3 Halogenophosphines and Related Compounds

BY J. A. MILLER

1 Halogenophosphines

The number of papers in the field of halogenophosphines has risen dramatically this year, and this has necessitated the omission of a significant number of papers from this survey. In general these have reported isolated reactions of a routine nature. There has been almost no new preparative work described this year, and the section has accord- ingly been divided into sub-sections on physical aspects and on chemical reactions.

Physical Aspects.-Interest continues in the question of the participation of d-orbitals in the bonding in phosphorus trihalides and their oxides. A number of ab initio calculations have been applied to phosphorus trihalide~,l-~ and there is general agreement that the inclusion of d-orbitals in the basis set gives a better bonding picture in the fluoride 1, 3, * and although in the higher halides the d-orbital contribution to the phosphorus-halogen bonds is very small. The oxyhalides have considerable d-orbital participation in the phosphoryl b0nd.l~ 2t Recent comment by CouIson,6 that the inclusion of d-orbitals in the basis set for MO studies need not necessarily be of chemical significance, even when improved wave-functions result, has been extended by Ratner and Sabin,6 who suggest that symmetry considerations of the state in question could be used to give some indication of the desirability of including d-orbitals. Photoelectron spectroscopy has been used to measure the binding energy of phosphorus trifluoride and trichloride,* and their oxides,7, * and the results are in good agreement with ab initio calculations.

E.s.r. studies of phosphorus trichloride and pentachloride, and n.q.r. studies lo of 35CI nuclei in phosphorus trichloride and a series of substituted

A. Serafini, J.-F. Labarre, A. Veillard, and G. Vinot, Chem. Comm., 1971, 996. I. H. Hillier and V. R. Saunders, J . C. S. Dalton, 1972, 21. M. F. Guest, I. H. Hillier, and V. R. Saunders, J . C. S. Faruduy 11, 1972, 68, 114. M. F. Guest, I. H. Hillier, and V. R. Saunders, J. C. S. Faraduy 11, 1972, 68, 867. C. A. Coulson, Nature, 1969, 221, 1106.

e- M. A. Ratner and J. R. Sabin, J. Arner. Chem. SOC., 1971, 93, 3542. P. J. Bassett and D. R. Lloyd, J. C. S. Dalton, 1972, 248. M. Barber, J. A. Connor, M. F. Guest, I. H. Hillier, andV. R. Saunders, Chem. Comm., 1971, 943. A. Begum and M. C. R. Symons, J. Chem. SOC. (A), 1971,2065.

lo J. K. B. Bishop, W. R. Cullen, and M. L. C. Gerry, Cunud. J. Chem., 1971, 49, 3913.

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52 Organophosphorus Chemistry

derivatives, have been published. Infrared and Raman spectra of various derivatives of phosphorus trichloride l1, l2 and oxychloride l3 have also appeared. A rationalization, based on Ramsay's equation, has appeared for the 'anomalous' order of 31P n.m.r. shifts of the phosphorus trihalides.la The halogenophosphine (1) has been observed to show separate N-methyl and O-methyl absorptions in (31P-decoupled) lH n.m.r. spectra run at

( MeONMe),PCI H,N P F,

( 1 ) (2)

low temperatures,16 and this has been interpreted as resulting from restricted rotation about the phosphorus-nitrogen bond. Aminodifluoro- phosphine (2) has a very short phosphorus-nitrogen bond, and the nitrogen is planar.16 At low temperatures the hydrogens are equivalent, possibly owing to rotation about the phosphorus-nitrogen bond.ls

Reactions.--NucZeophiZic Attack by Phosphorus. Alkyldichlorophosphines (3) undergo a mild Arbusov reaction with acid chlorides to give

0 II

I (3) 0 ~ 3

(4)

R1PCOR2 i, A

R'PCI, + R2COCl i i , R30,-i t

R' Me or Et

adducts which yield phosphinates (4) on treatment with alcoholic a1kali.l' Details have appeared of the reaction of chlorodiphenylphosphine ( 5 ) with a number of alkyl benzoates (6).18 The enhanced rate of (6; R = CN) over (6; R = H) was used as evidence for the nucleophilic role of the phosphine (5 ) in reactions which lead to two sets of products, as illustrated in Scheme 1 . Attack at the carbonyl group is not observed with the ester (6; R = OMe), and an unusual cleavage of the methoxy- group occurs. Chlorine and bromine both form phosphorane adducts with the difluorophosphines (7), and 19F and lH n.m.r. data of the phos- phoranes have been discussed (see Section 2, p. 63).

l1 N. Fritzowsky, A. Lentz, and J. Goubeau, 2. anorg. Chem., 1971, 386,67. l2 N. Fritzowsky, A. Lentz, and J. Goubeau, 2. anorg. Chem., 1971, 386,203. rA D. Kottgen, H. Stoll, A. Lentz, R. Pantzer, and J. Goubeau, Z . anorg. Chem., 1971,

385, 56. l4 L. Phillips and V. Wray, J. C. S. Perkin II. 1972, 214. l5 A. Hung, and J. W. Gilje, J. C . S. Chem. Comm., 1972, 662. l6 A. H. Brittain, J. E. Smith, P. L. Lee, K. Cohn, and R. H. Schwendemann, J . Arner.

