 1350w, 13195, 1279m, 1256m,
1222w, 11785, 11705, 1149m, 1107m, 1064w, 1056w, 1034m, 10195, 10075, 976m, 939m,
926m, 911w, 897w, 862m, 8295, 8185, 7855, 7665, 7535, 7135, 686m, 631vs, 535m, 4905,
2765, 444m, 400w, 365w, 348m, and 326m (cm-'). op (COCI3 ) 64 ppm. Oc (COCI3) (ppm) 136.5
[d J(PC) 15 Hz], 135.9,73.5 [d J(PC) 16 Hz], 72.4 (m), 70.0, 57.3 [d J(PC) 53 Hz], 47.2, 43.3,
42.7 and 36.4 [d J(PC) 7 Hz]. oH (COCI3) (ppm) 6.3 (2H, m), 4.7 (2H, m), 4.6 (2H, m), 4.2 (4H,
5), 3.0 (5H, m), and 1.6 [1 H, d 'J('H-'H)=9.8 Hz]. On irradiation of the doublet at 1.6 ppm, part
of the complex peak at 3.0 ppm changed from a doublet to a singlet. 'H (COCI3) COSY o(ppm)
6.15 [3.27], 6.10 [3.06], 4.74 [4.54], 3.26 [2.97], 3.26 [1.70], 3.13 [1.70], 3.08 [1.70], and 2.97
[1.70]. 'H/'3C (COCI3) Correlation 'H o(ppm) [13C o(ppm)] 6.2 [136.5], 6.1 [135.9],4.7 [73.5],
4.7 [72.4], 4.5 [72.4], 4.2 [70.0], 3.1 [57.3], 3.1 [47.2], 3.3 [43.3], 3.0 [42.7], 1.6 [42.7] and 3.1
[36.4]. OH (Toluene-O.) (ppm) 5.68 (m), 4.07(m), 4.61 (m), 4.22 (m), 4.17 (5), 3.15 (d, 9.7 Hz),
3.07 (m), 2.6 (m), and 1.5 (d, 9.7 Hz). On heating to 90·C(363K) no change was observed in
the spectrum. On irradiation of peak at 1.50 ppm the doublet at 3.15 becomes a singlet. 'H
COSY (Toluene-O.) o(ppm) 5.68 [3.07], 5.68 [2.59], 4.70 [4.16], 4.62 [4.21], 3.15 [2.59], 3.15
[1.50], 3.07 [2.59], and 2.59 [1.50]. Oc (Toluene-O.) (0 range 100-0 ppm) (ppm) 74.4 [d,
J(PC)15.7 Hz], 72.8 [d J(PC) 14.5 Hz], 72.4 [d J(PC) 11.3 Hz], 70.4, 57.8 [d J(PC) 53 Hz],
47.6 [d J(PC) 2 Hz], 43.8 [d J(PC) 3 Hz], 43.1, and 36.4 [d J(PC) 7.4 Hz]. MS(EI+) rnlz 372
(M+), 280 (FcPS,), 248, 217, 184, 1.55, 121,91,69,51, and 31. CV. 0.70 Volt and reversible.
Room temperature reaction of 12 and 162.
12 (22 mg. 36 flmol) was dissolved in COCI3 and a drop of 162 was added to the NMR tube.
After 4.5 hours the signal due to 12 at 18 ppm was replaced by a peak at 64.1 ppm. The
reaction mixture was evaporated down to a red tar (31 mg) which even after drying in high
vacuum overnight retained some 162. IR (thin film) 3064m, 29745, 1567w, 1543m, 1474m,
14555, 13875, 1312m, 1282m, 12515, 1229m, 1184m, 1148w, 10965, 10395, 980m, 940m,
130
895w, 868s, 832s, 789m, 765m, 754m, 730s, 703s, 658m, 631s, 540w, 523w, 490s, and 444w
(cm-'). op (ppm) 64.1. OH (pp m), 6.1 (2 H, m), 4.6 to 4.0 (9 H, m), 3.4 to 2.8 (4 H, m), and 2.0 (8
H, complex). MS(EI+) mlz molecular ion found at 400.0174 ['2C'9'H2,56Fe"p32S2 requires
400.01713 (error of 0.6 ppm)].
The attempted reaction of FC2P2S, and cyc/ohexene.
FC2P2S, (1.88g. 3.4 mmol) and cyclohexene (3.6 ml. 2.9g. 35 mmol) were heated together
overnight at 78°C. The reaction was allowed to cool before being opened and being filtered.
The red solid obtained, was washed with toluene before being dried to give FC2P2S. (1.52g.
81% recovery). The identity of FC2P2S. was confirmed by infra red spectroscopy.
Reaction of norbornene (175) and FC2P2S,.
FC2P2S, (1.1g. 2.0 mmol), 175 (4.1g. 44 mmol) and toluene (8 ml) were heated together in a
sealed tube at ca 80°C for 63 hours before being allowed to cool. After removal of the volatile
organics in high vacuum a red oil remained (2.26 g), which was subject to purification by flash
column chromatography on silica (eluting with petrol before 20% CH2CI2 in petrol) to give a red
oil which crystallised on storage in a freezer (1.58g). Then recrystallization from ethyl acetate
(5 ml) followed by drying in high vacuum gave 176 as an orange crystalline solid (431 mg. 1.2
mmol. 29 %). m.p. 101-112°C. (Found: C, 54.2; H, 4.9; N, 0.1. C17H'9FePS2 requires C, 54.5;
H, 5.1; N, 0.0%). IR 3079m, 29515, 2866s, 1474w, 1410m, 1388w, 1364w, 1347w, 1308m,
1295m, 1249m, 1213w, 1198m, 1188m, 1179s, 1170s, 1138m, 1111w, 1104m, 1055w,
1048w, 1034m, 1018s, 1005m, 963w, 940w, 920w, 892w, 865w, 842s, 823s, 8065, 779s,
752m, 730s, 680w, 6485, 621s, 600m, 530s, 4955, 482s, 456s, 376m, and 324w (cm-'). op
66.4 ppm. Oc (ppm) 73.5 [d J(PC) 15 Hz], 72.4 (m), 70.0, 63.2 [d J(PC) 57 Hz], 43.0 [d J(PC)
12 Hz], 41.6 [d J(PC) 2.5 Hz], 38.3 [d J(PC) 3.4 Hz], 34.1, 28.4 and 28.1 (m). OH (ppm) 4.7
(m), 4.5 (m), 4.2 (s). Overall integration for the ferrocenyl region is 13 H. 3.45 (m), 3.29 (m)
combined integration of these two peaks is 3.86H, 2.99 (2H, m), 2.63 (1.6H, m), 2.31 (d), 1.99
(Impurity), 1.6 (m) and 1.1 (m). Total integration for the region 2.4-0.9 17.8H. 'H-'H COSY
o(ppm) 3.5 [3.3], 3.5 [1.5], 3.3 [1.5],3.0 [2.6], 3.0 [1.5],3.0 [1.2],3.0 [1.0],2.6 [1.6],2.3 [1.7],
2.3 [1.5], and 1.6 [1.1] Cross peaks due to the ferrocenyl group have been ignored here. 'H
NOESY 3.4 [3.3], 3.4 [3.0]w, 3.4 [1.5]w, 3.3 [1.5]w, 3.0 [2.25]w, 3.0 [1.5], 2.6 [1.6]w, 2.3 [1. 7]w,
2.3 [1.5]w, and 1.7 [1.1]w. 13Ci'H Correlation 'Ho(ppm) ["C o(ppm)], 4.73 [73.4], 4.79 [72.5],
4.53 [72.3], 4.29 [70.0], 3.38 [63.2], 3.52 [43.0], 2.34 [41.6], 2.70 [38.3], 3.06 [34.1], 1.55
[34.1], 1.66 [28.4], 1.12 [28.4], 1.66 [28.1], and 1.12 [28.1]. Oc (ppm) 73.5 d(15 Hz), 72.4 m,
70.0,63.2 d(57 Hz), 43.0 d(12 Hz), 41.6 d(2.5 Hz), 38.3 d(3.4 Hz), 34.1,28.4 and 28.1
multiplets. OH (dB Toluene) 4.73 (1H, m), 4.66 (1H, m), 4.24 (m), 4.17 (m), 4.17 (5). Total
integration for peaks at 4.24 and 4.17 ppm is 7H, 3.24 (1H d, 10.6 Hz), 3.0 to 2.8 (2H, m), 2.55
(1H, d, 10.9 Hz), 1.94 (1H, br s), 1.4 to 1.1 (3H, m), and 0.8 to 0.6 (2 H, m). MS(EI+) mlz 374
131
M+, 280 (M-C7H,o)+, 217 (FcS)+, 184, 155, 121,84,66,47, and 31. CV, reversible redox
couple at 0.67 Volt relative to a SCE.
The reaction LR and 162.
The reaction of LR (1.86 g. 4.6 mmol) with an excess of 162 (5 ml. 4.2 g. 46 mmol) was
carried out in the same manner as above to give a white solid (0.88 g), after removal of
solvent and recrystallization from ethyl acetate. This solid when examined by 'H NMR
spectroscopy was found to be contaminated with ethyl acetate. The product was dissolved in
CH,CI, (3 ml) and to this was added ether (4 ml) followed by trituration gave 173 as a white
solid (0.364g. 1.2 mmol. 13 %). After re-examination with 'H NMR spectroscopy the
compound was now found to be free of ethyl acetate. m.p. 161-162°C. Found: C, 57.0; H, 5.1;
N, 0.0. C'4H'50PS, requires C, 57.2; H, 5.1; N, 0.0%). IR 3055w, 29855, 2836m, 15895,
1564m, 1495m, 1479w, 1463m, 1450w, 1439m, 1406m, 1320m, 1308m, 12925, 1276m,
12595, 1221w, 11805, 1146m, 11005, 10235, 989w, 976w, 928m, 906w, 895w, 865w, 8355,
816m, 800m, 7875, 7665, 7505, 7025, 688m, 6545, 628m, 6145, 5305, 519m, 507m, 464m,
414m, 341m (cm-'). Bp (ppm) 62.55. Bc (ppm), 136.5 [d J(PC) 15 Hz], 135.8 [d J(PC) 1.8 Hz],
133.4 Id, J(PC)14 Hz], 113.9 [d J(PC) 14 Hzl, 57.0, 56.1, 56.4, 47.4, 43.8, 42.8 (CH,), and
36.8 [d J(PC) 8 Hzl. BH (ppm), 8.1 {2H, ddrJ(31 p-'H)=14 Hz, 3J('H-'H)=8.8 Hz]}, 7.0 (2 H, m),
6. (2 H, m), 3.9 (4 H, 5), 3.3-3.0 (6H, m), 1.7 (2 H, d) MS(EI+) mJz 294 (M+), 228, 202 (M
H,S,)+, 202 (M-C7H.)+, 165, 139, 91, 66 (H,S,), 39.
It was found that by heating LR with 162 (20 equivalents) under reflux (90 minutes) before
evaporation also forms the same product.
The reaction of bis(4-butoxy-3-'Butylphenyl) dithiadiphosphetane disu/fide (14) with
norbomadiene (162).
14 (1.13 g. 1.88 mmol) and 162 (4.1 ml. 3.5 g. 37.6 mmol) were reacted in the same manner
as above. After being allowed to cool, the solvent was removed in vacuum forming a
gelatinous solid. This was dissolved in ether (4 ml) and after removal of the ether a waxy solid
was obtained. A sample was withdrawn for spectroscopy (71 mg). IR 3124w, 2062m, 29625,
1587s, 1563m, 1543w, 14555 (cluster of lines), 13945 (pair of lines), 1360s, 13215, 1202s,
11865, 1149s, 10915, 1067m, 10235, 10065, 976m, 636s, 6105, 7895, 7665, 7295, 7035,
687m, 662m, 6245, 596m, 583m, 5105, 4755, 4265 (cm-'). Bp, 73.9 ppm. Bc (ppm), 161.8
(quat), 144.1 (impurity), 138_8 Id J(PC) 3 Hz, quat], 137.3 Id J(PC) 15 Hzl, 136.6, 131.9 Id
J(PC) 14 Hzl, 130.9 Id J(PC) 14 Hz], 127.6 Id J(PC) 77 Hz, quat], 112.1 Id J(PC) 15 Hzl, 76.0
(impurity), 68.6 (CH,), 57_6, 57.1, 50.9 (impurity), 48.0 Id J(PC) 32 Hzl, 44.2 Id J(PC) 2.4 Hzl,
43.5 [d J(PC) 21 Hz, CH,], 37.5 Id J(PC) 8 Hzl, 35.9 (quat), 32.0 (CH,), 30.2, 20.2 (CH,), 14.5.
132
The product was washed with petrol. After the removal of the petrol extract, the gummy
residue was then allowed to stand in high vacuum to give 174 as a white solid (0.352g. 897
Ilmol. 24 %). m.p. 66-71°C. OH (ppm), 8.1 {dd ['J('H-'H)=2.3 Hz, 3J(3'p_'H)=15.0 Hz]}, 7.9 ddd
['J('H-'H)=2.3 Hz, 3J("P-'H)=13.4 Hz, 3J('H-'H)=8.5 HzJ, 6.9 {dd [3J('H-'H)=8.5 Hz, 4J('H_
31 p)=3.4 Hz]}, 6.0 (m), 4.0 (t, 6.4 Hz), 3.2 (m), 3.0 (m), 1.8 (m), 1.6 (d, 9.6 Hz), 1.5 (m), 1.3 (s),
0.9 (t, 7.4 Hz), 0.8 (m)'H COSY 01 ppm (02 ppm) 8.1 (6.9), 6.0 (3.2), 6.0 (3.0), 4.0 (1.8), 3.2
(3.0),3.0 (1.6),1.8 (1.5), and 1.5 (0.9). MS(EI) rnlz 392,326,300,262,229,207,151, 124,
91, 66, 57, and 41. Molecular ion found at 392.1400 AMU [,2C2,'H2.'·032S,"p Requires
392.1397 AMU (0.6 ppm error)J.
Synthesis of P-ferrocenyf 1 ,2 ,5 ,6,7,8-hexamethyltricyclo/3,2,"·20j-3-thia-4-phospho-o ct-7-ene-
4-sulfide (44).
A mixture of 1 ,2,3,4,5,6-hexamethylbicyclo-[2,2,OJ-hexa-2,5-diene (hexamethyl dewar
benzene) (177) (1.2 ml. 19. 6.2 mmol), FC2P2S4 (1 g. 3.6 mmol), and toluene (5 ml) was
heated in an oil bath at 70-80oC overnight before being allowed to cool. The reaction mixture
was filtered through an AI20 3 pad, CH2CI2 (20 ml) was used to rinse the AI20 3 and this extract
was combined with the filtrate. Removal of the solvents from the combined filtrates gave an
orange oil (3g). Chromatography on silica (30 g) [Elution with the following solvent mixtures in
petrol 10% toluene (200 ml), 20% toluene (200 ml), 25% toluene (200 ml) and 20% EtOAc
(200 ml)J gave an orange fraction. Removal of solvents from this fraction gave a red tar
(0.741g). Recrystallization from ethyl acetate (ca 7 ml) gave 44 as an orange solid (166 mg.
376 mmol. 5 %). (Found: C, 59.7; H, 6.1; N, 0.0; S, 14.1. C22H27FePS2 requires C, 59.8; H,
6.1; N, 0.0; S, 14.5 %). IR 3095m, 2909s, 2855s, 1655w, 1444m, 1408w, 1387m, 1374m,
1307w, 1283w, 1185w, 1167s, 1106m, 1066m, 1026s, 1000m, 903w, 838m, 814s, 759w,
720s, 699s, 650m, 626m, 536s, 508s, 485m, 456s, 421w, 396w, 349m (cm"). op, 68.4 ppm. OH
(ppm) 4.74 (1H, m), 4.64 (1H, m), 4.54 (1H, m), 4.49 (1H, m), 4.33 (5 H, s), 1.73 (3 H, s), 1.58
(s) and 1.16 (s) total of (6 H), 1.44 (3 H, s), 1.35 (3 H, s), 0.97 [3H, d J(PH) 24 HzJ. Oc
(ppm),146.4, 140.1, 81 [d 'J("P-13C)=75 HzJ, 76.0 [d 2J (31 p_13C)=15 HzJ, 72.4 [d 3J("p_
13C)=11 HzJ, 72 (m), 70.2,65 [d 'J(3'P_13C)=50 HzJ, 57.2 (m), 56.4 (m), 55.0 (m), 20.8 (m),
16.3,12.3 [d J(PC) 7 HzJ, 11.7, 11.2 and 10.7. 'H/13C Correlation.'H o(ppm) ['3C peak o(ppm)]
4.74 [76J, 4.64 [72J, 4.54 [72.4], 4.49 [72J, 4.33 [70.2J, 1.73 [12.3J, 1.58 [10.7J, 1.16 [11.2J, 1.44
[20.8J, 1.35 [11.7J and 0.97 [16.3J. m.p. 154-157°C. MS(EI+) rnlz 442,280,248,186,162,147,
121, and 91. Molecular ion found at 442.0641 amu ('2C2,'H2i'p32S2 requires 442.0641 amu,
within 0.0 ppm). MS(FAB+) rnlz 442, 280, 248, 217, and 163. The predicted isotropic
distribution was observed for the molecular ion. CV, almost reversible couple showing slow
electron transfer. With a scan rate of 200 mV s·, the redox couple is 0.65 volt.
133
Reaction of FC2P2S, and 2,3-dimethylbutadiene.
FC2P2S, (0.925 g. 1.65 mmol) and 2,3-dimethylbutadiene (3.7 ml. 2.7 g. 33 mmol) were
heated together overnight at 87-90oC. After being allowed to cool the tube contained an
orange solid mixed with excess diene. The excess diene was removed in vacuum and then
the solid 41 (1.03 g. 2.8 mmol. 86%) was scraped out of the tube. By the slow cooling of a hot
solution in ethyl acetate, a crystal suitable for a single crystal X-ray diffraction study was
obtained. Mp 141-143°C to an orange oil that decomposes above 188°C to a black tar. (Found
C 52.7%, H 5.1%, N 0.2%, CI.H ,9FePS2 requires C 53.0%, H 5.3%, N 0.0%). IR 3077m,
28875, 2857s, 1656m, 1439m, 1407w, 1399w, 1384m, 1363w, 1306w, 1292m, 1262w,
1221m, 1186m, 1167s, 1115w, 1104m, 1058m, 1024s, 1000m, 926w, 890w, 863w, 849w,
8315, 820s, 741m, 718m, 680s, 666s, 620m, 583m, 527m, 499s, 481s, 431s, 395m, 368w,
332m, 310w (cm·'). lip 69.2 ppm. lie (pp m) 130.6,127.4,73.6,72.5,72.2,71.7,70.0,46.7 (d,
46 Hz, CH2), 34.9 (CH2) , 21.0 and 19.2. IiH (ppm), 4.63 (lH, m), 4.37 (2H, m), 4.28 (5H, s)
4.17 (lH, m), 3.57 (lH, m), 3.12 [lH, dd, 2J ('H_31 p)=21.5 Hz 2J('H-' H)=14.1 Hzj, 2.82 (2H, m),
1.82 [4H, d, 'J(31 p_' H)=5.4 Hzj, and 1.56 (5H, s). MS(EI) m/z 362(M+), 280(FcPS2),
248(FcPS), 217(FcS), 184, 155, 121, 82(C.HIO), 67, 51, and 39. Redox couple is 0.66 Volt,
and reversible.
The attempted reaction of anthracene with FC2P2S, .
Anthracene (0.6 g) and FC2P2S. (0.9 g) were refluxed together in xylenes (27 ml), TLC
analysis after 1 and 2 hours indicated that no reaction had occurred.
The ring opening of 41 with BuLi followed by alkylation with benzyl bromide to give (42) p
ferrocenyl P-benzy/ sulfide P-2,3-dimethylbut-1,3.<fien-1-y/ phosphine sulfide.
To 41 (1.04 g. 2.87 mmol) was added THF (40 ml). The resulting solution was deoxygenated
by bubbling nitrogen gas through it. To the mixture was added a solution of BuLi in hexanes (2
ml of a 1.5 M solution. 3.0 mmol) at room temperature, 40 min later the mixture was brought to
reflux for 30 min before being allowed to cool to room temperature. Benzyl bromide (0.34 ml.
0.49 g. 2.9 mmol) was added to the mixture and this was then heated under reflux for 90 min
before being allowed to cool. The THF/hexanes were removed in vacuum to give an orange
tar. To this was added water (0.5 ml) and then ether (30 ml), this dark green mixture was then
dried with MgSO. before being filtered through MgSO •. The ether was removed in vacuum,
and the residue was dried in high vacuum. Recrystallization from ethyl acetate gave 42 as an
orange solid (0.58g. 1.28 mmol. 44 %). A concentrated solution of 42 in hot ethyl acetate and
allowed to cool very slowly (Flask placed in a Dewar flask containing hot water, with the top
plugged with cotton wool), before being allowed to stand undisturbed for many days. Much of
the 42 decomposed to a brown solid but a crystal suitable for single crystal X-ray diffraction
study was obtained. m.p.l00-l04°C. (Found: C, 61.0; H, 5.4; N, 0.0. C23H25FePS2 requires C,
134
61.1; H, 5.6; N, 0.0). IR 1649w, 1632w, 1597m, 1492m, 1452m, 1427m, 1409m, 1384m,
1372m, 1365m, 1350w, 1312w, 1244w, 1231m, 1193m, 11775, 11685, 1135w, 11075, 1067m,
1051w, 1031m, 10195, 1001m, 946w, 9015, 843m, 831w, 8235, 7945, 774m, 729m, 7055,
6935, 6585, 6215, 593m, 569m, 521m, 504m, 4925, 4845, 4755, 4555, 415w, 385w, 373m,
333w, and 321w (cm·'). op, 51.3 ppm. OH (ppm), 7.2 (4H, m), 5.9 [lH, d 3J("P-'H)=26 Hzj, 5.0
(lH, 5), 4.9 (lH, 5), 4.52 (lH, m), 4.44 (lH, m), 4.36 (2 H, m), 4.2 (5H, 5), 4.1 (2 H, m), 1.9 (3
H, 5), 1.7 (3 H, 5). On closer examination of the peak at 4.1 ppm, it appears to be a pair of
doublets that a poorly resolved. oc, 158 (quat), 141 (quat), 129, 128, 127, 123, 121, 116 (CH,),
72 (m), 70 (Cp), 36, 26 [d J(PC) 18 Hz], and 21. MS(EI+) mlz 452 (M+), 330(M-C7HsSt,
314(M-C.HlOS), 248, 232, 217, 186, 155, 121,91,65,51,39 and 31. Molecular ion found at
412.0173, 12C,,'H,566Fe31p3'S, requires 452.04842 (error of 0.4 ppm). CV reversible redox
couple at 0.66 Volt.
Synthesis of 178
The above synthesis was repeated using 41 (0.50g) and l-methyl-2-bromomethylbenzene
(0.18 ml. 0.26g. 1.4 mmol) in place of the benzyl bromide to furnish P-ferrocenyl P-(2-
methylphenyl)methyl sulfide P-2,3-dimethylbuta-l,3-dien-lyl phosphine sulfide (178) as an
orange solid (152 mg. 326 mmol. 23%) after recrystallization. In this experiment Celite was
used as a filter aid for the filtration of the ether solution of the raw product. The recrystallized
product contained a small trace of impurities including a trace of ethyl acetate even after
drying in high vacuum. After a second recrystallization, the product was dissolved in CDCI3
before removal of solvent in vacuum to yield an orange solid (89 mg. 191 flmol. 14 %). m.p.,
105-110°C. (Found: C, 60.7; H, 5.8. C'4H'7FePS, requires C, 61.8; H 5.8%). IR 3086m,
29755,29505,29165, 2850m, 1596m, 1492m, 1430m, 1411m, 1384w, 1233w, 11685, 1108m,
1049w, 1031m, 10195, 1002m, 9035, 851w, 841w, 8225, 793m, 774w, 7325, 6895, 6585,
6205, 593m, 565m, 536m, 520m, 4905, 4565, and 445m (cm·'). op 51.3 ppm. Oc (ppm), 158.7,
143.7,137.5,130.8,130.7,128.0,126.5,122.9,122.0, 116.7 (CH,), 73 to 71 (m), 70.7 (5, Cp),
34.7 (CH,), 26.7 [d J(PC) 19 Hzj, 21.9, and 19.7. OH (ppm) 7.2 m, 7.0 m the total integration for
aromatic area is (5 H), 5.9 [lH, d 'JeH-31 p)=25 Hzj, 5.0 (1 H, 5), 4.9 (1 H, 5),4.6 (1 H, 5), 4.5
(1 H, 5), 4.4 (2 H, m), 4.2 (5 H, 5), 4.0 (2 H, m), 2.3 (3 H, 5), 1.9 (3 H, s), 1.7 (3 H, 5). On
closer examination the complex peak in the 'H spectrum at 4.0 ppm was shown to be a pair of
doublets of doublets. Lines were observed at the following chemical shift values (ppm) 4.082,
4.061,4.052,4.031,4.022, 3.998, 3.992, and 3.968.
135
Centre of multiplet 0 (ppm) Nature of coupling J (Hz)
3.99 'H-'H 11.9
4.06 'H-'H 11.9
3.99 3'P_'H 9.8
4.06 3'P_'H 8.3
MS(EI) rnIz 466 (M+), 331, 328, 296, 248, 217, 186, 144, 129, 105, and 91. Molecular ion
found at 466.0641, 12C2.'H27S"Fe3'p32S2 requires 466.0641 amu (within 0.1 ppm).
Synthesis of p-Ferrocenyl P-(2,3-dimethYlbuta-1,3-dien-1-YI) P-2,4-dinitrophenyl sulfide
phosphine sulfide. (179)
The above synthesis was repeated using 41 (0.601g. 1.66 mmol), and with l-chloro-2,4-
dinitrobenzene (0.5g. 2.5 mmol) being used instead of a benzyl halide. After one hour of
heating under reflux, following the addition of the dinitrochlorobenzene a small sample was
tested with water, no green compounds were formed. After removal of all solvent, the red
product was dissolved in hot ethyl acetate before being allowed to cool, after filtration a red
solid was obtained by the removal of the ethyl acetate. This residue was washed with ether
(50 ml) to give a copper coloured solid (0.411 g). To a solution in dichloromethane was added
ether to furnish 179 as a copper coloured solid (218 mg. 413 J.lmol. 25 %). IR 3098m, 3078m,
2975w, 2915w, 2854w, 1595m, 15415, 15245, 1459w, 1438w, 1410w, 1350s, 1194w, 1172m,
1106m, 1038m, 1023m, 914w, 901s, 831s, 760m, 739s, 703m, 662w, 638m, 619w, 571w,
522w, 498m, 466m, 456m (cm"). op 60.0 ppm. OH (ppm) 8.59, 8.31 total for the last two peaks
(3.0H), 6.0 [lH, d 2J[31 p_'Hj=28 Hzj, 5.09 and 5.01 the total of the last two peaks is (3H), 4.5
to 4.3 (m), 4.28 (s). Integration total for ferrocenyl area (4.5-4.2 ppm) is 9H, 2.08 (4H, s), 1.89
(4.0, s). MS(EI) rnIz 528 (M+), 364, 329, and many ions below 290. Molecular ion found at
528.0028, 12C2,'H2,56Fe14N,'"O;'p32S2 requires 528.0029 (error of 0.2 ppm). Reversible
redox couple at 0.69 Volt.
The reaction of benzaldehyde with FC2P2S ••
FC2P2S, (4.09 g. 14.6 mmol) and benzaldehyde (1 ml. 1 g. 9.7 mmol) were heated under reflux
in xylenes (50 ml) for 30 minutes. After cooling and stirring overnight the mixture was applied
to a flash column (50 g Si02). This column was eluted with 100 ml petrol, 500 m140% CH2CI2
in petrol, 500 ml CH2CI2 in petrol followed by 750 ml CH2CI2. The first orange group of
fractions were combined and evaporated to form an orange solid (2.8 g). Examination of this
solid with 3'P-{'H} NMR spectroscopy reveals the presence of FC,P303S3 and another
phosphorus compound. This solid was heated with ethyl acetate (50 ml) and allowed to cool
before being collected by filtration. This solid was then recrystallized from ethyl acetate (circa
110 ml) to give 45 as an orange solid (574 mg. 1.10 mmol. 8 %). m.p. 189-190°C. (Found: C,
136
----- - - - - ------
55.5; H, 3.8; N, 0.0. C2.H2,FePS. requires ;C, 55.0; H, 4.0; N, 0.0%). IR 3083m, 3026m,
2916m, 1801w, 1736w, 1595w, 1582w, 1492m, 1452m, 1408m, 1386w, 1363m, 1348w,
1332w, 1238w, 1192m, 1177s, 1169s, 1107m, 1072m, 1052w, 1027s, 1002m, 915w, 897w,
842m, 828s, 797w, 781m, 724s, 703vs, 666s, 614m, 682m, 537s, 515s, 487s, 473s, 400w,
323m, 302w, 285w, 260w, 252m, and 241w (cm·'). lip 72.0 ppm. IiH (ppm) 7.5 (4H, m), 7.4
(6H, m), 6.25 [2 H, d, 3J(31 p_'H)=10 Hzl, 4.88 (2H, m), 4.62 (2H, m), and 4.43 (5H, s). lie
(ppm) 129.2,129.1,128.0,72.5 (d, 13 Hz), 71.8 (d, 16 Hz), 70.6, and 58.0. MS (FAB) m/z
524,490,413,402,391,371,349,315,303,280, and 259. The expected isotropic distribution
was observed for the molecular ion. CV Redox couple at 0.76 volt showing slight signs of slow
electron transfer.
The reaction of tert-butylaldehyde (pivaladehyde) with FC2P2S.
FC2P2S. (6.2 g. 11 mmol) was partially dissolved in hot toluene (50 ml) and allowed to cool
before the addition of THF (10 ml) and teft-butyl aldehyde (1.6 ml. 1.27 g. 14.7 mmol). The
mixture was slowly brought up to a gentle reflux for 14 hours before being allowed to cool.
Before chromatography (74 g SiO, 30 % CH2CI, in petrol), after removal of solvent a yellow
orange solid remained. This was recrystallized from ethyl acetate. Examination with 31 P-{' H}
NMR spectroscopy revealed the presence of FC3P30 3S3. By cooling a hot solution a crystal
suitable for X-ray crystallography was obtained. After two further second recrystallizations
from ethyl acetate 46 (37 mg. 76.4 Ilmol. 1 %) was obtained as a yellow solid.
(Found: C, 49.1; H, 5.9. C,oH'9FePS. requires C, 49.6; H, 6.0%). IR 3114w, 2957s, 2928m,
2898m, 2864m, 1474m, 1462m, 1411w, 1396m, 1390m, 1367s, 1314w, 1228m, 1200w,
1195w, 1182m, 1172s, 1107m, 1055w, 1029m, 1020m, 1000m, 936w, 912w, 897w, 873w,
842m, 827s, 814w, 778m, 769sh, 735w, 703s, 666vs, 618m, 541m, 530s, 489s, 478s, and
330m (cm·'). lip 72.3 ppm. IiH (pp m) 5.02 [2 H, d, J(PH)11 Hzl, 4.85 (2 H, m), 4.48 (2 H, m),
4.43 (5 H, s), and 1.22 (18 H, s). lie (ppm) 72.5 to 72.0 (m), 70.7 (s), 68.1 Id, J(PC)2 Hzl, 37.5
Id, J(PC)6 Hzl, and 28.5. MS(FAB+) mlz 484, 452, 401, 280, 248, 217, and 186. Expected
isotropic distribution observed for the molecular ion.
The reaction ofN-benzylidene benzyl amine with Fc2P,s •.
FC2P2S, (4.4 g. 7.86 mmol) and N-benzylidene benzyl amine (153) (1.54 g. 7.89 mmol) were
heated in toluene (80 ml) and xylene (80 ml) for 45 hours. After cooling this mixture was
filtered through a silica pad and this pad was washed with CH2CI, until the filtrate is no longer
coloured. After removal of solvent, chromatography (60 g silica elution with 1.5 L 40% CH2CI2
in petrol followed by 350 ml CH2CI2) gave fractions containing only two compounds in large
amount. Evaporation of these gave a brown solid (2.4 g). This was extracted with hot ethyl
acetate before being allowed to cool, to form an orange solid (0.94 g), further chromatography
(12 g silica. Elution with 500 ml 30% CH2CI, in petrol) gave after removal of solvent 3-benzyl-
137
2,4-diferrocenyl-1,3,2,4-thiazadiphosphetane 2,4-disulfide (183) as an orange solid (0,489 g.
772 !lmol. 10 %). m.p. circa 150-160·C. (Found: C, 52.0; H, 4.1; N, 2.3; S, 15.4.
C27H25Fe2NP2S3 requires C, 51.2; H, 3.9; N, 2.2; S, 15.2%). IR 3077w, 3027w, 2919w,
2858w, 1494w, 1455m, 1445w, 1410m, 1390m, 1366m, 1351m, 1315w, 1244m, 1205w,
1195m, 1182s, 1121s, 1105m, 1024s, 998s, 913m, 857s, 843s, 816s, 799s, 7685, 734m,
696m, 681vs, 655m, 613w, 576m, 518m, 504m, 493s, 481m, 462s, 414m, 345w, and 329w
(cm-'). cSp (ppm), 65.1. cSH (ppm), 7.2 (2H, m), 7.0 (3H, m), 4.89 (2H, m), 4.68 (2H, m), 4.55
(2H, m), 4.44 (2H, m), 4.33 (10H, s), 4.16 (2H, s). cSc (ppm), 129.1, 127.9, 127.3,76.5 [d J(PC)
20 HzJ, 73.5 Id, J(PC) 14 HzJ, 72.2 [d J(PC) 14 HzJ, 71.6 [d J(PC) 17 HzJ, 70.3, and 46.9
(CH2). 'H_13C correlation 'H cS(ppm) ['3C cS(ppm)J 7.2 [129.1], 7.0 [127.9J, 7.0 [127.3J, 4.68
[76.5J, 4.55 [73.5J, 4.44 [72.2J, 4.89 [71.6J, 4.33 [70.3J and 4.16 [46.9J. MS(FAB) m/z 656
(M+Na(, 634 (MH(, 633 M+, 617, 601,568,513,492, and 353. CV Reversible couple at 0.80
volt, with second waves observed on the leading edges of the couple.
A second fraction that was a mixture of two compounds was then obtained. A third fraction
was obtained which is almost pure 152 . Evaporation of this fraction gave 152 as a yellow
solid (112 mg. 236 !lmol. 1.5 %). From a dichloromethane solution orange crystals were
obtained. Using one of these crystals a molecular structure was obtained by means of a X-ray
diffraction experiment. (Found: C, 58.6; H, 4.3; N, 0.0; S, 19.9 C2.H2,FePS3 requires C, 58.6;
H, 4.3; N, 0.0; S, 19.5%). IR 3080m, 3025m, 2923m, 2853m, 1493m, 1449m, 1408w, 1385w,
1366w, 1338w, 1312w, 1284w, 1214w, 1196w, 1183w, 11705, 1107m, 1076m, 1031m, 1016s,
1007m, 971w, 916w, 887w, 8475, 836m, 827w, 8165, 766s, 757m, 743m, 7005, 6925, 670vs,
6445, 621sh, 5985, 5375, 4955, 479s, 398w, 378w, 363w, and 325m (cm"). cSp (ppm), 86.3. cSH
(ppm), 7.1 (10 H, m), 5.21 [2H, d J(PH) 14 HzJ, 4.77 [2H, d J(PH) 1.5 Hz], 4.54 [2 H, d J(PH)
1.5 Hz], 4.32 (5 H, s). cSc (ppm), 153.4 (quat), 135.5 (quat), 130.0, 128.9, 128.4.73.5 Id, J(PC)
21 HzJ, 73.3 Id, J(PC) 17 Hz], 71.3 and 67.7. MS(FAB) miz 492, and 391. MS(ES+) m/z 515
(M+Na(, 493 (M Ht, 301, 267, 239, 217, 205, 186, and 149. MS(ES-) rnIz 491 (M-Hr. CV,
Reversible redox couple at 0.71 volt.
138
Chapter 6
Reactions of Dithiadiphosphetane Disulfides With Organonitrogen Compounds
Section 6.1 Introduction
Nitrogen phosphorus sulfur compounds have been investigated as ligands'5 •. '57,
insecticides, '58 fungicides, '59 herbicides '58 and antibacterials'60 Since many nitrogen
phosphorus sulfur compounds have been made from Lawesson's reagent (Figure 6.1), the
question of how the presence of a ferrocenyl group would mOdify the chemistry arose. Another
goal was the synthesis of new
dithiadiphosphetane disulfides.
nitrogen phosphorus sulfur compounds from
Me0"©l OilS
P-S I I
Sl"©l Figure 6.1 Lawesson's reagent.
OMe
The reactions of nitrogen compounds with dithiadiphosphetane disulfides include (i) the
reaction with nitrogen nucleophiles, such as the reaction of aniline with Lawesson's reagent
(Equation 6.1 a)'·' (ii) Transformations that could be a series of pericyclic reactions, such as
the reaction of azides '56 and isocyanates '62 with dithiadiphosphetane disulfides to give
thiazadiphosphetanes (Equation 6.1 b).
NCO
© .. S
An, II P-S I I S-P
Equation 6.1 b II 'An S
LR
err lVJ /P-NHPh .. An \
NHPh Equation 6.1 a
There are some reactions for which two mechanisms could be suggested, one pericyclic and
the other stepwise, for example the reaction of benzil dianils with Lawesson's reagent.'·3 This
139
reaction could be a concerted [4+2] Diels-Alder reaction (Equation 6.2a), instead of the
stepwise mechanism (Equation 6.2b) in the literature. 163
Ph I
Ph N
Xr\ n) Ph N:------;,;P
I S"" 'An Ph
Ph I
PhXN, [2+4] S -~ .. ~ I Equation 7.2a /p,
Ph N 11 An I S Ph
r Ph
In .. Ph
AN".S3
Equation 7.2b . ~ I Ph ~iI'An
I S Ph
Most of the reactions of eN double and triple bonds with dithiadiphosphetane disulfides
studied in this work are thought to be pericyclic reactions, or a series of pericyclic reactions.
All the NPS rings synthesised in this work, other than the thiadiazaphosphorines, are
saturated rings that do not have " electrons. Unsaturated rings such as the reactive anti
aromatic 1,2-azaphosphete (1-aza-2-phosphacyclobutadiene) are known. '64 Due to the poor
,,-orbital overlap between phosphorus and carbon, these compounds are more stable than
cyclobutadienes (Scheme 6.1 ).'64
R, MeOOC COOMe P-N3 ~
R/ [2+41
•
N~ 11" '-N\I
R,P) "~N MeOOC COOMe
l-N'
Rg MeOOC COOMe
Scheme 6.1 Reaction of Ph,PN3 with DMAD followed by treatment with piperidine. 164
140
The reaction of 1,3-dipoles with dithiadiphosphetane disulfides affords compounds with five
membered rings. An example would be the reaction of Lawesson's reagent with benzo
phenylhydrazonoyl chloride (Scheme 6.2).'65 Bent 1,3 dipoles can be reacted with Lawesson's
reagent to give adducts of the dithiophosphine ylide.'66
S S R \\/ " I P P / "S/ \\
R S
R can be Me, Et or p-MeOCeH4
.. -HCI
1
Scheme 6.2 Reaction of dithiadiphosphetane disulfides with benzo-phenylhydrazonoyl
chloride.'65
The reaction of a variety of dialkyl cyanamides with dithiadiphosphetane disulfides was
reported to give 1 ,3,5,2-thiadiazaphosphorine-6-sulfides '67.'68 in 100% yield, and this reaction
was thought to be a stepwise reaction starting with the attack of a cyanide nitrogen on the
phosphorus atoms.'6B The product of this reaction has been reported to be a plant protection
agenl.,67 It was decided to repeat this work as the results presented in the literature were not
completely convincing. Interestingly the reported formation of the 1,3,5,2-
thiadiazaphosphorines formed from dialkyl cyanamides and dithiadiphosphetane
disulfides'67.'68 contrasts with the formation of 1,4-thiaphosphorines from electron-rich
alkynes"B.19 (Scheme 6.3).
141
R can be Et, Ph, An or SPh.
R'2N can be
Scheme 6.3 Reported reactions of LR with electron-rich acetylenes and dialkyl
cyanamides."8.11 •. ,67.'"
Section 6.2 Results and Discussion.
The Reactions of Dialkyl Cyanamides with Dithiadiphosphetane
Disulfides
The synthesis of a 1,3,5,2-thiadiazaphosphorine ring from diferrocenyl dithiadiphosphetane
disulfide and dimethyl cyanamide (184) was attempted (Equation 6.3).
S Fc \\ /
4 Me2N'--==N P W/ 'S
FC2P2S. X")l J Me2N ~NMe2
Equation 6.3
Using literature conditions for a similar reaction, '67.'" from Fc,P,S. and 184 a dark yellow
solid was obtained. Flash column chromatography gave 94 as a bright yellow solid (57 %)'6.
While the phosphorus chemical shift of 94 (op 61.8 ppm) is similar to the chemical shifts
reported for the 1,3,5,2-thiadiazaphosphorines (56.5 to 68.5 ppm), '67 in the 'H NMR spectrum
instead of 2 distinct methyl environments a single peak (OH 3.11 ppm) was observed. For a
1,3,5,2-thiadiazaphosphorine-6-sulfide two environments in the ring and two methyl carbon
environments would be expected, but only one environment was found for each of these two
types of carbon (oc ring 154.8 and Oc methyl 37.4 ppm) (Figure 6.2)'6. One explanation for
these NMR spectroscopy results would be that the molecule has a greater symmetry than the
1,3,5,2-thiadiazaphosphorine would have. A 1,3,5,4- or 1,2,6,4-thiadiazaphosphorine would
have half as many alkyl and heterocyclic chemical environments as the 1,3,5,2 isomer. The
absence of a strong coupling between the phosphorus and the heterocycles carbons suggests
that the product is not the 1,2,6,4 isomer. "
142
I 160
I 140
I 120
I 100
11 I
BD Figure 6.2 The 13C-{' H} NMR spectrum of 94.
I 60
I 40
Isomers of the thiadiazaphosphorine ring that would have two 'H dimethylamino and ring 13C
environments, which are inconsistent with the NMR spectroscopic results, shown in Figure
6.3.
p w'" '8
A J Me2N ~NMe2
Figure 6.3 Thiadiazaphosphorines with two environments for the ring carbons and the
dimethylamino groups.
The 'H and 13C-{'H} NMR spectroscopy indicates that 94 only has one environment for the
dimethylamino groups and the ring carbon. Both of the isomers in Figure 6.4 would have the
correct number of chemical enviroments.
Figure 6.4 Thiadiazaphosphorines with one environment for the ring carbon and
dimethylamino groups. 143
X-ray crystallography confirmed that 94 is a 1,3,5,4-thiadiazaphosphorine-4-sulfide (Figures
6.5, 6.6 and Table 6.1 )'8. The thiadiazaphosphorine is almost symmetric boat shaped ring,
with the sulfur and phosphorus atoms 0.48 and 0.30 A respectively above the C(1)-N(1)-C(2)
N(2) plane, while N(3) and N(4) are 0.16 and 0.25 A below this plane. The dimethyl amino
groups are planar suggesting that they are participating in some delocalization. The exocyclic
sulfur and the ferrocenyl group are occupying approximately axial and equatorial sites. The Cp
rings of the ferrocenyl group are twisted by 72° with respect to the C2N2 plane of the
thiadiazaphosphorine ring.
c
c
81
c
c
Figure 6.5 Molecular structure of compound 94.