Chem. SOC., 1971,93, 6772. l7 S. Kh. Nurtdinov, N. M. Ismagilova, T. V. Zykova, R. A. Salakhutdinov, V. S.

Tsivunin, and G. Kh. Kamai, Zhur. obshchei Khim., 1971, 41, 2486. S. T. McNeilly and J. A. Miller, J. Chem. SOC. (C) , 1971, 3007.

lD G. I. Drozd, M. A. Sokal'skii, and S. Z . Ivin, Zhur. obshchei Khim., 1970, 40, 701.

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Halogenophosphines and Related Compounds 53

A R' = OMc

Scheme 1

RPFz + X2 RPFzX2

( 7 ) R = Me or Ph

X = Cl or Br

Electrophilic Attack by Phosphorus. A detailed discussion has appeared of the displacement reactions of 1-chloro-2,2,3,4,4-pentamethylphosphetan (8) and its oxide and sulphide.20 The chloride (8) always undergoes inversion as a result of substitution at phosphorus, and this is rationalized on the basis of a transition state (9) in which the entering nucleophile (Nu) and the chloride leaving-group occupy apical sites. Although a pathway via (9)

( 9 ) + c1-

results in a considerable increase in ring-strain, over (8), alternative transition states are presumably even less favoured, owing to the necessary equatorial placement of at least one electronegative group [see (69), in Section 2, p. 651.

A series of papers on the reactions of chlorodimethylphosphine (10a) or fluorodimethylphosphine (1 Ob) with various nucleophiles has been pub- lished 21-24 and a summary is presented in Scheme 2. The low-temperature reactions of (loa) with methanol allowed the isolation of an intermediate salt (ll).23 The most complex reaction studied is that between (10a) and the oxide (12), in which attack at the phosphorus of (loa) by the oxygen of (12) is observed.22

ao J. R. Corfield, R. K. Okram, D. J. M. Smith, and S. Trippett,J. C. S. Perkin I, 1972,713. 21 F. Seel and K.-D. Velleman, Chem. Ber., 1971, 104, 2967. 22 F. Seel and K.-D. Velleman, Chem. Ber., 1971, 104, 2972. 23 F. Seel and K.-D. Velleman, Chem. Ber., 1972, 105, 406. 24 F. Seel, W. Gombler, and K.-D. Velleman, Annalen, 1972, 756, 181.

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54 Organophosphorus Chemistry

lA+ (10a) [ Me,PHOMe]+ Cl - - Me,P(O)H

Me,PX

Me,PZMe + Me,PF,H

Me,PPMe,

(a) X = C1 (b)X = F

(10)

0 H I I

Me,PCl + Me,P(O)E1 --+ Mc,POPMe, - -+ Mc,PH + Me,PCI

Me,P(O)CI + Me,P(O)H Me,P(O)OH + Me,PCI

Me,P( 0)Cl Me,PH

Simple displacement reactions leading to the cyanides (13),25 and to the phosphinothioites (14) 26 and (15) 27 have been described.

X Br I I

R-PSCH,CH=CH, Et PSR

(14) (15)

The reactions of phosphorus tri-iodide with ethers to give complex intermediates (1 6), which decompose to give tetraiododiphosphine and iodine, are controlled by the effect of steric and electronic factors in the ether upon the equilibria shown in Scheme 3.28 Ring-opening reactions

25 C. E. Jones and K. J. Coskran, Inorg. Chern., 1971, 10, 1536. 26 N. I. Rizpolozhenskii, V. D. Akamsin, and R. M. Eliseenkova, Izvest. Akad. Nuuk

S.S.S.R., Ser. khim., 1971, 198. 27 A. M. Potapov, E. A. Krasil'nikova, and A. I. Razumov, Zhur. obshchei Khirn., 1970,

40, 566. 28 N. G. Feshchenko, Zh. K. Gorbatemko, and A. V. Kirsanov, Zhur. obshchei Khim.,

1971, 41, 551.

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Halogenop h osp h ines and Related Compounds 55

L + -

K,O + PI3 R,OI PI, R,O + P,I, i- I,

Scheme 3 (16)

of oxetans with halogenophosphines continue to show interesting structure- reactivity effects. Thus 2-methyloxetan (1 7) with dichloro(pheny1)phosphine ring-opens predominantly at the primary carbon to give (18a) in 90% yield, whereas dichloro(NN-diethy1amino)phosphine gives 75% of (1 9b), by cleavage of the secondary carbon-oxygen bond of (17) (Scheme 4).29

C1 Me I I

R POC HCH,CH,CI (a) R = Ph (90%) (b) R = NEt, (25%) To CI,PR /' (c) R = CI (100%)

v \ Me

I

(17)

I R P OCH2CH,CHC1 (a) R = Ph (10%) (b) R = NEt, (75%)

(19) Scheme 4

Phosphorus trichloride is known to give only (18c) in its reaction with (17).30 With the epoxide (20) this trend is reversed (Scheme S), in that

CI Me I I

(a) R = CI

RPOCH,CHCl

(b) R = Ph (c) R = NEt,

RPCll

Me (21)

CI Me I I

(20)

R P 0 C H,C HC I (a) R = NEt,

(22)

&<

Scheme 5

2s 0. N. Nuretdinova, L. Z . Nikonova, and V. V. Pomazanov, Izvest. Akad. Nauk

9o B. A. Arbusov, L. Z . Nikonova, 0. N. Nuretdinova, and V. V. Pomazanov, Izuest. S.S.S.R., Ser. khim., 1971, 2225.