S Me2Ny N ..... U
P-Fc I SyN
NMe2
Figure 6.6 Compound 94.
144
c
Table 6.1 Selected bond lengths (A) and angles (0) found in the molecular structure of 94.
P(1 )-S(1) 1.941(2) S(1 )-P(1 )-N(1) 114.6(2)
P(1 )-N(1) 1.648(4) S(1 )-P(1 )-N(2) 113.6(2)
P(1 )-N(2) 1.664(4) S(1 )-P( 1 )-C(7) 111.1(2)
P(1 )-C(7) 1.783(5) N(1)-P(1)-C(1) 104.4(2)
N(1)-C(1) 1.289(6) N(2)-P(1 )-C(7) 103.9(2)
N(2)-C(2) 1.290(6) P(1 )-N(1 )-C(1) 122.6(4)
C(1 )-S(2) 1.788(5) P(1)-N(2)-C(2) 121.0(4)
C(2)-S(2) 1.771(5) N(2)-C(2)-S(2) 127.3(4)
N(3)-C(1 ) 1.335(6) N(1)-C(1)-S(2) 125.4(4)
N(4)-C(2) 1.365(6) N(1 )-C(1 )-N(3) 122.0(5)
N(2)-C(2)-N(4) 119.6(5)
C( 1 )-S(2)-C(2) 101.0(2)
S(2)-C(1)-N(3) 112.5(4)
S(2)-C(2)-N(4) 113.1(4)
The P=S bond length in 94 is not significantly different to that in FC2P2S" Both P-N distances
are shorter (mean P-N length is 0.144 A shorter) than the sum of the covalent radii (1.8 A)
suggesting both bonds have some 1t character. 31,103
The reaction with dimethyl cyanamide (184) was repeated for Lawesson's reagent (LR) to give
a modest yield of a similar 1 ,3,5,4-thiadiazaphosphorine (185) (31p-{'H), 'H, and 13C-CH} NMR
spectroscopy are all in agreement with structure) (Figure 6.7).
Figure 6.7 Structure of 185
The synthesis of a 1 ,3,5,4-thiadiazaphosphorine has previously been reported by the reaction
of a P,P-diisocyanate with bis-(trimethylsilyl) sulfide,17o and the related heterocyclic system,
the triazaphosphorine has been prepared (Scheme 6.4).171
145
P(X)CI3
X= 0 orS
S 11 P +
Me/ ,'NCO NCO
NH
•
NHR NH
CH2CI2 OOC R' N==< A NMe2 , I RHN NHR 1
--------_.. 'P NH. P
1. A RHN NHR
II \ ==< 40-60 oC Me2N/ 'NMe2 2.'" (X =0 1100 C, X =S 1400 C) X N
NHR
Scheme 6.4 Synthesis of a thiadiazaphosphorine and triazaphosphorines.
The reaction of Fc,P,S. and 184 was repeated on a larger scale at a lower temperature.
Besides 94, a second compound (95) was isolated (15%), as a red oil which on standing
became a solid (Figure 6.8)'·9 3'p-{'H} NMR spectroscopy indicated this to have a single
phosphorus environr:nent (op 67 ppm), and 'H NMR spectroscopy (OH 2.6 ppm) suggested that
the compound has methyl groups where the 31p_'H coupling (14 Hz) was much greater than
that in the thiadiazaphosphorine.
S 11
FC-P-NMe2 1 NCS
Figure 6.8 Structure of compound 95.
Schmidipeter et al. described the reactions of dithiadiphosphetane disulfides with dialkyl
cyanamides R2NCN (R2 being cyclo-C.H"
, Et or "2 piperidinyl)'·7.168 The electronic
differences of these alkyl groups and the methyl group is likely to be negligible while the
methyl group exerts a smaller steric effect. To test if the outcome of the reaction is dependent
on the nature of the alkyl groups, the reactions of piperidine-1-carbonitrile (186) with Fc,P2S.
and LR were performed. Both reactions gave 1,3,5,4-thiadiazaphosphorines (187) and (188)
and P-isothiocyanates (189) and (190) as products (Scheme 6.5).
The 31 P and 1 H NMR spectroscopy for the thiadiazaphosphorine from LR were identical with
that reported in the literature ,.7 suggesting that the isolated compound was the same as that
in the original report. The interpretation in the literature of the 'H NMR spectrum is surprising,
since the 13C-{'H} NMR spectrum obtained in this work suggests the piperidinyl groups are
146
identical. Apart from the thiadiazaphosphorines and isothiocyanates (94, 95, 185, 187, 188,
189 and 190) traces of other compounds were isolated which could not be identified.
On changing from dimethyl amino groups to piperidinyl groups little change was seen in 8p or
u(P=S) values (Table 6.2). The NCS group 8c chemical shifts of 95 and 189 (144 and 145
ppm) are similar to that reported for PhNCS (136.0 ppm) (Table 6.2).172
S S Fc 11 \\ / P P
Me2W .... I ....... NCS W""' ....... ~ Fc )l~
95 ON R=~C187 0 R = An 188
S 11 P
O/k'NCS
R = Fc 189 R=An190
Scheme 6.5 1 ,3,5,4-Thiadiazaphosphorines and P-isothiocyanates.
Table 6.2 Selected spectroscopic data for thiadiazaphosphorines and P-isothiocyanates.
Compound 8p (ppm)
94 61.8
95 67
185 58.2
187 61.6
188 58.1
189 63.3
190 60.2
8c (NCS) (ppm)
144
145
a
u(P=S) (cm·i )
680
671
691
a
a
678
689
a: Value missing because measurement was not performed or because of spectral
congestion.
The 31 p chemical shifts for the compounds in Table 6.2 are all higher field than all the following
compounds in which a phosphorus atom is bonded to a ferrocenyl group, two dialkylamino
groups and a doubly bonded sulfur,173 suggesting that the factors influencing 8p are not based
simply on the electronegativities of the attached groups (Scheme 6.6)
147
Me Me S Me
S I \ ~II I S~/NJ P-N IIt
N] Me-J~ Fc-P, "P
N Fc/ 'N Fe I MI ~s Me Me 11 I
82.3 80.1 P-N
Me-J~ 78.1
Me
~b ~fl r-NR2 NR, 5p R,N
FeMe Fe NEt2 78.1
~s~e ~s NMe2 82.3
MeJ:) 11 Piperidinyl 77.0 r-NR2
R,N
77.8
Scheme 6.6 P-Ferrocenyl phosphorus nitrogen sulfur compounds with op values.
While in the proton NMR spectrum of 95 the peaks for the N-methyl groups are simple
doublets, in the 'H spectrum for 189 a complex peak is present at 3.2 ppm (Scheme 6.7). By
irradiation of the alkyl proton environment at 1.5 ppm, the multiplet is simplified to a pair of
doublets of doublets (Scheme 6.7).
I 3.4
Normal
I 3.2
(ppm)
I 3.0
With double irradiation
I~--------~I----------~I ---3.4 ()3.2 3.0
ppm
Scheme 6.7 Partial'H spectra of 189. 148
A geminal coupling ('J['H-'Hj=12.6 Hz) between the axial and equatorial protons in the
piperidinyl group on atoms 2 and 6 is present. Two different phosphorus-proton couplings
exist; 10.2 Hz for the multiplet centred at 3.2 ppm and 9.8 Hz for the peak centred at 3.2 ppm.
These 31 P-'H coupling constants are similar to the coupling constant in 95. Infrared
spectroscopy clearly indicates the presence of an isothiocyanate group in 95, 189 and 190
(u(NCS) 2031 cm") (Figure 6.9).'74
,4j
90
80
70
60
%T 40
30
20
10
o vNCS
2022cm·1 ·12.1 +--~ ______ ~ ______________________ ~
2197.6 2000 1800 1600 1400 1200 1000 800 600 400 318.5 =-1
Figure 6.9 Infra-red (2200-220 cm") spectrum of 189.
X-ray crystallography confirms the structure of 95 as containing both a P-isothiocyanate and a
P-dimethylamino group (Figure 6.10 and Table 6.2).'69
149
Figure 6.10 Molecular structure of compound 95.
Table 6.2 Selected bond lengths (A) and angles (0) found in the molecular structure of 95.
S(1 )-P(1) 1.914(2) S(1)-P(1)-N(1) 113.2(2)
P(1)-N(1) 1.631(4) S(1)-P(1)-N(11) 112.2(2)
P(1)-N(11) 1.700(5) S(1 )-P(1 )-C(1) 116.7(2)
P(1)-C(1) 1.766(5) N(1)-P(1)-N(11) 104.9(3)
N(1)-P(1)-C(1) 107.3(2)
N(11)-P(1)-C(1) 101.2(2)
P(1)-N(1)-C(12) 120.0(4)
P(1)-N(1)-C(13) 121.0(4)
C(12)-N(1 )-C(13) 113.2(5)
In 95 the P(1)-N(1) bond is shorter (1.631(4) A) than P(1)-N(11) (1.700(5) A), due to
differences in the electronegativties of the NMe2 and NCS groups. The more electron-rich
group bonds more strongly to the phosphorus atom. N(1) is in an almost perfectly planar
environment, and this shape, combined with the shortened bond length, does suggest some
double bond character of bond P(1 )-N(1). The mean P-N bond length (1.66 A) for 94 is
midway between the values of P(1)-N(1) and P(1)-N(11).
The presence of sulfur and phosphorus at the 1,4 positions in the thiadiazaphosphorine ring of
94 posed a mechanistic challenge. The formation of the 94(and 187) and the 95(and 189) can
be explained as being via a thiazaphosphorane intermediate (Scheme 6.8).'69 The first step in
the above mechanism could be a thermal (21ts+21ta) 2+2 cycloaddition. The
thiazaphosphetane ring then opens thermally in a 41t electron process via a MObius transition
state. This ring opening process is favoured by the increased ring strain when compared with
the thiaphosphetanes, even while the thiazaphosphetane is stabilised by resonance (Scheme
6.9) .. After the ring opening the intermediate undergoes either a Diels-Alder reaction with
another molecule of the cyanamide, or a rearrangement to the isothiocyanate.
150
NR2
II~~-d Fc-P- -- - - --N
\\ S
! NR
Fc,I/l-JCS P
M
• 8 NR2
ft( Fc-P-N
11 S
! SyNR2
Fc, ",N p'" 11 S
NR2
~ de~NR' Fc", ",N
p'" II S
1 S Fc \\ /
P w/ 'N
Me2NAsANMe2
Scheme 6.8 Mechanism for the formation of 941187 and 951189 from Fc,P,S. and dialkyl
cyanamides.
S S S 8 S
11 11 11 8 1
R-!~ R-P-N R-P-N R-P=N
LJ( • • I~ • • ~~~ S ~ NR2 @NR2 @NR2
Scheme 6.9 Thiaphosphetane and thiazaphosphetane rings.
The stability of the isothiocyanates on silica was unexpected but not without precedent'"
Silica that is used for chromatography contains water and it has a large number of acidic sites
that could be expected to promote the attack of a nucleophile by protonation of the
isothiocyanate. Treatment of 95 with a mixture of THF and water 80:20 (by volume) for 30
days caused little change by TLC suggesting that the isothiocyanate group has special
protection against the action of nucleophiles. Sulfuric acid was added to the mixture and after
standing for a further 8 days little change was detected by TLC. The starting material was then
recovered unchanged, (88% recovery) (Equation 6.4).
Equation 6.4
151
In contrast to the sluggish· reaction of 95 and water, the reactions of 95 with isopropylamine
(Equation 6.5a) and 95 with methanol/Et3N (Equation 6.5b) occur more rapidly. The reaction of
isopropyl amine with 95 gave 191, believed to be a thiourea. The reaction of amines with 95
could be used as a method of functionalization, that could attach a spectroscopicaliy useful
group to amines such as the NH2 groups present as end groups in proteins. 172 A disadvantage
of using 95 as a derivatization reagent would be that 95 is produced as a racemic mixture, so
the reaction of 95 with an amino end group in a protein would give a mixture of two
compounds.
S >-N~ S S MeOH 11 FC"""'~'NHJlNH~ Mixture .. P .. Et3N Fc""'" \'NCS THF THF NMe2 NMe2
191
Equation 6.5a Equation 6.5b
Mass spectrometry by the electrospray method did not give evidence for the expected
molecular ion. However an ion corresponding to loss of hydrogen sulfide from the salt was
observed at miz 435 (ES+) (Scheme 6.10).
..
Scheme 6,10 Possible fragmentation of 191 during ES MS.
Diphenylphosphinothioyl isothiocyanate reacts with a range of nucleophiles. '75 Two different
reactions are possible. The isothiocyanate can act as a leaving group or Ihe nucleophile can
attack the electrophilic carbon of the isothiocyanate (Scheme 6.11 ).175
152
S S
[ ,",U '" 1 S S
11 MeOH 11 H,O Ph,P(S)NCS 11 11 Ph,P • Ph,P • .. Ph,P, /PPh, " El3N " El3N OMe N=C=S 0
! 1 eqiv. Me,NH H,O
S S S se 11 )l II~ Ph,P, • Ph,P,
N NMe, NMe, 1 H
Scheme 6.11 Reactions of Ph,P(S)NCS with oxygen and nitrogen nucleophiles.
The attack of oxygen nucleophiles at the phosphorus atom, is favoured by the oxophilic nature
of phosphorus. In contrast, diphenylphosphino isocyanate reacts with both water and amines
at the carbon of the isocyanate group, because the isocyanate is a more eleclrophilic. 175
By cyclic voltammetry a redox change at 0.87 V was seen for P-ferrocenyl bis-piperidinyl
thiadiazaphosphorine (187) besides the FcJFc· couple at 0.53 V (Figure 6.11). This could be
due to the oxidation of the thiadiazaphosphorine ring. The smaller peak to the right of the main
peak was postulated to be due to a redox reaction of the thiadiazaphosphorine portion of the
molecule.
1.3 1.1 0.9 0.7 0.5 0.3 0.1 E(V)
Figure 6.11 CV of 187.
To investigate the redox behaviour of the thiadiazaphosphorine ring, a CV experiment was
performed on 188, and this showed an irreversible electrochemical oxidation (Figure 6.12).
153
O.S E (V)
0.4
o
200
400
Figure 6.12 CV of 188.
By the square wave method, the redox potential for this change was measured as 0.67 V. This
oxidation could not be observed for a solution of anisole in the same redox range and thus it is
reasonable to assume the thiadiazaphosphorine ring is being oxidised. This oxidation of 188 is
much less reversible than the same oxidation of 187. This second oxidation is likely to be due
to an oxidation of one of the sulfur atoms, giving a radical cation which could undergo a
chemical change that removes it from the equilibrium.
The reaction of a bis(dialkylcyanamide) with a dithiadiphosphetane disulfide would give a
polymer incorporating carbon, nitrogen and phosphorus. This polymer with P-ferrocenyl
groups bonded to the phosphorus atom would be expected to be electrochromic. A polymer
that is noncrystaliine would be expected to be more likely to give a transparent film, than a film
grown of a more crystalline compound such as a simple thiadiazaphosphorine.
Piperazine 1,4-dinitrile was selected as a bis(dialkylcyanamide) because ring strain would
prevent both cyanamide groups from reacting with a single phosphorus centre to form a
heterocycle rather than a polymer. This starting material was prepared by the reaction of
piperazine with cyanogen bromide in acetonitrile in the presence of potassium carbonate.'76
It was found that when FC2P2S, and piperazine 1,4-dinitrile were reacted together in toluene
an insoluble product was obtained which could not be characterised. The insoluble nature of
this product prevented solution state NMR spectroscopy, chromatography and
recrystalJization. To prevent insoluble products forming on the surface of the reactants it was
decided that both reagents should be in solution before the reaction was started. The
dithiadiphosphetane disulfides are soluble in hot toluene while the piperazine 1,4-dinitrile is
soluble in hot acetonitrile. For the first such synthesis bis(3-tert-butyl-4-methoxyphenyl)
154
dithiadiphosphetane disulfide (LR') was selected because of the solubililsing effect of the aryl
groups. The reaction was performed by pouring a hot solution of the phosphorus sulfur
starting material into a hot solution of the bis-dialkylcyanamide. After heating the two together
for a short time, the mixture was allowed to cool before the removal of the solvents in vacuum.
This reaction gave 192, as a pale yellow solid, which was found by GPC to be a mixture of
oligomers. While the lengths of the chains were very short, the product does form transparent
films when a dilute solution is evaporated. IR spectroscopy revealed this solid to contain
isothiocyanate and nitrile groups. A major reason for the chain length being short is likely to be
the formation of the isothiocyanate as a termination reaction that prevents the polymer chain
from growing any further. By electrospray mass spectrometry short oligomers 193,194 and
195 were identified (Scheme 6.12).
Ar is 3-terl-butyl-4-methoxyphenyl
Scheme 6.12 Compounds observed by ES mass spectrometry in the mixture of oligomers.
The synthesis was repeated with a small amount of LR' replaced by Fc,P,S •. This gave an
orange solution that was almost perfectly clear. Evaporation of the solvent gave 196 as an
orange glass like solid, this is an oligomeric mixture similar to 192. Owing to such a short
chain length 196 is too short to be considered as a true polymer. 196 has been found to have
155
a low solubility in MeCN while in THF it is soluble so allowing the material to be processed into
films. To make an oligomer with more ferrocenyl groups, FC2P2S, was used as the sulfur
phosphorus starting material. The reaction gave a mixture of a dark insoluble solid and an
orange solution. After filtration and evaporation an orange tar was obtained. This tar was
dissolved in THF before being added to a large volume of petrol to give 197 as a fine orange
powder.
It is expected that by careful choice of precursors other structural features can be incorporated
into these oligomeric species. It is likely that the better method for the incorporation of many
functional groups would be to attach them to the bis-(dialkyl cyanamide). The advantage of
this site for the attachment would be that the functional group would not have to remain in
place during the synthesis of the dithiadiphosphetane.
Section 6,3
Electrochemical characterisation of mixtures 196 and 197
In acetonitrilefTHF solution 196 shows no peaks in its cyclic voltammogram, whilst as a
coating on a platinum wire it shows a redox couple. Oligomer 196 does not exhibit any
electrochromism visible to the eye.
A film of 197 was formed on a platinum electrode. This electrode was placed in an
electrochemical cell filled with a 0.2 M solution of Bu.NCIO •. This film was found to be
electrochromic. When reduced the film was light orange, but when oxidised the film became
black-green in colour. The colour change is reversible, but the change from black-green to
orange appears to be slower though this may be due to the intensely coloured nature of the
oxidised form. The polymer appears show signs of slow electron transfer due to some time lag
in the transfer of electrons from the ferrocenyl groups to the platinum electrode (Figure 6.13).
-2
o
2
0.2 o
Figure 6.13 CV for a coating of 197 on a Pt wire. 156
The electrode coating was very stable when immersed in MeCN. Four cyclic voltammograms
were recorded with no resting time between scans. Very little difference could be seen
between the different scans suggesting that the film was remaining stable. This experiment
was repeated with 20 scans, and very little change was seen between the scans. When the
electrode was immersed in a solution of lead perchlorate in 0.2 M Bu4NCI04, no difference
was seen. When an attempt was made to repeat this experiment USing aqueous 0.2 M KN03
as the electrolyte, the film decomposed rapidly.
It is expected that repeating the reaction using a tris(dialkylcyanamide) would give a product of
much greater molecular mass as it would now be a dendrimer. A suitable starting material
could be nitrogen mustard [N(CH2CH2ClhJ. This could be reacted with methyl amine and then
cyanogen bromide to give a tris dialkylcyanamide that could then be used for the synthesis of
a dendrimer. Nitrogen mustard is available from Aldrich. 177 Alternatively to increase the
molecular size, the polymer could be further condensed with a bifunctional second monomer
such as a diamine, using the isothiocyanate end groups present.
Section 6.4
The reaction of FC2P2S4 with dialkylcyanamides, where the
concentration of the dialkylcyanamide is small.
The literature 16. stated that the thiadiazaphosphorines were active as plant protection agents.
It is likely that under the reaction conditions used to make the thiadiazaphosphorines,,67.'6. p
isothiocyanates such as 95 could be formed. Phosphorus (V) isothiocyanates like 95, 188,
and 192 could after oxidation (Equation 6.6) in an insect, be active as acetylcholinesterase
inhibitors, which could make these desirable targets for synthesis. However the presence of
the P-ferrocenyl groups in 95 and 188 is likely to reduce their acute toxicity, as oxidation to
ferricenium salts would increase their water solubility. Which in turn would allow the compound
to be more readily excreted.
Equation 6.6
It was postulated that if the formation of 94 and 95 occurred via the mechanism suggested in
scheme 6.8, then the slow addition of 186 to a hot solution/suspension of a
dithiadiphosphetane disulfide would give a greater yield of 95 than would be formed by the
rapid combination of all the reactants followed by heating in small volume of solvent (Similar to
the method described in a patent).'6.
157
When a suspension of FC2P2S, in refluxing toluene was treated slowly with a dilute solution of
Me2NCN, a high yield of 95 and a small yield of 94 was obtained. This dependence of the
product distribution on the concentration of the dimethyl cyanamide is consistent with the
mechanism that has been proposed (Scheme 6.8). A similar experiment was performed where
the dimethyl cyanamide (186) was replaced by piperidine-1-carbonitrile (189). In this
experiment a 90% yield of the P-isothiocyanate (188) was obtained. Besides 94 and 95 an
additional product was isolated (by flash column chromatography). This product was a red oil
that solidified on standing. According to 31 p-{'H} NMR spectroscopy this solid is a mix1ure of
two compounds, the spectrum consisting of two pairs of doublets [3 J(31 p _31 p)"'44 Hz),
suggesting that two isomers were formed. By recrystallization (EtOAc) one of the two isomers
was obtained as an orange crystalline solid (198) [SPA 81.0, SPe 52.1, J(PAPe)=44 Hz) (Figure
6.14). The mother liquor did contain a mixture of the isomers, the second isomer [SPA 81.0,
SPe 53.2, J(P APe)=41 Hz) being the major component.
" 85 5'0 1i P-31 (ppm) i5 io
, 65 60 5'5
Figure 6.14 3'p-{'H} NMR spectrum of 198.
The 2J(31p _O_31 p) coupling constant of 41 Hz is similar to the 2J(31 p_N_31 p) coupling seen in
imidodiphosphinates (Figure 6.15 and Table 6.3).'58.'59
158
Figure 6.15 The structure of imidodiphosphinates.
Table 6.3 P-P coupling constants in imidodiphosphinates.
R R' E E' J(Hz) Reference
Ph Ph 0 L.P. 66 158 Ph Ph S L.P. 86 158 Ph Ph S Se 27 158 Ph Ph Se L.P. 93 158 Bu iso-Bu S S 26.4 159 Bu sec-Bu S S 30.8 159 iso-Bu sec-Bu S S 30.8 159 EtO Ph S S 22.0 159 EtO Ph S 0 17.6 159 EtO Ph 0 S 3.2 159
By maintaining a low concentration of the cyanamide, besides forming 95, the intermediate
thiazaphosphetane (Figure 6.16) has greater opportunity to react with another phosphorus
containing compound to give 198 which contains two phosphorus atoms.
Figure 6.16 The thiazaphosphetane sulfide intermediate.
According to mass spectrometry (m/z 614, M+) the molecular formula of 198 is
C23H24Fe2N20P2S3' The oxygen atom is thought to originate from a small trace of water that
was in the reaction mixture, or alternatively during the chromatography on silica a hydrolysis
or oxidation reaction could have occurred. As two isomers were formed initially it was thought
that some ring system might have been formed (Figure 6.17).
S Y Z S
\~/~ r't I X \ Fc Fc
n
S Y Z Fc
\~/~ r'rI / X \\ Fc S
n
Figure 6.17 Two isomers (cis and trans).
159
The presence of an isothiocyanate was clear from the infra red spectrum u(NCS)=2013 cm-',
suggesting that the product is unlikely to be a heterocycle. Like 95 and 188 the kinetic stability
of the above compound is surprising, since this compound had survived flash column
chromatography on silica. The following alternative structures for the formula
FC2P2(NCS)(NMe2)OS2 were then conSidered. The oxygen atom could be bridging the
phosphorus atoms (1) or doubly bonded to either of the phosphorus atoms (2 and 3.). Due to
the similar 3'P-{'H} NMR spectra the possibility of the oxygen being bonded to different
phosphorus atoms in the two compounds was eliminated (4.) (Scheme 6.14).
1. S S S S 11 11 "P~ ~P"
FC"'J' ~O~ ~"'Fc N N __
g /
11 11 ...... p~ ~P"
Fc"/ ~O' ~"'Fc N N __
g / M S S
11 S R R
S S S S 11 11
,.P~ ~P~ FC"'" ~o~ \""Fc
N N 11 / --C
11 11 P P
Fc";:" '0/ ',,"Fc N N __
11 / C
11 S S R
11 S R S
S 0 2. 11 11
,.P~ ,p" FC"'" ~S' ~"'Fc N N __
11 / C 11 S
3. ~ TI ,.P~ ~P"
Fc"'" ~S~ ~"'Fc N N __
11 / C 11 S
o S 11 11
...... p~ ~p" Fc" ---- ~S' ~"'Fc N N __
11 / C 11 S
4. 0 S 11 11 P P
FC"J 'S/ ~FC
11 / --C 11 S
S 0 11 11 P P
Fc/; 'S/ "Fc N N __
11 / C 11 S
Scheme 6.14 Possible isomers for the formula FC2P2(NMe2)(NCS)OS2 (198).
160
As two distereoisomers were formed in approximately equal amounts, the possibility of only a
single isomer being formed and then being thermally isomerised to give the mixture was
considered. This was discounted, as heating 198 at reflux in toluene for 24 hours did not
induce isomerisation. No formation of the second distereoisomer was detected by 3'p-{'H}
NMR spectroscopy.
Crystals of compound 198 suitable for X-ray analysis were obtained by the slow cooling of a
hot solution in EtOAc. The crystals are a mixture of the RR and SS distereoisomers (Figure
6.18 and Table 6.4).
Figure 6.18 Molecular structure of compound 198.
161
Table 6.4 Selected bond lengths (A) and angles (0) found in the molecular structure of 198.
S(1 )-P(1) 1.919(2) S(1 )-P(1 )-0(1) 114.3(2)
S(2)-P(2) 1.905(2) S(1)-P(1)-N(1) 113.7(2)
P(1)-0(1) 1.632(4) S(1)-P(1)-C(4) 115.7(2)
P(2)-0(1) 1.581(4) 0(1)-P(1)-N(1) 106.5(2)
P(1 )-N(1) 1.623(5) 0(1)-P(1)-C(4) 98.1 (2)
P(2)-N(2) 1.662(5) N(1)-P(1)-C(4) 107.0(3)
N(1 )-C(1) 1.472(8) S(2)-P(2)-0( 1) 113.6(2)
N(1 )-C(2) 1.459(8) S(2)-P(2)-N(2) 112.9(2)
S(2)-P(2)-C( 14) 118.2(2)
0(1 )-P(2)-N(2) 102.1(2)
0(1 )-P(2)-C(14) 103.9(2)
N(2)-P(2)-C(14) 104.5(3)
P(1)-0(1)-P(2) 137.9(2)
P(1 )-N(1 )-C(1) 123.2(5)
P(1)-N(1)-C(2) 120.0(4)
C(1 )-N(1 )-C(2) 113.1(5)
P(2)-N(2)-C(3) 163.7(6)
S( 1 I-PI 1 )-P(2)-S(2) 150.8
In 198 the P(1)-0(1) bond length is similar to the mean P-O bond length in 148 [1.632(5) A]
while P(2)-0(1) is shorter. The P(1)-N(1) and P(2)-N(2) lengths are not significantly different
from the distances P(1 )-N(1) [1.631 (4) A] and P(1 )-N(11) [1.700(5) A] found for 95. Like 95 the
nitrogen of the dimethyl amino group is almost planar, suggesting some donation of the lone
pair electrons to the phosphorus. The molecule is arranged in the solid state such that the
P=S groups are approximately anti (torSion angle 150.8°). This suggests no intramolecular
sulfur-sulfur attractive interaction to be occurring, no intermolecular sulfur-sulfur interactions
were found.
The source of the oxygen atom in 198 does pose a mechanistic problem. It is either
incorporated during the reaction or during the chromatographic workup. The reaction of
FC2P2S, with 186 and water was attempted in THF. Other than 96 (identified by 3'p-{'H} and
1 H NMR), no other products could be isolated after chromatography. A search of Beilstein,
indicates that no other compounds have appeared in the literature that contain the structural
feature (Figure 6.19).178
162
S S 11 11
\ ---P, /p __ ! / 0 \
\ N N
---\ 11
,/ R S
Figure 6.19 The new structural feature.
As 198 contained two different ferrocenyl environments it was hoped that byelectrochemical
means two different ferrocenyl groups would be detected. The cyclic voltammogram clearly
shows signs of two redox couples occurring (Figure 6.20).
Cl c :~ :0 x o
r---r---r---r---r-~r---r--'---'---'---'---'--~---1~ 1.3 E(V) 1.0 0.8 0.6 0.4 0.2 0.0
Figure 6.20 CV of 198.
A square wave voltammetry experiment confirmed the presence of two different redox
potentia Is and allowed measurement of each (0.658 and 0.776 Volt) (Figure 6.21).
200
o
o 0.2 0.4 0.6 0.8 1 E(V)
Figure 6.21 Square wave voltammetry for 198.
163
Section 6.5
Reactions of Imines with Dithiadiphosphetane Disulfides.
Imines are known to act as dieneophiles in hetero-Diels-Alder reactions and such reactions
have been use in organic synthesis. For instance the formation of alkaloids using intra
molecular Diels-Alder reactions of imines179 The choice of the oxime methyl elher, instead of
the imine in the following example (Scheme 6.15), was likely to have been made due to its
greater stability and lower reactivity. 179
1MS
>' CoCp(CO} 1MS
NDO
11 •
+ ~ MeO ~
1MS MeO
TMS -qP
1
1MS m'tiF •
1MS TMS
Scheme 6.15 SynthesiS by means of an intramolecular hetero-Diels-Alder reaction. 179
As dithiadiphosphetane disulfides take part in cycloaddition chemistry, the reactions of imines
with Fc,P,s. were considered as a route to new nitrogen phosphorus compounds'·' Already
in this work the reaction of N-benzylidene benzyl amine (153) with Fc,P,S. has been shown to
form a mixture of compounds including a 1,3,2.4-thiazadiphosphetane 2.4-disulfide (185) and
a 1,3,2-dithiaphospholane (152). Two further outcomes of such a reaction were identified.
Either a thiazaphosphetane (Equation 6.7a) could be isolated or the P=N containing
intermediate could form other compounds (Equation 6.7b).
s=C p-s • tJ P=N N=C
Equation 6.7b Equation 6.7a
164
The formation of a thiazaphosphetane ring from an imine could provide a new route to these
compounds, avoiding the use of the extremely toxic N-nitroso amines. The reaction of LR with
benzil monoanils has been reported to give 1,3,2-thiazaphospholine-2-sulfides.180 The
mechanism suggested (Scheme 6.16), is surprising. This reaction mechanism requires a
sulfide anion to act as a leaving group and for a three co-ordinate phosphorus cation to act as
a nucleophile.
.. Ph Ph
e~\ / S7U \~ ••• NPh
P==S /(f)
An
! -Sx
Ph Ph
H S ...... .....-NPh
P II \
S An
Scheme 6.16 Literature mechanism for the formation of a 1,3,2-thiazaphospholine-2-
sulfides'8o
Ph S ~ 11.· .NxPh P' JC· -_ ..
An/'" ':::::::S·' S Ph
Ph S I
1I""'-:rN Ph An-P .... 0----
~ Ph
Ph S I \\ N p/ ~Ph
/ 's An :~ CJ Ph
! Ph
S I \\ /N Ph
An-P )(
~---- . C--'s.,..; Ph
Ph An S ~ "ITJ-_Ns:Ph
S_" Y\ "'S Ph
Scheme 6.17 The alternative mechanisms for the formation of the 1,3,2-thiazaphospholine-2-
sulfides.
165
Simple imines formed from aliphatic aldehydes and amines are subject to polymerisation and
hydrolysis. Imines with aromatic groups attached to the nitrogen or the imine carbon, are more
stable and less reactive. Due to the high temperature needed to dissolve the insoluble
dithiadiphosphetane disulfides, it was decided to use these less reactive imines as they were
expected to survive the harsh conditions.
The reaction of dicyclohexylcarbodiimide with Fc,P,S. was performed with the intention of
preparing a pair of thiazaphosphetane rings fused at the carbon to give a spiro system
(Equation 6.8a). It was hoped the steric bulk of the cyclohexyl groups would give steric
protection to the heterocycle. The reaction was carried out and a small yield of an orange
compound was obtained (199), (op 61.0 ppm, m/z 625 amu) (Equation 6.8b}'·9 No molecular
ion was observed by electron impact mass spectrometry for 199, but by the FAB MS method
the molecular ion was observed.
Equation 6.8a Equation 6.8b
'H and 13C-{'H) NMR spectroscopy on 199 revealed the presence of both ferrocenyl and
cyclohexyl groups, in the' H spectrum a complex peak is present at 3.3 ppm. On irradiation of
the alkyl peak at 1.5 ppm, the multiplet (3.3 ppm) (Figure 6.22a) becomes a triplet (Figure
6.22b), showing coupling (3J [3'P-'Hl=19 Hz) of the proton environment to two phosphorus
atoms. The 1 :2:1 triplet would be inconsistent with the spiro compound, but due to the line
widths the triplet could be in reality a doublet of doublets (After cooling to 233K no change was
seen to the 'H NMR spectrum). It is likely that the lines of the triplet are broadened by the
cyclohexyl group switching conformations. The triplet is consistent with the
thiazadiphosphetane structure 199 that was proposed (Equation 6.8b).
166
---~'---I I
3.6 (ppm) 3.4
Figure 6.22a Multiplet at 3.3 ppm
I 2.8
t ) 3.6 (ppm) 3.4
I 3.2
i 3.0
Figure 6.22b Multiplet at 3.3
ppm with irradiation at 1.5
ppm
i 2.8
An attempt was made to react N-benzylidene aniline with Fc,P,S. to form a
thiazaphosphorane (Equation 6.9a). It was hoped that the two phenyl groups would make the
product more stable by means of steric protection and stabilisation by electronic effects. A
solid product was isolated from the reaction, (op 64.2 ppm). NMR and mass spectroscopy
revealed this product to be a thiazadiphosphetane (48) (Equation 6.9b). Examination by X-ray
crystallography revealed the compound to be almost isostructural with 199.'69
5 Ph" 11
N-P-Fc
PhJ-~ -x Not isolated
Equation 6.9a Equation 6.9b
5 5 Fc ~p/ 'p/
Fc/ 'N/ "5 I Ph 48
The molecular structures of 48 and 199 (Figure 6.23 and Table 6.5) revealed the two
ferrocenyl groups to be arranged trans to each other which can be rationalised on steric
grounds. X-ray crystallography confirms the presence of a thiazadiphosphetane ring (Figure
6.23). Compared with Fc,P,S., rotation about the C-P bonds has occurred to increase the
distance from the iron atoms to the endocyclic sulfur/nitrogen atoms in compounds 48 and
199. In the 13C-{'H} NMR spectrum at least five CH, carbon environments were present,
suggesting that in solution the cyclohexyl group is converting between different conformations.
167
c
Figure 6.23 Molecular structure of compound 199. '69
For 199 and 48 the P(1) .. P(1*) separations (2.69/2.67 A) are smaller than that in Fc2P2S.
(3.08 A) and the 8(2) .. N(1) (2.65/2.64 A) distances are smaller than the 8(1) .. 8(1*) distance in
FC2P2S, (2.91 A). These differences are due to the relatively short and strong P-N bonds
pulling the two phosphorus atoms closer to each other. The P(1)-8(2) bond length is shorter
than the mean P-8 bond length in Fc2P2S. (2.18 A), while the P=8 distances are not
significantly different to those in Fc2P2S •. [2.134(3) A].
C7
C26
C16
Figure 6.24 Molecular structure of compound 185.
168
Fe
Fe 81 Figure 6.25 The thiazadiphosphetane ring in compound 185.
169
Table 6.5 Selected bond lengths (A) and angles (0) in the molecular structures of
thiazadiphosphetane disulfides.
199 48 185 200'6'
S(1)-P(1) 1.918(3) 1.917(3) 1.918(4) 1.950(16)
S(2)-P(1 ) 2.095(3) 2.098(3) 2.110(4) 2.121(7)
P(1)-N(1) 1.675(5) 1.704(5) 1.661 (8) 1.689(5)
P(1)-C(1) 1.785(6) 1.789(5) 1.790(9)* 1.818(4)
S(2)-P(2) 2.108(4)
S(3)-P(2) 1.925(4)
P(2)-N(1 ) 1.680(7)
P(2)-C(21 ) 1.781(9)
N(1 )-C(11) 1.44(1 ) 1.40(1 ) 1.47(1 ) 1.517(20)
P(1) .. P(1') 2.67 2.69 2.69' 2.69
N(1 ) .. S(2) 2.64 2.65 2.61 2.65
P( 1 )-S(2)-P(1') 79.0(2) 79.9(2) 79.3(1 )* 79.1 (2)
S(1 )-P(1 )-S(2) 119.9(1) 120.1(1) 119.3(2)
S(1)-P(1)-N(1) 116.7(2) 116.5(2) 117.3(3)
S(1)-P(1)-C(1) 114.1(2) 114.3(3) 114.2(4)*
S(2)-P(1)-N(1) 87.9(2) 87.8(2) 86.8(3) 87.4(3)
S(2)-P(1)-C(1) 105.9(3) 106.6(3) 106.6(3)*
N(1 )-P(1 )-C(1) 109.2(2) 108.4(3) 109.3(5)*
P(1 )-N(1 )-P(1') 105.3(5) 104.5(4) 107.4(5)*
P(1 )-N(1 )-C(11) 127.3(2) 127.7(2) 126.3(6)* 126.8(6)
S(2)-P(2)-S(3) 120.4(2)
S(3)-P(2)-N(1 ) 117.8(3)
S(3)-P(2)-C(21 ) 107.3(4)
S(2)-P(2)-N(1 ) 86.4(3)
S(2)-P(2)-C(21 ) 107.3(4)
S(1 )-P(1 )-C(1 )-C(2) 27.2(7) -13.9(7) -34(1)*
S( 1 )-P(1 )-C(1 )-C(5) 151.2(6) 160.9(6) 141.7(9)'
S(2)-P(2)-C(21 )-C(22) 144.7(8)
S(2)-P(2)-C(21 )-C(25) 31.7(9)
, Numbering scheme for the benzyl compound is different.
170
In 185 the thiazadiphosphetane ring is planar and symmetric (Figures 6.24 and 6.25), with the
sulfurs arranged trans. The benzene ring of the benzyl group is arranged approximately co
planar to a ferrocenyl group. A non-bonded contact [3.59(2) A] exists between C(4) and C(24).
The arrangement of the phenyl group of the benzyl group is such that it is away from the
ferrocenyl groups and sulfur atoms. Also the arrangement of the benzyl is such that the
volume of the molecule in the molecular structure is minimised. The mean P-N distance is not
significantly different to those in other thiazadiphosphetanes. With the exception of the Cop
distance and the phosphorus bound carbon groups, no bond length in the
thiazadiphosphetanes 199 [1.785(6) A] and 48 [1.789(5) A] is different to the distances in
An2P2S3NMe [1.824(3) A] (Figure 6.26).'8' The CoN bond length [1.517(20) A] in An2P2S3NMe
is longer than the distance in 48 [1.40(1) A].
S S Fc \\ / , I
P P I 'N/ \\
Fc I S Me
Figure 6.26 Structure of An2P2S3NMe (200).
The formation of 199 can be rationalised by the following mechanism (Scheme 6.18).
Step 1 Step 2 Step 3 S
II Fc-P
S DCC S S \\ S S Fc
II 11 II S \\ / , I Fc-P • Fc-P-NCy • Fc-P • P P
[2+2] [2+2] \\ I~ -CyNCS \\ I 'N/ \\ S
S ~ NCy Fc I S
NCy
Scheme 6.18 Mechanism for the formation of 199.
1. The ferrocenyl dithiophosphine ylide reacts with a molecule of DCC to give a
thiazaphosphetane.
2. The thiazaphosphorine then decomposes to cyclohexyl isothiocyanate and a
thioimidophosphine ylide.
3. The thioimidophosphine ylide reacts with a dithiophosphine ylide to give the
thiazadiphosphetane product.
Cy
171
In the above reaction it is likely that the formation of the thioiminophosphine ylide is a slow
process, and the dithiophosphine ylide will be present in the mixture in greater concentrations.
The dithiophosphine ylide will be able to trap the thioiminophosphine ylide to give the
thiazadiphosphetane disulfide. An alternative first step would be attack of the imine as a
nucleophile on the dithiophosphine ylide followed by a ring closure to give the
thiazaphosphetane.
The reaction of LR with DCC was carried out on a large scale. After recrystallization of the
thiazadiphosphetane (201) 162 the mother liquor was distilled to give a good yield of cyclohexyl
isothiocyanate (Equation 6.10). The isolation of the cyclohexyl isothiocyanate (Identified by IR,
GCMS and NMR spectroscopy) provides further evidence for the above mechanism.
S S An \\ / , I P P
/ 'S/ \\ An S
S S An \\ / , I P P +
/ 'N/ \\ An I S
Cy
Equation 6. 10
Other synthesis routes for the thiazadiphosphetane sulfides are outlined in Scheme 6.19. 157,162,164.181
S S An \\ / , /
P P / 'S/ \\
An S
PhNCO
R may be methyl or anisyl
S S R' \\ / , / P P
/ 'N/ \\ R' S
I R
PhNCS ..
R' may be methyl, phenyl or trimethylsilyl
i Me3SiNMeSiMe3
S S An \\ / , /
P P / 'S/ \\
An S
S S An \\ / , /
P P / 'S/ \\
An S
Scheme 6.19 Different routes to thiazadiphosphetane disulfides. 172
A related ring was prepared by the reaction of dichlorophosphine sulfides with primary
amines'82 It is likely that the thioiminophosphine ylide is formed, but as the dithiophosphine
ylide is absent from the reaction mixture the formation of the thiazadiphosphetane ring is
avoided and the diazadiphosphetane disulfide is formed. A mechanism that explains the
formation of the different products is shown below (Scheme 6.20).
S 11 P-CI
R/ 'Cl
S
-HCI
11 R'NH2 P .... 1----
R/ \ ....... NHR' NHR'
l-HCI
[2+2] • Dimerise
R'
S ~ R \\ / , I P P
I 'N/ \\ R 1 S
R'
Scheme 6.20 Synthesis of diazadiphosphetane disulfides and thiophosphonyl diamides.
Another synthesis of a diazadiphosphetane disulfide is by the reaction of NpP,S. with HMDS
followed by sublimation of the products (Equation 6.11 ).'83
'-'::::
1. HN(SiMe3h ~ ..-::; • SiMe
2. Sublime N i p/ ....... p
S-:::::- ....... W .... .::::.S
Equation 6.11
SiMe 3
The reaction of Fc,P,S. and N-benzylidene 2,4-dimethylaniline gave, after purification, the
thiazadiphosphetane (202) (Scheme 6.21). This compound was made to investigate the
effects of increasing the steric crowding around the nitrogen atom. This compound might have
the phenyl group tilted to increase the distance between the ortho methyl and the atoms
bonded to the phosphorus atoms.
It was postulated that rotation around the CoN bond of the thiazadiphosphetanes could occur.
Of the two 'H NMR resonances due to methyl groups in 202, one is broader than the other.