Akad. Nauk. S.S.S.R., Ser. khim., 1970, 1426.

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56 Organophosphorus Chemistry

phosphorus trichloride 31 and its phenyl analogue 29 cleave the secondary carbon-oxygen bond to give (21a, b), whereas the aminophosphine 30 gives comparable amounts of (21c) and (22a). At face value these results are difficult to rationalize, and it may be that some experimental factor, such as presence or absence of hydrogen chloride, plays an important role. Analogous studies with ethylene phosphorochloridite show that (1 7) 33

and (20) 32 react in the same mode (Scheme 6) , giving primary alkyl chloride products !

Scheme 6

Another controversial aspect of et her-halogenop hosp hine chemistry is the reactions of acetals or orthoformates with halogenophosphines. Russian workers have shown that the amide (23a) reacts sluggishly with orthoesters and not at all with acetals, whereas the dihalogenophosphine (23b) reacts vigorously with both types of compound (Scheme 7).34 These

L( Et

I

R 6 ‘CH(OEt), C1- + KbCH(OEt), II / bEt 0

+ E t a

RPOEt

(24)

+ EtCl + HC0,Et Scheme 7

31 N. I. Shuikin and I. F. Bel’skii, Zhur. obshchei Khim., 1959, 29, 2973. 32 A. N. Pudovik, E. M. Faizullin, and V. P. Zhukov, Zhur. obshchei Khim., 1966, 36,310. 33 0. N. Nuretdinov, B. A. Arbuzov, and L. Z. Nikonova, Izuest. Akad. Nauk S.S.S.R.,

Ser. khim., 1971, 2086. 34 V. S. Tsivunin, L. N. Krutskii, M. Ernazarov, and G. Kh. Kamai, Zhur. obshchei Khim.,

1970, 40,2560.

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Halog enop h osp h in es and Related Co mp o rinds 57

results imply that the initial role of the halogenophosphines is electrophilic, although in a previous study of these reactions, using various halogeno- phosphines, it was concluded that the phosphorus acts as a n~cleophi le .~~ The isolation of exchange products (24) from a number of these reactions 35

may be rationalized on either basis, as outlined for triethyl orthoformate. Treatment of santonin (25) and derivatives with phosphorus trichloride

or tribromide in the presence of acetic acid yields (Scheme 8) complex

CI ;C.r:-: +clq+ acetates

o 0 +

Scheme 8

mixtures of products in which the ketonic group has been removed, pre- sumably after interaction of the oxygen with the t r iha l ide~ .~~

A rationalization of the reactions between /I-keto-alcohols and halogeno- phosphines has been presented by a Russian In particular, the reaction between dichloro(pheny1)phosphine (26) and diacetone alcohol to give the oxide (27) has been shown to occur in stages (Scheme 9), and physical and chemical evidence has been presented for the initial formation of mesityl oxide (28) and the acid (29), followed by the addition product (30).37 A less detailed study of the analogous reaction of chlorodiphenyl- phosphine ( 5 ) with diacetone alcohol has also been published.3s

It has been suggested that the related reactions of saturated ketones with halogenophosphines have a similar pathway, and that the initial function of the halogenophosphine is to generate (3 1) by an aldol-type conden~at ion.~~

36 W. Dietsche, Annalen, 1968, 712, 21. 38 T. B. H. McMurray and D. F. Rane, J . Chem. SOC. (C), 1971, 3850. 37 B. A. Arbuzov, N. I. Rizpolozhenskii, A. 0. Vizel, K. H. Ivanovskaya, F. S. Muk-

hamentov, and E. I. Gol’dfarb, Zzvest. Akad. Nuuk S.S.S.R., Ser. khim., 1971, 117. 38 F. S. Mukhametov, N. I. Rizpolozhenskii, and E. I. Gol’dfarb, Zzvest. Akad. Nuuk

S.S.S.R., Ser. khim., 1971, 2221. s9 S. Kh. Nurtdinov, R. S. Khairullin, T. V. Burmakina, T. V. Zykova, R. Salakhutdinov,

V. S. Tsivunin, and G. Kh. Kamai, Zhur. obshchei Khim., 1971, 41, 1685.

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58 Organophosphorus Chemistry