On cooling the solution to 233K this resonance remains unchanged suggesting that either the
rotation is still occurring or alternatively the rotation was never occurring. If the phenyl group
was rotating rapidly then the methyl ortho to the nitrogen would be in a variety of different
173
environments and an average of these will be seen in the NMR. The methyl group para to the
nitrogen will not be moved in space by.a rotation of the C-N bond so it will remain in a single
environment hence it is not subject to the same broadening effects as the other methyl could
be. The reactions of N-benzylidene 2,6-dimethylaniline and N-benzylidene 1-phenylethylamine
with Fc.P.S. were attempted, but these reactions gave intractable mixtures from which no
pure product could be isolated (Scheme 6.21). However, the reaction of 2,6-dimethylaniline
with Fc.P.S. gave the thiazadiphosphetane (203) in low yield (Scheme 6.21). The formation of
this product does offer a new route to these heterocycles. The outcome of this reaction is
different to the reaction of LR with aniline. This latter reaction forms a
phosphonothioicdiamide 163 due to the differences in steric bulk around the nitrogen of the
amine.
As imines react with Fc.P.S. to form thiazadiphosphetane disulfides, the reaction of N-phenyl
triphenylphosphine imine with Fc.P.S. was attempted. While a good yield of
triphenylphosphine sulfide was obtained, no other phosphorus compounds could be isolated
from the intractable mixture of P-ferrocenyl compounds (Scheme 6.21).
Intractable PhN=PPh3 mixture
R can be 2,6-dimethylphenyl or 1-phenylethyl l~
Ph~N,©
•
Scheme 6.21 Formation of thiazadiphosphetane disulfides.
48
174
Little variation was seen in the phosphorus NMR chemical shift, the u(P=S) stretching
frequency or the redox potential for the different thiazadiphosphetane disulfides (Table 6.6)
Table 6.6 Selected spectroscopic and electrochemical data for thiazadiphosphetanes
Compound I5p (ppm) u(P=S) (cm") E'/2N
48 (Fc,P2S3NPh) 64.2 690 0.77
185 (FC,P2S3NBn) 65.1 681 0.80
199 (FC,P2S3NCy) 61.0 679 0.74
201 (An2P2S3NCy) 60.2 697 a
202 [Fc2P2S3N(2.4-dimethylphenyl)] 66.9 687 0.78
203 [Fc2P2S3N(2,6-dimethylphenyl)] 63.9 683 0.78
a. Measurement not attempted.
Section 6.6
Electrochemical Characterisation of the Thiazadiphosphetane Disulfides
using Square Wave Voltammetry.
The diferrocenyl thiazadiphosphetane disulfides have similar cyclic voltammograms, all
exhibiting reversible couples with strong prepeaks (Figure 6.27). This contrasts with the cyclic
voltammogram recorded for bis-(dimethylferrocenyl) dithiadiphosphetane disulfide (12), where
a single couple without prepeaks was observed.
Cl c
·13
'" '0 ~---....Jcu
~~.a:: 0.0
Cl c
0.6 0.4 0.2
Figure 6.27 CV for 185.
·N 15 'x o
0.0
175
Using normal cyclic voltammetry the sequential oxidation of the ferrocenes could not be
clearly seen. In nonmal cyclic voltammetry the current flowing due to electrochemical events
has superimposed on it a current due to capacitance. Square wave voltammetry offers greater
resolution, as only the faradaic current is recorded. For example, a single peak at 0.426 V was
observed for the oxidation of ferrocene by the square wave method instead of a curve like that
seen in CV (Figure 6.28).
4
o ~ ----------- ----------------o 0.2 0.4 0.6 0.8
E(V)
Figure 6.28 Square wave voltammetry trace for ferrocene.
All of the diferrocenyl thiazadiphosphetane disulfides that were examined by the square wave
method showed two peaks suggesting sequential oxidation of the ferrocene groups. These
results are summarised in table 7.8. An example of one of the traces is shown below (Figure
6.29). The peaks are at 0.711 and 0.801 Volt. Under identical conditions the redox couple was
observed at 0.766 volt by CV.
"~~.4~----~0~.5-------0~.~6-----0~.-7------0~.-8-------0.~9------~------l E(V)
Figure 6.29 Sq~are wave voltammetry trace for 185.
Table 7.8 Results from the square wave experiments on the thiazadiphosphetane disulfides.
Compound N-R group llE
48 Ph 70mV
185 Bn 88mV
199 Cy 64mV
202 2,4-Me2C.H3 90mV
203 2,6-Me2C•H3 66mV
176
In compounds which contain more than one ferrocenyl group, an interaction between the two
ferrocenyl groups could occur (Scheme 6.22). After the first ferrocene is oxidised to
ferricenium, it could have an electronic effect on the second ferrocene. If two redox couples
were observed then the difference is recorded in the <lE column of Table 7.8, 7.9. A strong
interaction has been observed for biferrocene.,'92.1.3 On adding spacer groups this interaction
becomes weaker'·2.1.3.1 .. ,l.5,l96 As the data in table 7,9 was obtained using CV and DC
polarography, weak interactions between the ferrocene centres could have been
unobservable.
1\ Fe Fe
207 204 Fe-Fe
208 209 210 211
Fe Fe Fe
'j=\Fe
0 Fe~Fe Q Fe S 215
Fe 213 214
212
[)=<Fe
Fe
Ph Fe
>=< Ph Fe 216 217
219
220 Scheme 6.22 Compounds with more than one ferrocenyl group.
177
Table 7.9 Electrochemical data for polyferrocenes.
Compound E\ (volt) dE (mV) Reference
204 0.13/0.72 590 192
205 0.31/0.64 330 192.193
206 0.39/0.56 170 192
207 0.33/0.37 40 192
208 0.01/0.16" 170 195
209 0.02" 195
210 0.02" 195
211 -0.02" 195
212 0.06" 195
213 -0.02/0.13" 150 195
214 0.0110.15" 140 195
215 -0.10/0.06" 160 196
216 -0.09/0.05" 160 196
217 -0.05/0.10" 150 196
218 0.0310.19" 160 196
219 0.59 194
220 0.60 194
a. Relative to the ferrocene/ferricenium couple.
The communication between two ferrocenyl groups is possible through four a-bonds, but not
when the phosphorus atoms are not linked via a nitrogen atom. These results are similar to
3'P-{'H} for 221.'83 The 'J(31 p _31 p) coupling in 221 is greater (18 Hz) than the coupling
constant observed for MeONpP,S. (7 Hz) (Scheme 6.23).'83 The shape of the
thiazadiphosphetane ring in 221 is likely to be similar to that in NpP,S., rather than that in
Fc,P,S. , 48, 185 and 203.
OMe OMe
Scheme 6.23 MeONpP,S. and 221.
178
Section 6.7
The Reaction of Heptamethyl DisilazanelTHF with Diferrocenyl
Dithiadiphosphetane Disulfide.
The reactions of heptamethyl and hexamethyl disilazane with LR (Equation 6.12a),'82 NpP,S.
(Equation 6.12b),'84 MeONpP,S.'8' have been reported to give thiazadiphosphetane
disulfides.
S S An \'V "p' / "S/ \\
An S
S S An Me3SiNMeSiMe3 \\ / " / .----l.... P P
Ll. / "N/ \\ An I S
Equation 6.12a
Me
Equation 6.12b
The reaction of Fc,P,S. with heptamethyldisilazane in dichloromethane was attempted. The
reaction mixture gave a mixture of products including traces of a malodorous substance,
thought to be bis-(trimethylsilyl) sulfide, which could not be removed. The experiment was
repeated using THF in place of the dichloromethane, after chromatography and removal of
solvent a heavy red oil (222) (op 82.7 ppm) was obtained. Compound 222 is a 1: 1: 1 adduct of
P-ferrocenyl dithiophosphine ylide, THF and heptamethyl disilazane (Equation 6.13).
o Me3SiNMeSiMe3 ..
222
Equation 6. 13
179
This reaction is similar to the reaction of P-organo trithiophosphonic acid S, S'-trimethylsilyl
ester with THF to form P-organo trithiophosphonic acid S,S'-bis-(4-trimethylsiloxybutyl) esters
(Equation 6.14).'90
S 11 THF
R-P-SSiMe3 • I Room temperture SSiMe3
Equation 6. 14
R can be methyl ot tert-butyl
Compound 222 could be formed from a S-trimethylsilyl compound that would formed from
FC2P2S, and heptamethyl disilazane (Scheme 6.23) .
•
THF 224 .... 1----
Scheme 6,23 Formation of 222 from FC2P2S./ THF / Me3SiNMeSiMe3'
The reaction forming 222 is similar to the ring opening of small and medium sized cyclic ethers
with triphenyl phosphine and strong acids (Equation 6.15).'9' In the formation of 222 the
BrfIlnsted acid has been replaced by the oxophilic silicon while the sulfur replaces the
phosphorus.
n=1,2 or 3 Equation 6.15
Unlike most reactions of substituted epoxides with nucleophiles under acidic conditions, the
nucleophile attacks the less substituted carbon. In this unusual reaction steric effects are likely
to be dominate over the electronic effects, thus favouring attack of the nucleophile at the more
substituted carbon. (Scheme 6.24).
180
Basic conditions
Attack at least hindered carbon.
H
~ H+ D
AcidiC· R~I conditions R
/
H I o
R+~ R
Small contribution
~b R~
R
NuH
Large contribution
H I
Nu 0 R--r R
Scheme 6.24 Expected mechanisms of ring opening of an epoxide under basic and acidic
conditions.
Section 6.S
The Reactions of Substituted Ureas with Diferrocenyl
Dithiadiphosphetane Disulfides
The reaction of 1,3-diphenylurea (117) with LR was reported to give ArP(S)(NHPh)" '6' using
Fc,P,S. this reaction was reinvestigated. Besides the diamide (49) (op 54.5 ppm) a
thiazadiphosphetane (48) was obtained.
Close examination of the infra red spectrum of FcP(S)(NHPh), (49) revealed the presence of
two different NH stretches (Figure 6.30). One is sharp [u(NH) 3382 cm"] while the other
[u(NH) 3242 cm"] is broader suggesting that in the solid some NH groups are involved in
hydrogen bonding (Figure 6.31).
)0.9 JO
" 26
20
%T 18
16
14
12
iO }J11.9
]1'1.0
S.2 ±:-:-_-.,..:-:-__ ----::=-___ = ___ --:,--__ -::-:..,... __ --,~__:-3926.2 JlOO 3600 3400 3200 3000 2800 2693.7
=-1
Figure 6.30 Infra-red spectrum of 49.
181
Free NH
/
Figure 6.31 Hydrogen bonding network in 49.
X-ray crystallography reveals (Figure 6.32 and Table 6.9) that in the solid state 49 forms
hydrogen bonded dimers, using an amine proton of one molecule and the thiophosphonyl
group of another.
. Figure 6.32 Molecular structure of compound 49.
182
Table 6.9 Selected bond lengths (A) and angles (0) found in the molecular structure of 49.
S(1)-P(1) 1.941 (2) S(1)-P(1)-N(11) 117.0(2)
P(1)-N(11) 1.662(4) S(1)-P(1)-N(17) 108.1(1)
P(1 )-N(17) 1.649(4) S(1)-P(1)-C(1) 112.6(2)
P(1 )-C(1) 1.779(5) N(11 )-P(1 )-N( 17) 106.4(2)
N(17)-S(1*) 3.416(4) N(11)-P(1)-C(1) 99.6(2)
S .... H 2.54 N(17)-P(1 )-C(1) 113.0(2)
P(1 )-N(11 )-C(11) 127.2(3)
P(1 )-N(17)-C(17) 130.7(3)
P(1)-N(11)-H(11) 134.8
P(1 )-N(17)-H(17) 110.6
The P-N bond lengths are not significantly different from each other or the P-N bond lengths in
94 [1.648(4) and 1.664(4) A] or those in 185 [1.661(8) A] and 199 [1.675(5) and 1.680(7) A]
but are intermediate between P(1)-N(11) [1.700(5) A] and P(1)-N(1) [1.631(4) A] in 95. The P
N distances are shorter than P(1 )-N(1) [1.704(5) A] in 48. These differences are consistent
with the bonding being affected by the electronic effects of nitrogen groups (Figure 6.33).
Electron donating strength
NMe2 > NHPh > N(P)Ph > NCS
Figure 6.33 Comparison of electronic properties of nitrogen groups.
The mechanism by which 1,3-diphenyl urea (117) and Fc,P,S. form 49 is not clear.
Conversion of 117 to the thiourea, followed by loss of hydrogen sulfide would give N,N'
diphenyl carbodiimide. The reaction of the carbodiimide with Fc,P,S. could be a reasonable
route to 48 (Scheme 6.25).
o Ph, )l /Ph
N N I I H H FC2P2S41-PhNCS
S S Fc ~p/ "p/
Fc/ "N/ ~S I Ph
Scheme 6.25 A possible mechanism for the formation of 48.
183
In the formation of 49 from 117 both carbon nitrogen bond cleavage and nitrogen phosphorus
bond formation are required. One possible mechanism would require the reversible
dissociation of N,N'-diphenyl urea (or N,N'·diphenyl thiourea) to phenyl isocyanate (or phenyl
isothiocyanate) and aniline. Both the aniline and the isocyanate could then take part in
reactions. It is likely that when 117 and Fc,P,S. are heated together in xylene, that more than
one reaction could be occurring at the same time. Other phosphorus sulfide diamides can be
prepared by the reaction of dichlorophosphine sulfides with primary or secondary amines.'83
In the CV of 49 indications of an oxidation were seen (E"2 greater than 1.3 Volt), as anilines
can electropolymerise, the compound was subject to many cycles rather than one'S'.'93 The
cyclic voltammetry indicated that the platinum electrode was becoming coated with a poorly
conductive film (Both in the presence and absence of camphor sulfonic acid), as the current
due to the redox couple steadily decreased to a very low value. On visual examination of the
platinum wire, it was found to have acquired a dull coating that could be removed by
electrochemical cleaning.
To further examine the reactions of ureas with Fc,P,S., N,N'·dimethyl·N,N'·diphenyl urea and
N·methyl·N,N'-diphenyl urea were reacted with Fc,P,S •. No nitrogen phosphorus compounds
were isolated from these reactions, but instead a FcPOS trimer was isolated (96) (Equation
6.16). 96 is a likely phosphorus·oxygen containing side product formed in thionation reactions.
This outcome is consistent with the hypothesis of the carbodiimide being required as an
intermediate. The presence of even one methyl group will prevent the formation of any
diphenylcarbodiimide, also their presence will make the thionation of the urea more likely by
slightly increasing the electron density of the carbonyl oxygen.
S S Fc
\'1'/ "F'" Fe! "S/ \'5
(PhNMe)2CO or
PhNMeCONHPh .. S Fc
FC __ ~/O,-F"'-;::::::S
6 6 Equation 6.16
'-p/
,jI 'Fc
96
The 31 p-{'H} spectrum of 96 appears (on first sight) to be an AMN system in which no coupling
between the M and N environments is observed (Figure 6.34). However simulation with
geNMR suggests the spectrum to be an AB, system with second order effects exerting a
strong influence (Table 6.10).
184
Table 6.10 Interpretation of the phosphorus NMR spectrum of 96 using geNMR.
Phosphorus environment
I 77
Op (ppm)
76.59
74.48
I 76
I 75
v'-
Figure 6.34 31p-{'HJ NMR spectrum of 96.
I 74
49
49
The 3'P-{'HJ NMR spectrum of 96 contrasts with the single environment (op 72 pp m) reported
for 2,4,6-tris(para-methoxyphenyl)-1 ,3,5,2,4,6-trioxatriphosphinane 2,4,6-trisulfide '04 (Figure
6.35), which has been found by X-ray crystaiiography to have two aromatic groups on one
side of the ring, with the third on the other side. For such a compound an AX, system could be
expected in the 31 p -{'HJ NMR spectrum, but second order effects could distort the spectrum to
cause to appear as a singlet. Alternatively the molecule could be flipping from one
conformation to another so making the peaks broad.
185
S An ,/
p 0/ '0 I I
S,,,,,,p P"""S An' '0/ "An
Figure 6.35 Structure of An3p,03S3'
'H NMR spectroscopy upon 96 reveals two ferrocenyl groups in a 1:2 intensity ratio (OH 4.25
and 4.25 ) (Table 6.11) suggesting that the isolated compound is one of two isomers (Scheme
6.26).
Table 6.11 'H NMR spectroscopic data for 96.
OH (ppm) multiplicity Integration height
4.25 s 10H
4.35 s 5H
4.40 m 2H
4.47 m 2H
4.54 m 2H
4.60 m 2H
4.85 m 2H
4.96 m 2H
Scheme 6.26 The two conformations possible for 96.
The conformation on the left is likely to have a lower energy because fewer bulky ferrocenyl
groups are in the axial positions.
The CV of 96 showed signs of more than one redox couple, suggesting communication
between the ferrocenyl groups via the a-bonds of the phosphorus heterocycle. This was
confirmed by a square wave voltammetry experiment. Although the different redox couples
can not be perfectly resolved, it is clear that more than one redox couple is present (Figure
6.36).
186
o
0.4 0.5 0.6 0.7 0.8 E(V)
0.9
Figure 6.36 Square wave voltammetry experiment for 96.
Section 6.9. Experimental
Synthesis of 94
1 .1
To Fc,P,S. (1.079g. 1.93 mmol) was added 184 (0.7 ml). After stirring to mix the reactants no
reaction was seen to occur. Within a minute of the reaction mix1ure being heated in a 140°C oil
bath a violent reaction was observed. The tube was withdrawn from the oil bath and allowed to
cool, before being replaced in the oil bath for 4 minutes. The reaction mixture was then
allowed to cool to room temperature, before the reaction products were recrystallized from a
small volume of toluene to give a brown product (1.385 g). This solid was examined by 31 p
NMR spectroscopy and was found to contain paramagnetic material. Chromatography on
silica followed by removal of the solvent gave 94 as an orange-yellow solid (0.924g. 2.2 mmol.
57 %), By cooling a hot toluene solution crystals were obtained. m.p. 150°C d. (Found: C,
45.5;H, 4.8; N, 13.1. C,sH"FeN.PS, requires C, 45.7; H, 5.0; N, 13.3%). IR 2927m, 1618s,
1547s, 1442m, 1358m, 1253m, 1190m, 1180m, 1105m, 1055w, 1022m, 997w, 954s, 937m,
861s, 847m, 821m, 680s, 641m, 575m, 510m, 492w, 473m, 417w, and 330w (cm-'). op 61.82
ppm. OH (ppm) 4.46 (m) and 4.28 (m) ppm (9 H in total), and 3.02 ppm (12 H). Oc (ppm) 154.7
(Quat), 80.7 [d 'J(31 p_13C) 168 Hz, quat]. 71.6 [d J(PC) 14.9 Hz]. 70.5 [d J(PC) 12.7 Hz], 70.1,
and 37.3 ppm. MS(EI+) m/z 420 (M+), 280 (FcPS,)+, 248 (FcPS)+, 217 (FcS)+, 184, 121,69,
51 and 31. CV, A reversible redox couple was observed at 0.56 volt.
Low temperature synthesis of 94
Fc,P,S. (0.494g. 0.882 mmol) was suspended in toluene (10 ml). To this was added 184 (0.5
ml. 0.43g. 6.2 mmol), and the mix1ure was slowly brought up to reflux temperature. After 8
minutes almost all the Fc,P,S. was absent (TLC). This mix1ure was allowed to cool to room
temperature and stand for 3 days. Flash column chromatography gave a red oil (0.144g. 0.411
mmol. 23 %) (95) and 94 as a yellow solid (0.449 g. 1.07 mmol. 61 %). 94 made in this
reaction was identical to that made at a higher temperature. The red oil was examined by 31 p
NMR spectroscopy and found to be almost entirely a single phosphorus compound. 95 (120
187
mg) was heated under reflux in xylene for three hours, during which time the mixture became
very dark and cloudy. A black solid formed in the mixture, after filtration through a short pad of
AI20 3 a pale orange solution was obtained, after removal of the solvent an orange oil remained
(24 mg). This by 31p NMR spectroscopy was almost pure 95. op 67.8 ppm with minor peaks at
58.5 and 53.7 ppm. OH (ppm) 4.67,4.56,4.50,4.70,4.41, Minor singlets at 3.08 and 3.06 ppm
combined integration of 0.228. 2.70 (d) integration of 1.000.
The reaction of Fc.P.5. and 184 was repeated on a larger scale (2.91g. 10.4 mmol) Fc.P.5.
and 184 (1.7 ml. 1.5g. 21 mmol) in toluene (50 ml), the reaction mixture was allowed to cool
before the addition of petroleum ether (40 ml) to remove 94 as a precipitate. After filtration and
removal of solvent a red oil remained. This oil was purified by flash column chromatography
(petroleum ether/toluene 75:25) to give 95 as a red oil (0.57 g, 1.6 mmol, 15 %) which
crystallised on standing. (Found: C, 44.9; H, 4.1; N, 8.1. C'3H'5N,FePS, requires C, 44.6; H,
4.3; N, 8.0%). IR 3098m, 2997w, 2941s, 2885s, 2845m, 2805m, 2553w, 2031vs, 1649m,
1455m, 1413m, 1388w, 1368w, 1351w, 1309m, 1279s, 1183s, 1107m, 1059m, 1029s,
1001sh, 977s, 897w, 823s, 743s, 671s, 627m, 556m, 494s, 478s and 448s (cm-'). op 67 ppm.
OH (ppm), 4.6 (m), 4.4 (m), 4.3 (s). Total integration of signals between 4 and 5 ppm is 9 H. 2.6
[6H, d 3J(31 p_'H)=14 Hz]. Oc (ppm) 144.4 (quat), 75.4 [d 'J(3'P_13C)=91 Hz, quatJ, 72.0 [d
'J("P-13C)=21 HzJ, 71.2 to 70.3 (m), 69.9 (s) and 36.3 (s). MS(FAB) mlz 373(minor), 350(M\
318(M -st, 306, 292(M -NCSt, 285,274,260,248, 186, 165, 128, 121, and 108. MS(EI+)
mlz 350(M+), 348, 318 (M -st, 306, 292, 285, 274, 260, 248, 217, 186, 171, 128, 121, 108,
96, 75, 60 and 44. Molecular ion found at 349.9767 amu ("C,,'H'514N,56Fe3'p32S, requires
349.97633 amu (1.1 ppm error). CV, a reversible redox couple was observed at 0.74 volt.
The treatment of 95 with water in THF.
95 (1.24 g) was dissolved in a mixture of THF (20 ml) and water (5 ml). This mixture was
allowed to stand for 34 days without significant change observable by TLC. After the addition
of a drop of sulfuric acid the mixture was allowed to stand again for 7 days without significant
change. From this mixture the 95 was isolated in 88 % recovery by the removal of the THF in
vacuum followed by addition of ether and drying with MgSO. before evaporation to give pure
95.
The treatment of 95 with excess of isopropyl amine.
To 95 (351 mg. 1 mmol) in THF (15 ml) was added isopropyl amine (7 ml. 4.9 g. 82 mmol).
This mixture was allowed to stand overnight before the removal of all volatile compounds. TLC
indicated the absence of 95. After dissolving the residue in ether (28 ml) followed by washing
with water (12 ml) the ether extract was dried with MgS04 , after filtration and evaporation a
red solid was obtained. This was applied to a flash column (elution with CH,CI, followed by
188
EtOAc 25% in CH,CI,) after evaporation a red solid was obtained. Further flash column
chromatography on the solid (elution with 40% CH,CI, in petroleum ether, then CH,CI,
followed by 20% EtOAc on CH,CI,), followed by evaporation, gave 191 as an orange solid
(0.324 g. 0.69 mmol. 69 %). IR 3396m, 3263m, 2194w, 3150sh, 3089w, 3037w, 2981sh,
29675, 2930m, 2864m, 2824w, 2784w, 16135, 15365, 1471m, 1435m, 1413w, 1388m, 1367m,
1342m, 1312w, 1294w, 1260w, 1080m, 1170m, 1140w, 1120w, 1106w, 1049w, 1023m,
1001w, 971sh, 959m, SOOw, 872w, 852w, 823m, 814w, 774m, 720w, 700m, 637m, 611m,
570w, 492m, 464w, 44Ow, and 339w (cm-'). op, 61.6 ppm. OH (ppm) 4.66 (1 H, m), 4.44 (1 H,
m), 4.30 (2 H, m), 4.25 (5 H, 5), 3.9 (2 H, br), 2.45 16H, d(14 Hz)], 1.28 (13 H, m). MS(ES+)
435,436, 869, 870, and 891. MS(ES-) 433 and 434.
The treatment of 95 with an excess of methanol in the presence of triethyl amine.
To 95 (1.08 g. 3.09 mmol) was added triethyl amine (10 ml. 7.3 g. 72 mmol), methanol (10 ml
7.9 g. 247 mmol) and THF (12 ml) and the resulting mixture was allowed to stand overnight
before the removal of all volatile compounds. TLC indicated the absence of 95. After the
addition of ether (100 ml), and water (25 ml) the mixture was transferred to a separating funnel
and the water layer was removed. The ether extract was washed with water (50 ml) three
times, before being dried with MgSO •. After filtration, removal of solvent gave a brown tar-like
material. This was found to be an intractable mixture by TLC and mass spectrometry.
The reaction of FC2P2S, and 186.
To 186 (2.0 ml. 1.9g. 17.5 mmol) was added to Fc,P2S, (2.45g. 4.38 mmol) to give a red
mud-like mass, to this was added a little toluene and this mixture was heated in a hot bath
(110°C) for 2 minutes. After cooling, petroleum ether was added and the tube was shaken.
This reaction mixture was seen to thicken before crystallisation to give a red solid. This red
solid was recrystallized from toluene (12 ml) to give an orange solid 187 (2.42g. 4.84 mmol. 55
%) and a red tar. The recrystallized 187 retained a trace of toluene, detected by 'H NMR
spectroscopy, even after prolonged drying in high vacuum so a sample of 187 was dissolved
in a little COCI3 before removal of all solvent in high vacuum to give a sample for examination
by 'H NMR spectrscopy. m.p. 160°C d. (Found: C, 52.8; H, 5.8; N, 11.0; S, 12.8.
C"H29N.FePS, requires C, 52.8; H, 5.8; N, 11.2; S, 12.8%). IR (Nujol mUll) 3092m, 15995,
15325, 1495m, 14645, 14475, 1413m, 1399m, 1378m, 1365m, 1351m, 1318w, 1285w, 12405,
12085, 1186m, 1178m, 11235, 1106m, 1081w, 1062w, 10205, 10025, 9945, 9485, 9385, 8845,
8525, 836m, 8065, 795m, 7285, 694m, 6745, 6455, 6215, 589m, 540w, 502m, 486m, 464w,
455w, 421w, 409m, 380w, 349w, 326w (cm-'). op 61.6 ppm. OH (ppm), 4.5 (2 H, m), 4.33 (7 H,
5),3.70 (8.7 H, t, 5.1 Hz), 1.6 (13.6H, m). Oc (ppm), 71.5 (d, 15 Hz), 70.4 (d, 12 Hz), 70.0, 46.3
(CH,), 25.7 (CH,), and 24.6 (CH,). CV, Two redox couples were observed, one at 0.53 volt
189
and another at 0.87 volt. The second redox couple shows signs of slow electron transfer
(redox couple measured at 200 mV s").
The red tar was subject to flash column chromatography on silica (24 g, hexane/CH2CI2 then
CH2CI2 then EtOAc) to give three different orange fractions. The first fraction after removal of
solvent fumished P-ferrocenyl P-(l-piperidinyl) thiophospho isothiocyanate (189) is a red oil
(0.63 g. 1.6 mmol. 18 %), this was pure by GCMS. (Found C, 48.8; H, 4.9; N, 7.3; S, 16.5.
C,sH,.N2FePS2 requires C, 49.3; H, 4.9; N, 7.2; S, 16.4). IR 3098m, 29365, 2852s, 2022vs,
1463m, 1450m, 1442m, 1413m, 1387w, 1369m, 1335m, 1311w, 1278m, 1259w, 1205s,
1184s, 1160s, 1107s, 1066s, 1027s, 1003m, 952s, 896w, 850m, 825s, 730s, 678s, 628m,
559m, 491s, 477s, and 446s (cm"). op (ppm), 63.3. OH (ppm), 4.65 (m), 4.55 (m), 4.49 (m),
4.40 (s). Integration for 4.7 to 4.3 ppm (9 H), 3.2 (7 H, m), 1.5 (11 H, m). When the peak at 1.5
ppm is irradiated in a double irradiation experiment the peak at 3.2 ppm changes to a pair of
doublets of doublets. 2J['H-'Hj=12.6 Hz. 3J['H_3 'Pj=10.2 Hz for the peak centred at 3.2 ppm.
3J['HY'Pj=9.8 Hz for the peak centred at 3.1 ppm. Oc (ppm), 145.0 [d J(PC) 2.5 Hzj, 75.8 [d
J(PC) 162 Hzj, 72.9 to 71.4 (m), 70.9 (s), 46.1, 25.9, 25.8, and 24.4. CV, A reversible redox
couple was observed at 0.72 volts. MS(EI+) mlz 390, 332, 307, 274, 248, 186, 146, 121, and
84. Molecular ion found at 390.0074 amu (12C,.'H,.Fe'4N231p32S2 requires 390.0076 amu
error of 0.7 ppm). The second fraction was an intractable mixture, while the third fraction was
187 (454 mg. 0.91 mmol. 10%).
General method for the reactions of dithiadiphosphetane disulfides with piperazine 1, 4-dinitrile.
Synthesis of 192.
A hot solution of LR* (0.898 g. 1.74 mmol) in toluene (11 ml) was rapidly added to a hot
solution of piperazine l.4-dinitrile (0.46 g. 3.38 mmol) in acetonitrile (13 ml). This mixture was
heated under reflux (30 to 50 minutes). After cooling, if the mixture was cloudily it was filtered
before the solvents were removed in vacuum to give the resin (192). When a solution of 192 in
chloroform was allowed to evaporate a transparent glassy film was formed. Alternatively the
solution of piperazine-l,4-dinitrile can be added to the solution of the dithiadiphosphetane
disulfide. ). IR (thin film) 2960s, 2217s, 1977vs, 1614vs, 1529s, 1488s (cm''), op (ppm): 61.7,
59.3 and 41.0. OH (ppm): 7.7 (2.0 H, br m), 7.0 (1.0 H, br m), 3.9 (5.6 H, br m), 3.3 (4.6 H, br
s), and 1.4 (9.0 H, br s). MS(ES-) mlz 642, 469, 427, 384, 267, 347, 289m 285, 273, 259, and
243. MS(ES+) m/z 1048, 823, 789, 694, 653, 594, 565, 531,464,440,429, and 412.
Synthesis of mixture 196
A mixture of Fc.P.S. (0.311 mg. 0.56 mmol) and LR* (1.469 g. 2.85 mmol) was reacted with
piperazine l,4-dicarbonitrile (0.93 g. 6.83 mmol) using the above method. This gave 196 as an
190
orange solid (2.53 g). IR 29595, 22165, 1976vs, 1612vs, 1534vs, 1488m, 1443m, 1394m,
1362m, 12605, 1199m, 11335, 1093m, 1024m, 995m, 948m, 9095, 821m, 7335, 682m, and
644m (cm-'). op (ppm) 61.7 and 59.3. OH (ppm) 7.8 (2.0 H, br m), 7.0 (1.0 H, br m), 5 (1.3 H, br
m), 3.9 (7.9 H, br m), 3.2 (4.8 H, br m), 1.4 (9 H, br 5). MS(ES+) m/z 1069, 1047, 947, 811,
789,594,553,531, and 417.
The reaction of piperazine 1,4-dicarbonitri/e and FC2P2S, to furnish 197.
Fc2P2S, (2.23 g. 3.98 mmol) in toluene (20 ml) and piperazine 1,4-dinitrile (1.1 g. 8.08 mmol)
in acetonitrile (11 ml) were reacted using the general method to give a red resin. This was
dissolved in THF (20 ml) and the resulting solution was added to well-stirred petroleum ether
to give 197 as an orange powder (1.56 g). (Found: C, 44.5(44.4); H, 3.8(3.8); N, 14.0(13.8).
The infinite polymer would require C, 46.2; H, 4.1; N, 13.5 %). Duplicate results in brackets. IR
3099m, 3088m, 3036w, 2976w, 2917m, 2857m, 2216vs, 1976vs, 16155, 15345, 1497m,
1446m, 1413m, 1387m, 1365m, 1313w, 1275m, 11865, 1128m, 1108m, 1049w, 1027m,
997m, 954m, 907m, 8245, 7315, 6805, 643w, 628w, 576w, 522w, 494m, 480m, 414w, and
392w (cm-'). op 63.8 ppm with a minor peak at 62.3 ppm. MS(ES+) rnlz 1113, 850, 833, 696,
638, 591, 553 and many peaks below 460. CV, (Thin film platinum wire dipping into 0.2M
Bu.NCIO. in MeCN) almost reversible redox couple exhibiting slow electron transfer, Redox
potential of 0.77 volt (measured at 200 mVs-'). The film showed strong electrochromism.
When in the reduced form it was pale orange while when oxidised it was green/black. These
electrochemical results were duplicated using a glassy carbon electrode modified with a
coating of 197, the presence of lead (11) perchlorate (2.5 mmol in a 0.2 M Bu.NCIO. solution in
MeCN) did not change the electrochemical behaviour of the electrode. When the nonaqueous
supporting electrolyte was substituted for 0.2 M KN03 in water, the electrode coating
degraded after a few cycles. m.p. above 130·C a thick red resin forms.
Reaction of LR and 184.
To LR (2.4 g. 5.9 mmol) was added toluene (22 ml) and 184 (3 ml. 2.6g. 37 mmol). This
mix1ure was stirred as it was heated until it started to reflux. Shortly after starting the heating
the LR dissolved to give a clear solution which then became cloudy again. The mixture was
heated under reflux for 30 minutes before being allowed to cool to room temperature. The
white solid was collected by filtration and washed with a little toluene, before being dried in
high vacuum to give 185 as a white solid (1.9 g. 5.6 mmol. 47 %). m.p. >190°C. (Found: C,
45.3; H, 5.2%; N, 17.5%. C13H'9N.oPS2 requires C, 45.6%; H, 5.6%; N, 16.4%). For a second
sample results were C 46.6%, H 5.7% and N 16.4%. IR 16275, 1571m, 15515, 1501m,
1442m, 1425m, 1205m, 1361m, 1304m, 1291m, 12585,1190m, 1181m, 11165, 1059m,
1022m, 9505, 8715, 8445, 828w, 802m, 72Ow, 6915, 638m, 627m, 588m, 541m, 529m, 496w,
478m, 439m, 413m, and 401 w (cm-'). op (ppm) 58.2. OH (ppm) 7.8 (2H, m), 6.8 (2H, m), 3.75 (3
191
H), and 3.1 (s). Oc (ppm) 162.0, 155.8, 132.7 [d J(PC)12 Hz], 130 [d 'J("P-13C)=154 Hz],
113.6 [d J(PC) 16 Hz], 55.7 and 37.8. MS(En mlz 342(M+), 272(M -Me2NCN), 202(M -
2Me2NCN), 171, 155, 139, 133, 123, 107,95,77,70,69,63, and 44. Molecular ion found at
342.0746 amu (12C'3'H'914N.'·03'p32S2 requires 342.07379 amu error of 2.4 ppm).
Reaction of 186 and LR
LR (0.970 g. 2.4 mmol) was treated with 186 (1.2 ml. 1.1 g. 9.9 mmol), the mixture was stirred
for 40 minutes before being heated in an oil bath (140°C for one minute) and then allowed to
cool to give a jelly-like mass. This was found to be insoluble in cold toluene, after
recrystallization from toluene a white solid (1.19g. 2.8 mmol. 59 %). By 'H NMR spectroscopy
this solid was found not to be pure. The solid was subject to a second recrystallization from
toluene to give 191 as a (0.73g. 1.7 mmol. 36 %). op, 58.1 ppm. OH (ppm) 7.9 [2H, dd (8.7 Hz
and 14 Hz)], 6.9 (2 H, m), 3.8 (s) and 3.6 (m) together the last two peaks (11.6H), 3.1 (1 H, m)
and 1.6 (15 H, m). 'H-'H COSY 01(ppm) [02(ppm)] 7.9 [6.9], 3.6 [1.6], 3.1[1.6].oc (ppm),
154.4(quat), 132.2 (d J(PC) 12 Hz), 113.2 (d J(PC) 15 Hz), 55.2,50 minor peak (CH2), 46.3
(CH2), 25.6 (CH2) and 24.6 (CH2).13C/'H Correlation 'H o(ppm) ['3C o(ppm)], 7.9 [132], 6.9
[113], 3.8 [55], 3.1 [50], 3.6 [46], 1.6 [26], 1.6 [25]. MS(EI) (m/q) 422 (M+ very weak), 316, 279,
254, 222, 196, 171. 139, 110, 84, 63, 42. Molecular ion found at 422.1368 amu,
12C'9'H2714N4'·031p32S2 requires 422.13638 amu (error of 0.9 ppm). CV irreversible oxidation,
measured by square wave voltammetry as 0.67 volt.
The mother liquors from the recrystallizations were combined and subject to flash column
chromatography to give after removal of solvent 190 as a colourless heavy oil (0.304g. 0.97
mmol. 20%) IR 3068w, 3005m, 2938s, 2852s, 2210m, 1965vs, 15965, 1570m, 1502s, 1462m,
1451m, 1442m, 1408m, 1375m, 1335w, 1307m, 1296s, 12595, 1205s, 11815, 11605, 11185,
1065s, 1026s, 990w, 953s, 904w, 853m, 8305, 804s, 735s, 712m, 6895, 640m, 620s, 527m,
500m, 467m, 443w, 425w, and 392w (cm-'). op 60.2 ppm. OH (ppm) 7.8 (2 H, m), 6.9 (2 H, m),
3.8 (3 H, 5), 3.2 (5 H, m), 1.6 (8 H, m). When the peak at 1.6 ppm is subject to irradiation the
peak at 3.2 changes to being a pair of doublets of doublets, 2J['H-'H]=12.7 Hz and 3J[31 p_
'H]=10.0 Hz for the proton resonance centred at 3.25 ppm while for the resonance centred at
3.11 ppm 3J[31 p_'H]=9.2 Hz. odppm) 163 (quat), 132 [d J(PC)13 Hz], 114 [d J(PC) 16 Hz], 56,
50 minor peak (CH2), 46 (CH2), 25.8 (CH2), 25.7 (CH2), 24 (CH2). MS (EI+) mlz 312, 279, 254,
238, 196, 171, 139, 110, 84, 59, 42 and 28. Molecular ion found at 312.0523 amu
(12C'3' H1714N2'·03' p32S2 requires 312.05199 amu, error of 1.1 ppm).
The reaction of FC2P2S4 and 184, where the concentration of 184 is maintained at a low level.
FC.P2S4 (9.6 g. 17.1 mmol) was suspended in toluene (100 ml) and heated up to reflux
temperature before 184 (6 ml. 5.2 g. 74.7 ml) dissolved in toluene (100 ml) was added
192
dropwise over 1 hour. This mixture was maintained at reflux temperature during the addition,
the FC2P2S, in the reaction mixture dissolved up to give a deep red solution as the 184 was
added. The mixture was allowed to cool before filtration. After removal of solvent the mixture
was subject to flash column chromatography (100 g Si02, elution with 500 ml 20% CH2CI2 in
petroleum ether, 1 L 30% CH2CI2, 500 ml 40% CH2CI2, 500 ml CH2CI2 and 1 L 10% EtOAc in
CH2CI2) to give 94 (4.08 g. 9.72 mmol. 28 %) and 95 (6.82 g. 19.5 mmol. 57 %) identical to
that from the above experiment. In addition another fraction was collected which on removal of
solvent gave a red oil that later solidified. lip (ppm) 81.0 (d, 42 Hz), 80.6 (d, 44 Hz), 52.6 m.
CV, reversible redox couple at 0.72 volt, with strong prepeaks on the leading edges. This red
solid was recrystalized from hot EtOAc (8 ml) to give 198 as an orange crystalline solid (81
mg. 132 I'mol. 1 %). By the slow cooling of a hot solution, in EtOAc, crystals were obtained.
m.p. 151-153°C.(Found: C, 43.3; H, 3.8; N, 4.2. C23H2.N2Fe2P2S30 requires C, 45.0; H, 3.9; N,
4.6 %). IR 3110w, 3092m, 3082m, 2933m, 2882w, 2844m, 2810w, 2079s, 2013vs, 1475w,
1453m, 1435w, 1410m, 1387w, 1366m, 1348w, 1311w, 1287m, 1188s, 1178s, 1106m,
1061w, 1053w, 1028s, 1000sh, 958s, 919vs, 896sh, 859w, 847w, 825s, 810sh, 736vs, 691s,
636w, 625m, 602w, 568s, 519sh, 500m, 489m, 465m, 425m, 382w, 366m, 341w, 329w, and
303w (cm-'). lip (ppm), 81.0 [d, 3 J(31 p _31 p )=44 Hz] and 52.1 [d, 3 J(31 p_31 p)=44 Hz]. IiH (ppm),
4.85 (m), 4.74 (m), 4.56 (m), 4.41 (s), 4.34 (m), 4.24 (s), Integration for the ferroceneyl area is
(18H). 2.80 (7 H, d, 13 Hz). lie (ppm) 73.3 (d J(PC) 22 Hz), 72.6 to 71.1 (m), 70.8, 70.5 (d
J(PC) 12 Hz), 70.5 and 37.7. MS(FAB) m/z 637 (M+Na)+, 614 (M+), 350, and 292. (Isotropic
distribution correct for C23H2.Fe2N2P2S30). MS(ES+) mlz 637 (M+Naf, 615 (MH)+, and 292.
MS(ES-) mlz 672,659,645 (M+OMef, 631 (M+OHr, 572, 381, and 335.
The mother liquor from the first recrystalization was examined by 31 p NMR spectroscopy, in
addition to isomer isolated above a second compound was present. The isomers were present
in a 2:1 ratio, the minor component being that isolated above. lip 81.0 (d, 41 Hz) and 53.2 (d,
41 Hz).
The reaction of FC2P2S, and 184 with water present.
FC2P2S. (4.06 g. 7.25 mmol) was suspended in THF (100 ml) and heated up to reflux
temperature before 184 (0.58 ml. 0.51 g. 7.29 mmol) and water (0.13 ml. 0.13 g. 7.22 mmol)
were added as a solution in THF (50 ml) over 22 minutes. After this addition a large amount of
orange solid remained in the reaction mixture, so a mixture of 184 (1.25 ml) and water (0.26
ml) were added. After a 5 minutes of heating under reflux, the mixture was allowed to cool to
room temperature before the THF was removed in vacuum. The residue was dissolved in
CH2CI2, Si02 was added, before the products were absorbed onto silica by removal of the
CH2CI2. The silica with the compounds adsorbed on it was added to the flash column.
Chromatography [silica (60 g) elution with 500 ml petroleum ether, 500 ml 20% CH 2CI2 in
193
petroleum ether, 500 ml 40% CH2CI2 in petroleum ether, 500 ml CH2CI2, 500 ml 20% EtOAc in
CH2CI2 and 40% EtOAc in CH2CI21 gave an orange fraction which on evaporation furnished 97
as an orange solid (330 mg. 0.42 mmol. 6 %). ("'P-{'H} and 'H NMR spectra identical to that
made elsewhere in this thesis).
The reaction of Fc,P,S. and 186, where the concentration of 186 is maintained at a low level.