OH 0 I II

PhPCI, + Mc,CCH,COMe --+ PhpH + Me,C=CHCOMe

0 Me II I (28) 11

PhP-CCH,COMe t-- PhPH I I I

OH 0 I I I

PhzPCl + Me,CCH,COMe --+ Ph2PCMe,CH,COMe

The usual product, after pyrolysis, is a 1,2-0xaphospholen 2-oxide (32), although an alcoholic work-up yields an acyclic phosphinate (33) (Scheme 10). Just in case these advances in our current mechanistic interpretation of these reactions (cf. ref. 40) leads to complacency, a further Russian paper has described the reactions of acetone and other simple ketones with chlorodiphenylphosphine or chlor~diethylphosphine.~~ These yield the a-chloroalkylphosphine oxide (34), or the derived oxide (39, and not the oxide (36), which is known42 to be formed from mesit yl oxide (2 8) and chlor odie thylp hosp hine. a-Halo genoal kylp hosp hine oxides are generally produced when aldehydes are heated with a wide range of halogenoph~sphines,~~ and the formation of such an adduct from a ketone is a novel result.

4 0 J. A. Miller in ‘Organophosphorus Chemistry’, ed. S. Trippett (Specialist Periodical Reports), The Chemical Society, 1972, vol. 3, pp. 44-45.

41 S. Kh. Nurtdinov, R. S. Khairullin, T. V. Zykova, V. S. Tsivunin, and G. Kh. Kamai, Zhur. obshchei Khim., 1971, 41, 2158.

42 T. V. Zykova, G. Kh. Nurtdinov, and G. Kh. Kamai, Zhur. obshchei Khim., 1967, 37, 692.

43 K. Sasse in ‘Organische Phosphorverbindung, Methoden der Organischen Chemie’, G. Thieme Verlag, Stuttgart, 1963, vol. 12 (l), pp. 155, 403.

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Halogenophosphines and Related Compounds

0 CI Me II I I

R'PCI, + MeCCH2R2 R1POCCHR2COMe I

CH2R2

(31)

0 Me

I \

:2$pMe - A R1PCCHR2COMe II I

CI CH2R2 R2 Me CH2R2

A ~ 3 0 ~ I (32)

0 Me II I

I \ R1PCCHR2COMe

R 3 0 CH2R2

(33) Scheme 10

0 c1 II I

Et2PCMe, i'

59

R2PCI + Me,C=O

\ 7 ,CH2 PhZPC,

Me (35)

0 I1

Et,PCI + Me,C=CHCOMe ___f Et,PCMe,CH,COMe (28) (36)

A number of aromatic substitution reactions of chlorophosphines have been reported. 1,3,5-Tri-t-butylbenzene gives the phosphinic chloride (37) 44 on treatment with aluminium trichloride, and not the phosphinous chloride (38).45 A simplified preparation of (39) has been de~cribed.*~

44

4b A. G. Cook, J . Org. Chem., 1965, 30, 1262. 46 I. Granoth, J. B. Levy, and C. Symmes, J . C. S. Perkin I& 1972, 697.

M. Yoshifuji, R. Okazaki, and N. Inamoto, J. C. S. Perkin I , 1972, 559.

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60 Organophosphorus Chemistry

o=P-Cl

t PCI

I I' I1

(30)

Biphilic Reactions with Dienes and with Unsaturated Curbonyl Com- pounds. The Diels-Alder reactions of the a/3-unsaturated lactone (40) have been de~cribed.~' The lactone is prepared by treatment of chloro- methyldichlorophosphine (41) with propiolic acid and then hot acetic

0

EtO\ EtS\ EtOl ' EtS(

x = Cll Rates:

anhydride.47 The ease of addition of halogenophosphines to 1,3-dienes is found to decrease in the sequence outlined for buta-l,3-diene (42).48

Miscellaneous. Boron tribromide treatment of dichloro(pheny1)- phosphine (26) gives the dibromide quantitati~ely.~~ Phenyl radicals and

47 V. K. Khairullin, G. V. Dmitrieva, and A. N. Pudovik, Izuest. Akad. Nauk S.S.S.R., Ser. khim., 1971, 1254.

O8 L. I. Zubstova, N. A. Razumova, and A. A. Petrov, Zhur. obshchei Khim., 1971, 41, 2428.

49 P. M. Druce and M. F. Lappert, J. Chetn. SOC. ( A ) , 1971, 3595.

= Et ,

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Halogenophosphines and Related Compounds 61

PhPCI, + BBr, ----+ PhPBr,

(26)

t-butyl radicals react with phosphorus trichloride to give dichloro- phosphine~.~~ Radiolysis of olefins in the presence of phosphorus trichloride gives the dichlorophosphines (43).61 The oxidative addition of phosphorus trichloride to vinyl chloride has been shown to yield a mixture of the phosphate (44) and the phosphonate (45),62 and not a mixture of (45)

c1 60Co 1

R'CH=CHR2 + PCI3 R'CH=CHR2PCI,

(43a) +

CI 1

R2CH=CHR1PCl,

(43b)

0 0 II II

CI,PCHCICH,Cl + Cl,POCHClCH2CI y (45) (44)

CH2=CHCI + PCI,

CI,PCH2CHCl,

(46)

and (46).53 Bis(trifluoromethy1)fluorophosphine (47) is oxidized to the corresponding oxide with nitric

It is likely that the reaction of bis(chloromethy1)chlorophosphine with benzaldehyde in wet dioxan to produce the oxide (48) involves the initial hydrolysis of the phosphine, to give (49), which adds to benzaldehyde (Scheme 1 l).55

L. Dulog, F. Nierlich, and A. Verhelst, Chem. Ber., 1972, 105, 1971.

2171. C. B. C. Boyce and S. B. Webb, J. Chem. SOC. (C) , 1971, 3987.

63 W. M. Daniewski, M. Gordon, and C. E. Griffin, J. Org. Chem., 1966,31, 2083. s4 R. C. Dobbie, J. Chem. SOC. (A) , 1971,2894. 6s N. I. D'yakonova, E. Kh, Mukhametzyanova, and I. M. Shermergorn, Zhur. obshchei

Khim., 1971, 41, 2203.

b1 P. A. Zagorets, A. G. Shostenko, and A. M. Dodonov, Zhur. obshchei Khim., 1971'41,

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62 Organophosphorus Chemistry

0 OH II I

wet dioxan

(CICH,),PCI + PhCH=O - (CICH,),PCHPh ";1 (48)

(CICH,),PH 0 I t + HCI I PhCH=O

(49) Scheme 11

2 Halogenophosphoranes

Preparation and Structure.-Two new routes to the relatively rare tetra-alkylfluorophosphoranes (50) from salt-free ylides have been r e p ~ r t e d . ~ ~ These phosphoranes all have considerable 'fluoride' character (no HCPF coupling), although the tributyl derivative (50; R = Bu) is quite stable and definitely monomeric. Difluorophosphorane (5 1) has been prepared from excess hydrogen fluoride and diphosphine, and found to disproportionate readily to trifluorophosphorane (52).57 The infrared spectrum of (51) indicates symmetry, which is accounted for by a

H F H F R3P=CHZ ---+ R,P(F)Me f------ R,P=CHSiMe3

(50)

(PHZ), + HF PHZF + PH3.

H3PFZ H2PF3 + PH3 + HF

(51) (52)

> 0 ° C RPF2 + XZ -----+ RPFzXz RPF,

R = Ph or Me X = Br or C1

- 196°C PF, + FCI PCIF4

( 5 5 )

(54)

56 H. Schmidbaur, K.-H. Mitschke, and J. Weidlein, Angew. Chem. Internat. Edn., 1972, 11, 144.

57 F. See1 and K. Velleman, 2. anorg. Chem., 1971, 385, 123.

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Halogenophosphines and Related Compounds 63

trigonal-bipyramidal structure, with axial fluorines. The addition of chlorine or bromine to difluorophosphines yields the mixed halogeno- phosphoranes (53), but these disproportionate readily to give (54).1° A related reaction leads to improved yields of chlorotetrafluorophosphine ( 5 3 , provided the vacuum temperature is kept very low.68

Perfluoro-t-butyl hypochlorite has been used to prepare the phosphoranes (56),6D in which the fluorines are equivalent (from n.m.r.) at room tempera- ture. The exchange with aryloxysilanes to give (57) appears to be general and quantitative.60 Detailed l9F and 31P n.m.r. data on (57) have been

Rn I

RnPF5-, + ArOSiMe3 * (ArO),-,PF, (57) 11 = 0, 1, or 2

+ RPF4 fJO\T /m &::::I 0 (58)

presented, and earlier work 61 in this area questioned.60 Related reactions have been used to prepare the phosphoranes (58), and the variable- temperature n.m.r. spectra analysed.62

Aminotetrafluorophosphorane (59) has been prepared from ammonia, and a detailed analysis of the n.m.r. data (lH, I9F, and 31P) indicates that it has a trigonal-bipyramidal structure, in which the equatorial nitrogen has a planar config~ration.~~ The axial fluorines (JPF 760 Hz) are chemically equivalent, but show different coupling to the hydrogens, while the equa- torial fluorines (Jpp 936 Hz) are equivalent in both respects. This has been interpreted on the basis of the amino-hydrogens lying in an axial plane, as in (59), with resultant strong hydrogen-bonding to the axial fluorines. Variable-temperature n.m.r. studies have revealed a high barrier to rotation

F

Me,NPF4

W. B. Fox, D. E. Young, R. Foester, and K. Cohn, Znorg. Nuclear Chem. Letters, 1971, 7 , 861. D. E. Young and W. B. Fox, Inorg. Nuclear Chem. Letters, 1971, 7 , 1033.

Bo S. C. Peake, M. Fild, M. J. C. Hewson, and R. Schmutzler, Znorg. Chem., 1971,10,2723. R. A. Mitsch, J. Amer. Chem. SOC., 1967, 89, 6297.

62 M. Eisenhut and R. Schmutzler, Chem. Comm., 1971, 1452. 83 A. H. Cowley and J. R. Schweiger, J . C. S. Chem. Comm., 1972, 560.