Fe,P,S. (9.84 g. 17.6 mmol) was suspended in toluene (80 ml) and heated to reflux
temperature before 186 (8.1 ml. 7.7 g. 70 mmol) in toluene (80 ml) was added dropwise over 3
hours. This mixture was maintained at reflux temperature during the addition, Fe,P,S.
dissolving to give a deep red solution as the 186 was added. The mixture was allowed to cool
before filtration. After removal of solvent the mixture was subject to flash column
chromatography (1 ~Og SiO" 1 L 20 % CH2CI2 in petroleum ether, 1 L 30 % CH,CI, followed by
500 ml50 % CH2CI2) to give 189 (12.36 g. 35.15 mmol. 90 %).
The reaction of diferrocenyl dithiadiphopshetane disulfide with N-phenyl benzaldehyde imine.
Fe,P,S. (3.0 g. 5.36 mmol) and N-phenyl benzaldehyde imine (2 g. 11.0 mmol) were heated
at reflux in toluene (150 ml) for 16 hours. By TLC very little chemical change was occurred.
After about 8 hours of heating under reflux, xylenes (100 ml) were added to the mixture and
the mixture was heated under reflux (64 hours) before being allowed to cool. The mixture was
filtered through a pad of silica and this pad was washed with CH,CI2 (50 ml), From the
combined filtrates the solvents were removed in vacuum to give a red oil (8 g). This red oil on
standing showed some signs of crystallisation, the red oil was applied to a silica column (83 g)
and this column eluted (500 ml of 40% CH2CI, in petroleum ether followed by 500 ml of
CH2CI2), the red eluted liquid was combined and the solvent removed in vacuum to give a red
solid. This red solid was heated with ethyl acetate (160 ml) and the resulting mixture of red
liquid and orange solid was allowed to cool to room temperature. The inside of the flask was
scratched and the mixture was cooled in a freezer overnight. The orange solid was collected
by filtration and washed with ethyl acetate (10 ml) to give orange microcrystals (0.97 g. 1.57
mmol. 29 %) of 48. m.p. 180°C decomposes to a black solid not melting below 300°C. (Found:
C, 50.3; H, 3.7; N, 2.3%. C26H23NFe'P2S3 requires C, 50.4; H, 3.7; N, 2.2%). IR 3097m,
1736w, 1594m, 1497m, 1490m, 1407w. 1389w, 1363w, 1341w, 1304w, 1247s, 1191w, 1173s,
1106m, 1079w, 1034m, 1025s, 1001w, 944S, 909s, 880s, 867m, 845m, 825s, 751s, 736w,
690vs, 670m, 613w, 522s, 489s, 464s, and 412w (cm·'). op 64.2 ppm. OH (ppm), 7.2 (5H, m),
5.00 (1H, m), 4.87 (1H, m). 4.66 (m) and 4.57 (m) combined integration height of the last two
peaks is (3H), 4.28 (6H, s). Oc (ppm) 136.3 (quat), 129.2, 127.2, 126.4 (m), 78.6 (d, 118 Hz),
76.1 (m), 74.0 (m), 72.7 (m), 72.1 (m), and 70.6 (s). MS(FAB) rnIz 642, 619,505,498,481,
194
451,433,421,391,377,361,305,243,217,204,154,146, 136, and many peaks below 136.
Cyclic voltammetry; Redox couple is reversible and is at 0.77 volt.
The reaction of Fc,P,S. and N ,N' -dicyclohexylcarbodiimide) to form 199.
N,N'-Dicyclohexylcarbodiimide (0.72 g. 3.5 mmol) and Fc,P,S. (1.9 g. 3.4 mmol) were placed
in toluene (10 ml) and heated under reflux for 7 days. The toluene soluble compounds were
transferred to a flask and the solvent was removed to give a brown tar. This was subjected to
flash column chromatography (petroleum ether/ether 9:2 mix1ure) to give after removal of
solvent an orange solid (0.43 g). 0 31p-{'H} (ppm) minor peaks at 94 and 58.8, major peak at
60.9. On heating with ethyl acetate it was found that the orange solid that was insoluble in the
hot solvent, and on cooling no additional solid was precipitated after the addition of ethanol.
The orange solid was collected by filtration and dried (77 mg. 101 mmol. 3 %). This solid is
2,4-diferrocenyl-3-cyclohexyl 1,3,2,4-thiazadiphosphetane 2,4-disulfide (199). m.p.,
Decomposes above 220°C to a black solid, which does not melt below 280°C. (Found C,
49.1%; H, 4.5%; N, 2.2%. C,.H,.Fe,NP,S3 requires C, 49.9%; H, 4.6%; N, 2.2%). IR 3087m,
2929s, 2849s, 1448w, 1438w, 1407w, 1387w, 1364w, 1304w, 1266w, 1247w, 1191m, 1179m,
1171m, 1128m, 1106m, 1053w, 1033m, 1022m, 1001m, 936m, 914m, 873m, 864m, 844m,
821m, 746m, 701s, 679s, 617w, 535w, 519m, 492s, 456s, 409m, 349m, 325w (cm-'). op 61.0
ppm. OH (ppm), 4.96 (m), 4.88 (m), 4.61 (m), 4.55 (m) and 4.36 (s) the integration for the
ferrocenyl area (9.0H), 3.3 (br m), 1.55 (m) and 0.97 (m) the combined integration of the last
two peaks is (10.3H). On irradiation of the peak at 1.55 ppm the resonance at 3.3 ppm
changes to a broad 1:2:1 triplet like peak (lines observed at 3.35, 3.27, and 3.19 ppm). On
repeating this experiment at 233K (-40oC) this triplet appears to be sharper. Qc (ppm), 76.7 (d,
20 Hz), 73.7 (m), 72 (m), 70.4,57.8,33.1 (CH,), 32.2 (m, CH,), 25.7 (CH,), 25.3 (CH,), and
24.9 (CH,). MS(EI+) (m/z) 444, 248, 186, 121, 56. MS(FAB) (m/z) 625 (M+), 538, 346. CV,
reversible couple at 0.74 volt.
The reaction of Fc,P,S. with N-(2,4-dimethylphenyl) benzaldehyde imine to form 202.
Fc,P,S. (4.27 g. 7.63 mmol) and N-(2,4-dimethylphenyl) benzaldehyde imine (1.6 g) were
heated in toluene (70 ml) and xylenes (80 ml) for three days. After cooling the mixture was
filtered through a SiO, pad. This pad was washed with CH,CI, (4x50 ml) and these washings
were combined with the filtrate. The solvents were removed in vacuum to give a red oil (5.5 g).
Chromatography (64 g SiO,. elution with 500 ml of 20% CH,CI" 30% CH,CI" 40% CH,CI, in
petroleum ether followed by 500 ml CH,CI,) gave two orange fractions. On removal of solvent
the first fraction gave an orange solid which on ex1raction with hot ethyl acetate (ca 10 ml)
followed by cooling gave 2,4-diferrocenyl-3-(2,4-dimethylphenyl) thiazadiphosphetane 2,4-
disulfide (202) as an orange solid (548 mg. 0.847 mmol. 11 %). (Found: C, 52.2; H, 4.3; N, 2.2;
S, 15.0%. C,.H'7Fe,NP,S3 requires C, 52.0; H, 4.2; N, 2.2; S, 14.9%). IR 3096m, 3085m,
195
2958m, 2919m, 2857m, 1497m, 1451w, 1409m, 139Ow, 1377w, 1365w, 1349w, 1309w,
1257m, 1226m, 1193w, 1179s, 1129w, 1107w, 1058w, 1024s, 1005m, 952s, 914s, 888s,
864m, 825m, 811m, 801w, 734w, 714s, 687vs, 630m, 603w, 576w, 552m, 511sh, 503sh,
486m, 473sh, 486m, 473w, 460s, 451s, 408m, 365w and 355w (cm-'). op 66.9 ppm. oe (ppm)
139.4 (m, quat), 139.2 (m, quat), 132.4, 131.6 (m), 127.3, 74.2 (d, 13.6 Hz), 73.1 (d, 13.4 Hz),
72.4 (br d, 15.7 Hz), 71.0, 21.5, and 19.5. The aromatic area was re-examined with reduced
sweep width 139.44 (t, 3.6 Hz), 139.20 (t, 3.1 Hz), 132.43, 132.41, 131.63 (t, 4.0 Hz) and
127.32. OH (ppm): 6.79 (1 H), 6.64 (2 H), 5.04 (m, 2H), 4.64 (m, 2H), 4.59 (m, 2H), 4.48 (m, 2
H), 4.30 (s, 10 H), 2.10 (s, 3 H) and 1.93 (s, 3 H). MS(FAB) (m/z) 647 (M+), and 367. CV,
reversible redox couple observed at 0.78 volt, with prepeaks visible.
Reaction of LR and DCC.
LR (6.9g. 17 mmol) and N,N'-dicyclohexylcarbodimide (3.8 g. 18 mmol) were heated in
refluxing toluene (ca 60 ml) for 6 days. After filtration, the filtrate was diluted with 60-80
petroleum ether (55 ml). The addition of this petroleum ether caused very little precipitation of
solid. After the removal of all the solvent in vacuum, recrystallization from ethyl acetate (30 ml)
gave 2,4-bis(4-methoxyphenyl)-3-cyclohexyl 1,3,2,4-thiazadiphosphetane 2,4-disulfide (201)
as a white solid (2.28 g. 4.9 mmol. 29 %). (Found: C, 51.0; H, 5.0; N, 3.4. C2oH25N02P2S3
requires C, 51.2; H, 5.4; N, 3.0 %). IR 3067w, 3004m, 2932s, 2856s, 1591s, 1567m, 1497s,
1461sh, 1449s, 1410m, 1374w, 1349w, 1309m, 1293m, 1261s, 1180m, 1153w, 1101s,
1051w, 1023m, 1997w, 932s, 915m, 890w, 877s, 852m, 829s, 815m, 800m, 749m, 697s,
645w, 627m, 613s, 549s, 514w, 501s, 471w, 426s, 385m, 342w and 282w (cm-'). op, 60.2
ppm. oe (ppm), 163.5 (quat), 135.2 (m), 129.4 (quat), 127.7 (quat), 114.0 (m), 58.8, 55.5, 33.2
(CH2), 32.5 (m, CH2), and 25 (m, CH2). o'H (ppm) 8.4 (3H, dd, 3J[31 p_'H]=16 Hz, 3J['H-'H]=8.8
Hz), 7.0 (4H, dd, 4J[31 p_'H]=3.4 Hz, and 3J['H-'H]=8.8 Hz), 3.91 (6H, s), 3.4 (lH, s), 1.7 to 0.9
(12 H, m). MS(FAB) 492 (M+Na)+, 470 (M+H), 438 (M+H-S), 354, 277, 267, 234, 203, and
186 (m/z). M+H ion peak has isotropic distribution expected for C2oH26P202NS3'
After removal of the ethyl acetate from the mother liquor, the orange tar that remained was
distilled (3 mBar. 100-180·C air bath temperature), to give a colourless liquid (1.95 g. 14
mmol. 81 %). IR (thin film) 2937s, 2858m, 2186s, 2102vs, 2062s, 1450m, 1362m, 986w,
927m, 892w, 801w, and 641w (cm-'). OH 3.7 (lH, m) and 1.9 to 1.3 (11 H, m) oe (ppm) 55.3,
33.1 (CH2), 25.0 (CH2), and 23.2 (CH2). GCMS Single compound with a retention time of
10.776 minutes MS (El) (m/z) 141, 98, 83, 82, 67, 55, 41, and 39.
196
The reaction of FC2P2S, with tetraphenylphosphine imine
To a mixture of FC2P2S, (O.8 g. 1.43 mmol) and tetraphenylphosphine imine (1.0 g. 2.83 mmol)
was added dichloromethane (10 ml) and this mixture stirred at room temperature. FC2P2S,
was seen to rapidly react to give a red brown solution that was stirred overnight before being
filtered through a silica pad before removal of solvent. The red tar produced was dissolved in a
little hot ethyl acetate and allowed to cool. On cooling a solid crystallised out, this was
collected by filtration, after washing the crystals with ethyl acetate (O.25 g. 0.85 mmol. 30%) of
triphenylphosphine sulfide, as off-white crystals, was obtained. op 43.4 ppm.
Concentration of the mother liquor gave additional solid (0.46g. 1.58 mmol. 56 %). This solid
was stained orange by the mother liquor but on examination by 3' P NMR spectroscopy
revealed it to be identical to the first crop of crystals (op 43.4 ppm). The solvents were
removed from the mother liquor to yield a red tar (O.9 g) which solidified. This red tar was
found to be a complex mixture when examined by 31 p-{'H} NMR spectroscopy. op (ppm),
43.4,54.7,64.1,69.7,70.3 and 81.5. (Major peaks only).
The reaction of FC2P2S. with 2,6-dimethylaniline to form 203.
FC2P2S. (2.77 g. 4.94 mmol) and 2,6-dimethylaniline (5.25 ml. 5.2 g. 43 mmol) were mixed,
after stirring at room temperature (30 minutes) xylene (150 ml) was added and this mixture
heated under nitrogen (19 hours) before being allowed to cool. The mixture was filtered
through a Si02 pad which was then washed with CH2CI2 (2 portions of 50 ml). The filtrate was
evaporated down to give a blood red oil which was applied to a flash column (Si02 70 g)
elution with petroleum ether (300 ml) followed by 20% CH2CI2 in petroleum ether (500 ml) and
30% CH2Cl2 in petroleum ether (500 ml) gave fractions which by TLC contained an orange
product. These fractions were combined and the solvent removed in vacuum to give an
orange tar like solid. Recrystallization from ethyl acetate (90 ml) gave an orange solid (O.26 g).
To the mother liquor was added methanol (lOO ml) to give a second crop of orange
microcrystals. Both crops were combined and recrystalized from ethyl acetate to give 2,4-
diferrocenyl-3-{2,6-dimethylphenyl) 1,3,2,4-thiazadiphosphetane 2,4-disulfide (203) as an
orange solid (471 mg. 0.728 mmol. 15 %). (Found C, 51.3; H, 4.2; N, 1.8%. C2.H27NFe2P2S3
requires C, 51.9; H, 4.2; N, 2.2%). IR 1465m, 1409m, 1390w, 1381w, 1364w, 1311w, 1260w,
1197s, 1180s, 1170s, 1106m, 1056w, 1023s, 1003m, 946m, 907s, 883vs, 869w, 834w, 824s,
776m, 719s, 683vs, 63Ow, 582w, 558w, 532s, 491s, 457vs, 410m, and 342m (cm''). op (ppm),
63.9. OH (ppm), 6.97 (lH, m), 6.84 (2H, d, 7.5 Hz) , 5.14 (2H m), 4.74 (2H, m), 4.61 (4H, m)
4.38 (10H, s), 2.05 (6H, s). oe (ppm), 140.7 (m), 129.0 (t, 0.6 Hz), 128.3 (m), 77.0 (m), 73.3
(m), 70.8 (s), 21.1 (s). MS{FAB) (m/z) 647{M+), 582, 367, 302, 280, 248, 217. For M+ the
expected isotropic distribution was observed. CV, reversible redox couple at 0.78 volts.
197
Attempted synthesis of 205 by the reaction of FC2P2S, and N-Benzylidene 2,6-dimethylaniline.
Compound FC2P2S, (912 mg. 1.63 mmol) and N-Benzylidene 2,6-dimethylaniline (340 mg.
1.63 mmol) were heated in toluene (5 ml) at 130°C (sealed tube) for 20 hours. After cooling
chromatography (12 g Si02 elution with 100 ml petroleum ether, 100 ml CH2CI2 and 100 ml
15% EtOAc in CH2CI2) gave a trace of a red waYCj solid. This could not be purified by
recrystallization from EtOAc.
The reaction of heptamethyldisiliazane, tetrahydrofuran and Fc,P2S. to form 222.
Compound FC2P2S, (719 mg. 1.28 mmol) heptamethyldisiliazane (0.5 ml. 0.4 g. 2.29 mmol)
and THF (2 ml. 1.8 g. 25 mmol) were heated together in a sealed tube in an oil bath (50-70°C)
for 5 hours, to give a dark red solution. This after being allowed to stand for 10 hours before
the removal of all volatile material in vacuum.
Warning: Bis(trimethylsilyl) sulfide has an extremely strong unpleasant smell like that of
butane thiol. When evaporating any reaction mixture which might contain bis(trimethylsilyl)
sulfide do so using a high vacuum line fitted with a trap cooled by liquid nitrogen. After the
evaporation, while the trap contents are still frozen add sodium hypochlorite solution and
allow to stand.
This tar was found to be soluble in petroleum ether, chloroform, and ethyl acetate. After being
dissolved in petroleum ether it was filtered through AI,03' the AI20 3 pad was washed with
petroleum ether until the filtrate was no longer orange in colour (circa 50 ml petroleum ether
used). Evaporation of the petroleum ether gave P-(trimethylsilyl-methylamino) 5-(4-
trimethylsiloxybutyl) P-ferrocenyl dithiophosphonate (222) as an syrup like orange oil (803 mg.
1.52 mmol. 66 %) which, on standing, solidified. Mp 44-46°C. IR 3100m, 29535, 29075, 28645,
2817m, 1452m, 1436m, 1412m, 1387m, 1368w, 1299w, 1261sh, 12505, 1196sh, 11805,
11705, 11005, 10635, 10275, 1003m, 964m, 9035, 8825, 8435, 7595, 7365, 7015, 691sh,
645m, 6285 (cm-'). 5'H (ppm): 4.62 (m), 4.47 (m), 4.37 (m), 4.34 (m), 4.28 (5). Total
integration for area 4.7 to 4.2 ppm is 9 H, 3.59 (2 H, t, 6.1 Hz), 2.9 (2 H, m), 2.4 (3 H, d 3 J[3'p_
'H)=16 Hz), 1.7 (4 H, m), 0.28 (9 H, 5), 0.09 (8 H, 5).
198
Chemical shift of
irradiated peak
8(ppm)
1.71
2.89
3.61
Table 6.12 'H-'H double irradiation experiments.
Chemical shift of peak Change
where change occurs.
o(ppm)
3.60
2.89
1.7
1.7
triplet changes to a singlet.
complex multiplet changes to a poorly
poorly resolved pair of doublets of doublets.
The downfield half of the peak becomes
slightly more simple.
The upfield half of the peak becomes
slightly more simple.
o31p-{'H} (ppm): 82.7 ppm. o13C-{'H} (ppm): 58.9 (CH2), 30.1 , 28.6 (CH2), 26.5 (CH2), 23.4
(CH2), 0.0, -3.8. 13C/'H Correlation ('3C 10-70 ppm, 'H 1.0-5.0ppm). 03C (ppm) o'H (ppm)
58.9 (3.6),30.1 (2.4),28.6 (1.7), 26.5 (2.9), and 23.4 (1.7). MS(FAB) (m/z) 527(M+), expected
isotropic distribution observed for molecular ion. Cyclic voltammetry, reversible redox couple
at 0.66 Volt.
Reaction of Fc,P,S. with carboanailide (117) (N,N'-diphenyl urea) to form 48.
Fc,P,S. (2.8 g. 4.9 mmol) and 117 (2.0 g. 9.4 mmol) were heated under reflux in xylene (100
ml) (17 hours) before being allowed to cool, filtration through silica, followed by washing the
silica pad with CH2CI2 gave on evaporation a brown tar (3.6 g). Flash column chromatography
on silica (38 g elution with petroleum ether/CH2Cl2). gave an orange material (225 mg. 316
flmol. 3 %) (48). m.p. circa 180·C d. IR 3098m, 1594m, 1497m, 1491m, 1247s, 1180s, 1173s,
1106m, 1034m, 1025s, 943s, 909s, 881s, 867w, 845w, 825m, 751m, 736w, 690 vs, 670m,
618w, 522m, 489s, 405s, 412w, 359w, and 336w (cm"'). op (ppm), 64.3 ppm. OH (ppm) 7.19
(m) and 7.16 (4 H, m), 4.93 (lH, m), 4.80 (lH, m), 4.58 (lH, m) 4.50 (lH, m), 4.21 (5 H, s).
Cyclic voltammetry; RedOX couple is reversible and is at 0.77 volt. This solid is slightly impure
2,4-diferrocenyl-3-phenyl 1,3,2,4-thiazadiphosphetane 2,4-disulfide. Almost all the solid was
dissolved in ethyl acetate and the resulting solution was allowed to cool to give red crystals.
Further elution with CH2CI,Ipetroleum ether mixtures gave more orange fractions, evaporation
gave an orange solid (674 mg) (49). This solid was recrystallized from ethyl acetate to give
after drying two crops of an orange yellow solid (222 mg) and (123 mg). IR 3367m, 3289m,
199
32475, 3042m, 17225, 1654w, 15995, 14985, 14005, 1321w, 12815, 1240m, 12265, 1175m,
1108w, 1077w, 10295, 999m, 9435, 9105, 894m, 856w, 840W, 826m, 799m, 772w, 7565,
746s, 694s, 676s, 637w, 617w (cm-'). OH (ppm) 7.2 (m), 7.0 (t), 5.2 (d), 4.65 (m), 4.42 (m),
4.34 (s), 4.13 (q), 2.05 (s) and 1.26 (t).
This solid contained ethyl acetate, to remove this, the solid was recrystallized from toluene to
give an orange yellow solid (230 mg. 532 flmol. 6 %). (Found C, 60.4; H, 4.6; N, 6.3;
C22H21N2Fe2PS requires C, 56.9; H, 4.6; N, 6.0%). IR (KBr) 3382s, 3243s br, 3087w, 3042w,
3019w, 1599s, 1496s, 1474sm 1401m, 1383s, 1324w, 1301sh, 12835, 1225m, 1192w,
1179sh, 1172m, 1106w, 1078w, 1031m, 1000w, 948s, 915s, 892m, 829m, 791w, 753s, 694s,
674s, 637w, 616w, 599m, 578w, 564w, 524w, 501w, 488m, 474s, 437sh, 417m, 390w and
356w (cm-'). IR (CH2CI2) 3388m, 1605s, 1503m, 1387m, 1271m (cm-'). op 54.5 ppm. OH (ppm)
.7.2 (8 H, m), 7.0 (2 H, t), 5.2 (2 H, d 12 Hz), 4.65 (2 H, m), 4.42 (2 H, m), 4.34 (3 H, s). oe (ppm) 139.6 (quat), 129.2, 122.6,119.5 (d, 6 Hz), 72.3 (d, 14 Hz), 71.4 (d, 12 Hz), and 70.2.