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64 Organophosphorus Chemistry

[above 15 kcal mol-l, compared with 9 kcal mol-1 for the dimethylamino- analogue (60)] 64 which has been ascribed to this intramolecular hydrogen- bonding.63 N-Methylaminotetrafluorophosphorane (61) has now been prepared by the silane route, and found to give three 19F resonances at - 80 "C, presumably owing to hindered rotation.65 A similar route to the piperidyl derivatives (62) has been described, and the dependence of the non-equivalence of the fluorines upon the position of the methyl group

Me,SiNHMe -t PF, - Me,SiF + MeNHPF,

(61)

SiMe, Fbi.-,L,PPh,

(62) IZ = 0, 1, or 2

r7 n X N-I'FZXZ + SbF3 - X N-PF, W W

(63) X = CH, or 0

PhN=P(NEt,)Cl, -1 SbF3 A Et,NPF.j

(64)

has been rationalized on the same basis.66 Unsubstituted piperidyl- and morpholino-phosphoranes (63) have been prepared by the antimony trifluoride exchange and the same reagent has been used in a more unusual exchange involving the iminophosphorane (64).68

An elegant and stimulating MO analysis of the problems of bonding and structure in phosphoranes has appeared.69 Of particular relevance to the current topic is a discussion of the interactions of the lone pairs of donor substituents with the orbitals on phosphorus. The authors conclude that donor substituents will prefer equatorial sites (except where electro- negativity becomes the dominating influence, as with fluorine), and more- over, that the highest occupied donor orbital will prefer to lie in the equa- torial plane of the phosphorane, rather than in the axial plane, i.e. (65) is preferred over (66). Although only limited experimental data are available, it would appear that these predictions are fully supported, e.g. the preferred conformation of (67) 70 and the features of the phosphoranes (59) and (61),

64 G . M. Whitesides and H. L. Mitchell, J. Amer. Chem. SOC., 1969, 91, 5384. 66 J. S. Harman and D . W. A. Sharp, Znorg. Chem., 1971, 10, 1538. 66 M. J. C. Hewson, S. C. Peake, and R. Schmutzler, Chem. Comm., 1971, 1454. 67 G. I. Drozd, M. A. Sokal'skii, 0. G. Strukov, and S. Z. Ivin, Zhur. obshchei Khim.,

1970,40, 2396. 68 M. Bermann and J. R. Van Wazer, Angew. Chem. Internat. Edn., 1971, 10, 733. 69 R. Hoffmann, J. M. Howell, and E. L. Muetterties, J. Amer. Chem. SOC., 1972,94,3047. 7 0 S. C. Peake and R. Schmutzler, J . Chern. Soc. (A) , 1970, 1049.

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Halogenophosphines and Related Compounds 65

i65) (66) (47)

discussed above. Thus the hindered rotation observed in the aminophos- phoranes can be explained on the basis of orbital interactions, and it remains to be seen how important any hydrogen-bonding interactions are in relation to this.

Bis(trifluoromethy1) peroxide and disulphide have been used in a novel preparation of the difluorophosphoranes (68) from tertiary pho~phines .~~ The phosphetan derivative (69), prepared by this route, has been shown to exist as a mixture of two isomers at -1OO"C, one of which has a

X = O o r S (CF3X)z + R3P R,PF,

( 4 8 )

I I = 1, 2, or 3

diequatorial heterocyclic ring.71 Boron trifluoride catalyses the exchange of ligands in the phosphorane (70).72

Reactions.-An intermediate (7 1) has been isolated from the bromina- tion of alcohols using triphenylphosphine dibromide in dimethylformamide (Scheme 12).73 This implies that these reactions are closely related to the Vilsmeier reaction, and further evidence for this view comes from the isolation of a formylated product (72) from the analogous reaction of cholest-5-ene-3/3,4/3-diol (73).74 The other product (74) appears to be the result of an enol-bromination of the 3-ket0ne.~~ Two related reactions which substantiate this are the mild reaction between pentane-2,4-dione and triphenylphosphine dibromide in DMF, to give (75),75 and the forma- tion of l-chlorocyclohex-l-ene (76) from cyclohexanone and a solution of

71 N. J. De'ath, D. Z. Denney, and D. €3. Denney, J. C. S. Chem. Comm., 1972, 272. 72 H. Binder, 2. anorg. Chem., 1971, 384, 193. 73 M. E. Herr and R. A. Johnson, J. Org. Chem., 1972, 37, 310. 14 J. Dahl, and R. Stevenson, and N. S. Bhacca, J . Org. Chem., 1971, 36, 3243. 76 J. Carnduff, J. Larkin, J. A. Miller, D. C. Nonhebel, B. R. Stockdale, and H. C. S. Wood.

J . C. S. Perkin I , 1972, 692.

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66 Organophosphorus Chemistry

OR =

-

+ Me,NCH=O + Ph,PBr, Me,N=CHOPPh,Br

+ RoHll Me,N=CHOR + Ph,P=O t--- Me,N-yHOPPh,Br

OR

MeNCOPh

,o H , . @ Scheme 12

triphenylphosphine in carbon tetra~hloride.'~ Thus the conversion of ketones into halogeno-olefins appears to be a promising synthetic reaction of halogenophosphoranes, or their phosphonium relatives, although

I

OH (73) + 2\

OHCW

(72)

0 0 0 I1 II D M F II

MeCCH,CMe + Ph,PBr, - MeCCH=C(Br)Me

(75)

0 II

/c\ Ph,P-CCI, CH, CH, Ph,P-CCI,

'(CH,),, 6 ) n = 2 ' I 1 = 3 o x (76) (77)

7 6 N. S. Isaacs and D. Kirkpatrick, J. C. S. Chem. Comm., 1972, 443.

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Halogenophosphines and Related Compounds 67

competing pathways clearly exist, as in the reaction of cyclopentanone to give (77).76

The formation of equal amounts of methyl chloride and (78) from phosphorus pentachloride and bis(hydroxymethy1)phosphinic acid has been rationalized (Scheme 13) in terms of the intermediate methyl ester (79).77

OH I

/ \

0 II

(HOCH2)POH + PCl, - CliPOP-CH2OH + HCI

O-CH2

1 0 II 0

II ClCH2PC12 + CH3Cl t---- C14P0P0CH3 I

(78) CH20H

(79) Scheme 13

A slightly modified version of this rationalization is presented below. Diols can be converted into oxirans via the corresponding acetals, which fragment via the orthoester derivatives (80) on treatment with phosphorus pentachloride (Scheme 14).78 The sequence is primarily of interest because

Scheme 14

of its stereospecificity, since the final oxiran has the same absolute con- figuration at carbon as the initial diol, in appropriate cases.

Ethers and certain sulphides are cleaved by triphenylphosphine dibromide to give alkyl bromides (Scheme 15), although the reaction is not general

77 Yu. V. Nazarov, A. A. Muslinkin, and V. F. Zmeltukhin, Izvest. Akad. Nauk S.S.S.R., Ser. khim., 1971, 1806. M. S. Newman and C. H. Chen, J. Amer. Chem. SOC., 1972,94,2149.

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68 Organophosphorus Chemistry

R 1 0 R 2 + Ph,PBr2 - R2Br + RlBr + Ph3P=0

Scheme 15

for epoxides, as shown by the reactions yielding (81) and (82), and (83).7s Alkyl iodides result from a similar reaction of the phosphorane (84) with alcohols or ethers such as tetrahydrofuran.*O Further examples of the preparation of vinylphosphonate derivatives from ethers and phosphorus

Ph3PBr2 + 0 --+ 0- + i- aBr OPPh3

Br Br Ph,PBr, 4-

4Me- Me

CI (88)

79 A. G. Anderson and F. J. Freenor, J. Org. Chem., 1972, 37, 626. N. G. Feshchenko, I. K. Mazepa, S. I. Shila, and A. V. Kirsanov, Zhur. obshchei Khim., 1971, 41,2375.

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Halogenophosphines and Related Compounds 69

pentachloride are the reactions leading to (85) 81 and (86).829 83 The contrast between (80) and 2-methyl-1,3-dioxolone (87) is clearly related to the ease of fragmentation of (80) to give chloride ion. Since a previous study of the reaction leading to (85) has described the formation of 1,4-dichlorobutane (88) [cf. (84) 3, the reaction conditions would appear to be critical.84

The exchange reactions between fluorophosphoranes and silane derivatives have been utilized for the fluorination of alcohols, via their trimethylsilyl ethers (89).85, 86 According to one of these reports, the alkyl fluoride is generally accompanied by ~ l e f i n . ~ ~ Phosphorus penta- fluoride similarly fluorinates siloxanes such as (90).87

ROSiMe3 + PhPF4 --+ R F + PhP(O)F, + FSiMe, (89)

Further examples of the preparation of phosphonates from acetals and phosphorus pentachloride include those leading to (91) 8 8 s and (92).90 The reaction of phosphorus pentachloride with t-butanol yields the phosphonate (93), which eliminates hydrogen chloride on treatment with base.Ol The phosphorus-carbon bond-forming steps of the reactions leading to (91)-(93) appear to involve the addition of phosphorus pentachloride to electron-rich olefins.