CV; Almost reversible redox couple showing signs of slow electron transfer. With a scan rate
of 100 mV s-' the redox couple is 0.63 volt. MS(EI) mlz 432 (M+), 340 (M-PhNH2)+, 274, 248,
217,186,155,122, and 93. Molecular ion at 432.0512 amu, [,2C22'H2114N232S3'pS6Fe requires
432.05120 (within 0.1 ppm)].
The reaction of FC2P2S, with N,N'-dimethyl-N,N'-diphenyl urea to form 96.
N,N'-dimethyl-N,N'-diphenyl urea (2.6 g. 11 mmol) was dissolved in xylenes (150 ml), to this
was added FC2P2S. (3 g. 5.4 mmol). This mixture was heated under reflux for 17 hours. After
being allowed to cool the xylene was removed in vacuum to give a red tar that wa5 subjected
to flash column chromatography on silica (50g. 500 ml 20% CHCI3 in petroleum ether (60-80),
500 ml of 50% CHCI3 in petroleum ether followed by CHCI3). An orange fraction was collected,
which after removal of the solvent gave a red oil. This red oil became a solid that was then
recrystallized from ethyl acetate to give 96 as an orange powder (257 mg. 324 flMol. 9%). Mp
233-235°C melts with decomposition. (Found ;C, 45.3; H, 3.6; N 0.0; S, 11.8%.
C30H27Fe3P303S3 requires ;C, 45.5; H, 3.4; N, 0.0; S, 12.1%). IR 3095m, 1412m, 1391w,
1370w, 1351w, 1316w, 1191s, 1107m, 1057w, 1029m, 1000w, 942vs, 894s, 865w, 841sh,
822m, 798m, 758s, 680m, 666m, 488m, 471s, 428m, 403w, 341w (cm-'). op (ppm), 76.59 (dd,
2J[3'p_3'PJ=54 Hz and 2J[31 p_3'PJ=46 Hz), 74.47 (d, J2[3'p_31 PJ=53 Hz, and 74.48 (d, J2[3'p_
31PJ=47 Hz). OH (ppm), 4.96 (2H, m), 4.85 (2H, m), 4.60 (2H, m), 4.54 (2H, m). 4.47 (2H, m),
4.40 (2H, m), 4.35 (5 H, s), and 4.25 (10 H, s). oe (ppm), 74.0 to 72.9 (m), 72.2 (m), 71.1 (s).
MS(FAB) mlz 792(M+), and 727 (M-CsHs)+ Expected isotropic distribution was observed for
M+. CV; Reversible but broad redox couple observed at 0.81 volt.
200
The synthesis ofN-methyl N,N'-diphenyl urea.
Phenyl isocyanate (46 ml. 50 g. 420 mmol) was added cautiously, over 30 minutes, to N
methyl aniline (50 ml. 49.5 g. 462 mmol) dissolved in CH2CI2 (50 ml). An exothermic reaction
occurred and the phenyl isocyanate added at such a rate to maintain a gentle reflux. After
stirring for 30 minutes, the CH2CI2 was removed in vacuum to give an off white solid. This was
recrystallized from hot ethanol (10 ml) before being stirred with hot petroleum ether (60-80°C
fraction) (500 ml), after cooling the white solid was filtered off and dried in vacuum to give N
methyl N,N'-diphenyl urea (82.5 g. 365 mmol. 94%). o'H (ppm) 7.47 (t, 7.4 Hz), 7.3 (m)
combined integration for the multiplets and the triplet (9H), 6.99 (1H, t, 5.8 Hz), 6.3 (1H, br),
3.32 (3H, s). o'3C-{'H} (ppm) 154.4 (quat), 143.0 (quat), 139.0 (quat), 130.3, 128.8, 127.8,
127.4,122.8,119.3, and 37.3.
Warning: Phenyl isocyanate is toxic and a ~ irritant. Avoid all contact, and take care to
decontaminate glassware before cleaning. Small traces of Ph NCO can be destroyed using
ethanol.
The reaction of FC2P2S. with N-methyl-N,N'-diphenyl urea.
N-methyl-N,N'-diphenyl urea (4 g. 17.7 mmol) and Fc,P2S. (5.24 g. 9.4 mmol) in xylenes (150
ml) was heated under reflux (17 hrs). After cooling, chromatography on SiO, (97 g. elution with
300 ml petroleum ether, 1 I 40% CH,CI, in petroleum ether, 500 ml CH,CI" and 500 ml 20%
EtOAc in CH2CI,), followed by recrystallization from ethyl acetate (50 ml) gave 96 as an
orange powder (1.38 g. 1.74 mmol. 29 %). 3'P-{'H} and 'H NMR spectra identical with that
made from N,N'-dimethyl-N,N'-diphenyl urea.
201
Chapter 7
Electrochemical Characterization by Cyclic Voltammetry.
The electronic effects of the phosphorus portion of the molecule on the ferrocene were of
interest. From the literature data for ferrocenes with chalcogen or phosphorus atoms bonded
to the ferrocene, 45, 194 it appears that these atoms have an electron withdrawing effect on the
ferrocene (Scheme 7.1).
S S S
~s ~s 0/\ ~s S\ $~ $\ Fe / Se Fe / Se Fe S Fe / s
0-1 0-1 rb;-I rtf-I 0.90V 0.93 V 0.72 V 0.95 V
o/S\
K50 Fe Se
O-i 0.64 V 0.23V 0.39V
Scheme 7.1 Ferrocenes with and without sulfur and selenium containing groups attached.
The results which were obtained with our compounds are similar, all our compounds are more
difficult to oxidize than ferrocene suggesting that the phopshorus portion of the molecule is
electron-withdrawing.
For most of those compounds examined in this work by CV (Figure 7.1 and Table 7.1) , a
single reversible or quasi-reversible redox change is observed. Those compounds for which
several sequential oxidations occur have already been disscussed in Chapter 6. In some
cyclic voltammograms a shoulder is seen as a prepeak on the reducing wave, this suggests
202
that slight absorption on the surface of the electrode may have occured. Despite the fact that
sulfur has a high affinity for platinum (and other group 10 metals), strong absorption of the
compounds to the electrode was not seen, which suggests that the compounds do not have a
great affinity for platinum. In Table 7.1 the compounds are grouped according to the nature of
the atoms bonded to the phosphorus.
s 11 p-y
Fc"-"- \ X
Figure 7.1 General structure of the P-ferrocenyl compounds.
The replacement of the endocyclic sulfurs in Fc2P2S, with other atoms (or groups) made the
redox couple increase. This is likely to be due to the greater electronegativities of the new
atoms. By changing groups remote from the ferrocenyl group (3 bonds away) very little
change occurs to the redox couples. A weak relationship between redox potential and the
electronegativities ,03 of the atoms directly bonded (Ignoring the ferrocene group and the
double bonded sulfur) to the phosphorus has been found (Figure 7.2). The point at 5.5 on the
electronegativity scale appears to be a rogue point.
0.85
0.8 W c; 0.75 • ~ • .,
0.7 ;:: c ., •• - 0.65 0 Co • " 0 0.6 .., ., c:
0.55
0.5
4 4.5 5 5.5 6 6.5 7
Electronegativity
0
Figure 7.2 A graph of redox potential against electronegativity of the attached atoms.
203
Table 7.1 Electrochemical data for P-ferrocenyl compounds.
X y Compound El/2 (volts) Formula
S S 12 0.63(0.52)c FC'2P2S•
S S 42 0.54b FCP(S)S2Pt(PEtah
S S 152 0.71" FcP(S)-S-CHPh-CHPh-S-
S S 45 0.76" FcP(S)-S-CHPh-S-CHPh-S-
(0.66 Mean)
C S 43 0.70 FcP(S)SC7H.
C S 176 0.67 FcP(S)SC7HlO
C S 44 0.65" FcP(S)SC.Me.
C S 96 0.66 FcP(S)-CH,-CMe=CMe-CH2-S-
C S 179 0.66b FcP(S)(C.Hg)SBn
C S 181 0.69 FcP(S)(C.Hg)S-2,4-dinitrophenyl
(0.67 Mean)
N S 207 0.66 FcP(S)(NMeTMS)S(CH2).OTMS
N S 48 0.77 FC,P2S3NPh
N S 201 0.74 FC,P2S3NCy
N S 204 0.78 Fc2P2S3N-2,4-dimethylphenyl
N S 205 0.78 Fc2P2S3N-2,6-dimethylphenyl
N S 185 0.80 FC,P2S3NBn
(0.76 Mean)
N N 49 0.63" FcP(S)(NHPhh
N N 95 0.74 FcP(S)(NMe2)(NCS)
N N 188 0.72 FcP(S)(Pip)(NCS)
N N 94 0.56b FcP(S)-N=C(NMe,)-S-C(NMe2)=N-
N N 190 0.53/0.87" FcP(S)-N=CPip-S-CPip=N-
(0.64 Mean)
N 0 200 0.72 FcP(S)(NMe2)OP(S)(NCS)Fc
0 0 97 0.81 FC,Pa0 3S3
0 0 151 0.80 F cP(S)O,C.H2( lerf-C.Hg),
(0.81 Mean)
" Redox couple is quasi-reverseable showing slow electron transfer." A small shoulder was
seen as a prepeak on the reducing wave.c Redox couple was altered to take account of the
two methyl groups on the ferrocenyl groups. The original redox couple is in bracketsd A
second redox couple is seen, which is not reversable.
204
A graph of redox potential plotted against the 31 p NMR chemical shift (op) shows no clear
correlation (Figure 7.3). Likewise no clear relationship exists between either P=S distance
(Figure 7.4) or v(P=S) and redox potential (Figure 7.5).
D.'
D.'
0.7 ., ~ 06
~ 0.5 1: .. '004 Co X .g 0.3 .. It:
0.2
0.1
0 0
•
20 40
• •
• • •• • ~ . .
• •
• •
60
• ••
'"
• •
Phosphorus NMR chemical shift (ppm)
•
100
Figure 7.3 Graph of redox potential aganist the 31p chemical shift (op).
Redox potential vs P=S bond length.
1.95 .<: • - 1.94 • • ..,- •• c .., • • .. c 1.93 • • - co .... ~ 1.92 cUi • ; • co .., ... c 1.91 VlS. 1.9 •
11 c.. 1.89 0.5 0.55 0.6 0.65 0.7 0.75
Potential of redox couple (Volts)
•
0.8
Figure 7.4 Graph of phosphorus sulfur double bond length aganist redox potential.
120
205
0.8
• 0.75 •
=- • co • ~ 0.7 •
"(ij ;> c • .. 0.65 • -co • Co
" 0.6 -co ..., .. c:: • 0.55 •
0.5 630 640 650 660 670 680 690 700 710
Frequency (wavenumber cm-1)
Figure 7.5 Graph of P=S stretching frequency against redox potential.
206
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213
Crystallographic data
Compound Fc,P,S. (MFDW1) 148 (MFDW5) 31 (MFDW2) Formula C20H,.Fe,P,S. C,.H13FePO,S C"H3.FeP3PtS3
Colour,Habit orange, needle orange, plate yellow, hexagon Crystal size (mm) 0.08xO.08xO.33 0.11 xO.05xO.05 0.32xO.35xO.12 Crystal system monoclinic monoclinic monoclinic Space group P21/n P2 l1n P2 1/n
Unit cell dimensions (A) a 6.431 (4) 13.816(2) 15.515(5) b 12.616(3) 7.402(4) 10.817(10) c 13.461(3) 16.215(2) 17.167(13) p(") 93.62(3) 113.05(1) 98.90(5) Volume(A'j 1090 1526 2846 Z 2· 4 4 Formula weight 560.2 356.2 743.6 p(calc) Mgm"" 1.71 1.55 1.74 Absorption CoefficienUmm-1 15.7 10.2 17.0 F(OOO) 568 728 1472 Ind.Refl. (R~,%) 1719(9.1) 2483(8.2) 4479(7.8) Observed Refl. (1)3.0,,(1)) 959 1345 2815 No of Parameters Refined 128 191 272 Data/Parameter ratio 7.5 7.0 10.3 MinlMax transm. 0.65/1.0 0.8211.0 0.60/1.0 Weighing Scheme p= 0.009 0.001 0.001 Final R,Rw 4.0,4.4 3.8,2.4 4.5,3.9 Largest 1>/" 0.00 0.07 0.81 Largest Difference 0.33/-0.30 0.25/-0.24 0.96/-2.59b
Peak/Hole (eA"")
• The molecule is disposed about a crystallographic centre of symmetry b The largest difference peak is located close to the platinium atom. Unless otherwise stated all measurements were made using Cu-Ka radation.
Compound 152 (MFDW18) 45 (MFDW20) LR* (M FDW21 ) Formula C"H21 PS3Fe C,.H21 PS.Fe C"H30D,P,S. Colour,Habit yellow, plate yellow, cube clear, needle Crystal size (mm) 0.06xO.l0xO.20 0.18xO.18xO.18 0.1 OxO.l OxO.28 Crystal system triclinic triclinic triclinic Space group pi (#2) pi (#2) pi (#2) Unit cell dimensions (A) a 12.232(1) 11.219(2) 9.597(2) b 14.473(2) 11.614(1) 12.089(2) c 6.750(1) 10.977(2) 5.986(2) a(") 99.56(1) 107.34(1) 102.00(2) P 92.68(1) 118.54(2) 99.92(2) Y 68.671 (7) 89.35(1 ) 95.61 (2) Volume(A3
) 1097.5(3) 1184.6(4) 662.7(2) Z 2 2 1 Formula weight 492.43 524.49 516.67 p(calc) Mgm·3 1.490 1.470 1.295 Absorption CoefficienUmm-1 8.922 9.10 4.563 F(OOO) 508.00 540.00 272.00 Ind.Refl. (R",%) 3262(0.240) 3522(0.070) 1979(0.064) Observed Refl. (1)3.0,,(1)) 2482 2423 1538 No of Parameters Refined 263 272 137 Data/Parameter ratio 9.44 8.91 11.23 MinlMax transm. 0.57/1.00 0.71/1.00 0.7211.00 Weighing Scheme p= 0.0030 0.0030 0.0050 Final R,Rw 0.035,0.034 0.040,0.038 0.056,0.057 Largest 1>/" 0.03 0.03 Largest Difference PeakIHole (eA",) 0.29/0.29 0.034/0.34 0.53/-0.42
214
Compound 199 (MFDWll) 48 (MFDWI5) Formula C26H,.NP2S3Fe2 C26H23NP2S3Fe2 Colour,Habit orange, block orange, prism Crystal size (mm) 0.10xO.23xO.28 0.08xO.I2x0.21 Crystal system orthorhombic orthorhombic Space group Pbcn (#60) Pbcn (#60) Unit cell dimensions (A) a 17.260(5) 16.723(2) b 15.020(3) 14.861(2) c 10.333(4) 10.216(3) Volume(A") 2678(1) 2538(1) Z 4 4 Formula weight 625.34 619.30 p(calc) Mgm-3 1.550 1.620 Absorption Coefficientlmm-1 12.13 12.794 F(OOO) 1288.00 1264.00 Reflec!ions 2304 2186 Observed Refl. (1)2.0,,(1)) 840 948 No of Parameters Refined 170 152 Data/Parameter ratio 4.94 6.24 Min/Max transm. 0.89/1.00 0.63/1.00 Weighing Scheme p= 0.0070 0.0000 Final R,Rw 0.041,0.038 0.048,0.035 Largest 6/" 0.26 1.08 Largest Difference Peak/Hole (eA-3)
0.24/-0.27 0.36/-0.39
Compound 48 (MFDWI4) 94 (MFDW6) Formula C22H2,N2PSFe C,.H2, FeN4PS2 Colour,Habit yellow, block yellow, plate Crystal size (mm) 0.20xO.20xO.25 0.20xO.20xO.l0 Crystal system monoclinic monoclinic Space group P2,/n (#14) P2,/n (#14) Unit cell dimensions (A) a 9.568(2) 13.084(4) b 12.6641(9) 7.897(6) c 16.383(2) 18.364(5) p(') 92.24 97.31(2) Volume(A') 1983.6(4) 1882(1) Z 4 4 Formula weight 432.30 420.31 p(calc) Mgm-3 1.447 1.483 Absorption CoefficienUmm-1 7.903 9.344 F(OOO) 896.00 872.00 28 max (') 120.1 120.1 Ind.Reft. (R",%) 3143(0.070) 3038(0.062) Observed Reft. (1)2.0,,(1)) 1832 1820 No of Parameters Refined 245 218 Reflec!ionlParameter ratio 7.48 8.35 MinlMax transm. 0.6411.00 0.7311.00 Weighing Scheme p= 0.0030 0.0050 Final R,Rw 0.041,0.035 0.040,0.038 Largest 6/" 0.01 0.01 Largest Difference 0.26/-0.22 0.32/-0.45 Peak/Hole (eA",,)
215
Compound 43 (MFDW7) 44 (MFDW12) 95 (MFDW10) Formula C"H"FePS2 C22H2,PS2Fe C'3H15N2PS2Fe Colour,Habit yellow, plate yellow, plate yellow plate Crystal size (mm) 0.10xO.21xO.30 0.08xO.12x0.21 0.16xO.20xO.06 Crystal system monoclinic monoclinic monoclinic Space group P2,/c (#14) P2,/c (#14) P2,1c (#14) Unit cell dimensions (A) a 11.688(2) 10.616(2) 7.6883(9) b 9.508(2) 9.604(1) 20.6140(9) c 14.706(2) 21.033(2) 9.8804(9) ~(') 104.11(1) 101.264(10) 90.700(9) Volume(A"l 1584.9(4) 2103.1(4) 1565.8(2) z 4 4 4 Formula weight 372.26 442.40 350.22 p( calc) Mgm.:! 1.560 1.397 1.486 Absorption CoefficienUmm-1 10.98 8.334 11.073 F(OOO) 768.00 928.00 720 Ind.Refl. (Rin1%) 2559(0.267) 3339(0.148) 2415(0.059) Observed Refl. 1996 (1)3.0,,(1)) 2473 (1)2.00,,(1)) 1359 (1)2.00,,(1)) No of Parameters Refined 191 236 173 RefleclionlParameter ratio 10.45 10.48 7.86 MinlMax transm. 0.51/1.00 0.75/1.00 0.81/1.00 Weighing Scheme p= 0.0010 0.0020 0.0120 Final R,R,. 0.049,0.0446 0.038,0.031 0.037,0.037 Largest I!./" Largest Difference 0.57/-0.59 0.24/-0.22 0.29/-0.18 Peak/Hole (eA.:!)
Compound 41 185 (MFDW23) Formula C,.H'9PS2Fe C2,H25NP2S3Fe2 Colour,Habit yellow, prism orange, prism Crystal size (mm) 0.10xO.l0xO.18 0.1 OxO.l OxO.30 Crystal system monoclinic monoclinic Space group P2,/c (#14) P2,/c (#14) Unit cell dimensions (A) a 6.875(3) 7.347(2) b 12.459(4) 14.262(3) c 19.496(6) 25.660(2) ~(') 96.91 95.75(1) Volume(N) 1658.0(10) 2675.3(8) Z 4 4 Formula weight 362.27 633.32 p(calc) Mgm·3 1.451 1.572 Absorption CoefficienUmm-1 10.473 12.154 F(OOO) 752.00 1296.00 29 max (') 120.3 120.2 Ind.Refl. (R;",%) 2708(0.287) 4194(0.348) Observed Refl. 1665(1)3.00,,(1)) 2100(1)3.00,,(1)) No of Parameters Refined 182 317 Reflection/Parameter ratio 9.15 6.62 Min/Max transm. 0.43/1.00 0.25/1.00 Weighing Scheme p= 0.0070 0.0060 Final R,Rw 0.070,0.071 0.060,0.058 Largest I!./" 0.45 0.03 Largest Difference PeakIHole (eA "l
0.59/-0.43 0.56/-0.77
216
Compound 42 (MFDW8) 198 (MFDW19) 46 (MFDW22) Formula C'3H'5PS,Fe C"H,.N,P,S3Fe,O C,oH"FePS. Colour,Habit yellow, prism yellow, block Crystal size (mm) 0.10xO.10xO.23 0.21xO.21xO.23 0.15xO.13xO.13 Crystal system triclinic triclinic monoclinic Space group pI (#2) pT (#2) P2,1c Unit cell dimensions (A) a 10.7076(9) 11.776(3) 12.0594(9) b 11.361(1) 12.172(2) 18.3884(13) c 9.533(1) 9.949(1) 11.6422(8) a(") 105.700(8) 106.28(1) 90
P 94.633(8) 108.82(1) 114.6020(10)
Y 76.127(7) 80.96(2) 90 Volume(A') 1083.6(2) 1292.2 2347.3(3) Z 4 4 4 Formula weight 452.39 614.28 484.49 p(calc) Mgm·3 1.386 1.579 1.371 Absorption CoefficienVmm-1 8.122 12.60 1.069 F(OOO) 472.00 628.00 1016 29 max (") 120.2 120.1 Ind.Refl. (R;ot%) 3232(0;046) 3847(0.089) 3151(0.0165) Observed Refl. 1913 (1)2.00,,(1)) 2599 (1)3.00.,(1)) 3151 No of Parameters Refined 245 299 236 Reflection/Parameter ratio 7.81 8.69 13.35 Min/Max transm. 0.51/1.00 0.79/1.00 No absorption
correction made Weighing Scheme p= 0.0050 0.0000 Final R,Rw 0.046,0.41 0.042,0.039 0.0432,0.1092 Largest t;/" 0.16 0.22 Largest Difference 0.34/-0.40 0.32/-0.42 0.390/-0.373 Peak/Hole (eA,,)
Mo radation used
217