81

82

83

84

86

86

87

88

89

90

91

S. V. Fridland, G. Kh. Kamai, L. V. Voloboeva, Zhur. obshchei Khim., 1970,40, 595. S . V. Fridland, S. K. Chirkunova, V. A. Kataeva, and G. Kh. Kamai, Zhur. obschchei Khim., 1971, 41, 554. S. V. Fridland, T. V. Zykova, S. K. Chirkunova, V. A. Kataeva, and G. Kh. Kamai, Zhur. obshchei Khim., 1971, 41, 1041. N. I. Shuikin, I. F. Bel'skii, and I. E. Grushko, Izoest. Akad. Nauk S.S.S.R., Otdel. Khim. Nauk, 1963, 557. D. U. Robert and J. G. Reiss, Tetrahedron Letters, 1972, 847. H. Koop and R. Schmutzler, J. Fluorine Chem., 1971, 1, 252. E. W. Kifer and C. H. Van-Dyke, Inorg. Chem., 1972,11,404. V. V. Moskva, G. F. Nazvanoya, T. V. Zykova, and A. I. Razumov, Zhur. obshchei Khim., 1971, 41, 1489. V. V. Moskva, G. F. Nazvanoya, T. V. Zykova, and A. I. Razumov, Zhur. obshchei Khim., 1971,41, 1493. V. V. Moskva, L. A. Bashirova, T. V. Zykova, and A. I. Razumov, Zhur. obshchei Khim., 1970, 40, 2764. V. V. Moskva, L. A. Bashirova, and A. I. Razumov, Zhur. obshchei Khim., 1971, 41, 2577.

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70 Organophosphorus Chemistry

0 so, II

CH,=CHCH(OEt), + Pc15 + CI,PC=CH(OEt) I

(92)

CH,CI

0 CI i benzene 11 I

PCI5 + Me3COH Cl,PCH,CMe,

(93)

0 I I

CI,P CH=C Me,

Salts are produced by the reaction of fluorophosphoranes with N-silylimines (94).O2. 93 Vinyl isocyanate reacts with phosphorus penta- chloride to give a hexachlorophosphate salt (93, which yields the phosphonic dichloride (96) on hydrolysis and di~ti l lation.~~ Butyl cyanate reacts with phosphorus pentachloride to give two products, (97) and (98).s5

Me3SiN=PR3 + Me,PF3 --+ [Me,PF,l- [Me,P(N=PK,),l+

(94)

CHz=CHoN=C=O + PCI, - [CI,PCH=CHNHCOCll+ P a 6 -

(95)

i , SO, i i , A

+ CldP-N=C=O + RCl

O2 W. Stadelmann, 0. Stelzer, and R. Schmutzler, Chem. Comm., 1971, 1456. O3 W. Stadelmann, 0. Stelzer and R. Schmutzler, 2. anorg. Chem., 1971, 385, 142. O 4 V. V. Doroshenko, E. A. Stukalo, and A. V. Kirsanov, Zhur. obshchei Khim., 1971,41,

1645. s6 N. K. Kulibaba, V. I. Shevchenko, and A. V. Kirsanov, Zhur. obshchei Khim., 1971,

41, 2105.

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Halogenophosphines and Related Compounds 71

3 Phosphines containing a P-X Bond (X = Si, Ge, or Sn)

Mislow’s group has continued to study inversion barriers in phosphines and arsines, and test the generality of the theoryQ6 that barrier height is controlled by the electronegativity of the ligands. For example, the barrier in (99) is 18 kcal mol-1 less than that in (loo), and the difference was explained on this basis.Q7 The trimethoxysilylphosphine (101 a) has a barrier 2 kcal mol-1 less than that of the trimethylsilylphosphine (1 01 b),Q8

L4CPh SiMe3 Me

(99) (100)

+)- 6 M e

‘Si(0Me)a Ph-P,

A Ph-P,

SR3

(a)R = OMe (b)R = Me

(101)

contrary to the predictions of the above theory,Qs and negative hyper- conjugation [implying a contribution from (102) to the ground state of (101a) ] has been suggested as an explana t i~n .~~

The synthesis and uses of alkali-metal tetraphosphinoaluminates (1 03) continue to be of interest,O@ and further examples of the synthesis of silyl- phosphines have appeared.loo Phenyl(trimethy1silyl)phosphine (104) has

XSiR2,R3, - MAI(PHR1)4 - R1HP.SiR2, R33--n

(103) M = Na or Li R1 = H or Me R1 = R3 = H, R2 = M e f o r n = 0, I , or 2

R1 = R2 = Me, R3 = H for n = 0-3

PhPHK + MesSiCI PhPHSiMe3 (104) -

been prepared.lol A new synthesis of silylphosphine involves heating a mixture of phosphine and silane at 300 OC.lo2

The silicon-phosphorus bond of dimethyl(trimethylsily1)phosphine (105) is readily cleaved by a variety of covalent halides, as shown in Scheme 16.1°3 Further examples of insertion by carbon multiple bonds

g6 R. D. Baechler and K. Mislow, J. Amer. Chem. Soc., 1971, 93, 773. R. D. Baechler, J. P. Casey, R. J. Cook, G. H. Senkler, and K. Mislow, J. Amer. Chem. SOC., 1972, 94, 2859.

Bs R. D. Baechler and K. Mislow, J. C. S . Chem. Comm., 1972, 185. J. A. Miller, in ‘Organophosphorus Chemistry’ ed. S. Trippett (Specialist Periodical Reports), The Chemical Society, 1971, vol. 2, p. 52; 1972, vol. 3, p. 53.

loo G. Fritz and H. Schafer, Z. anorg. Chem., 1971, 385, 243. lol M. Baudler and A. Zarkadas, Chem. Ber., 1971, 104, 3519. lo2 I. H. Sabherwal, and A. B. Burg, Inorg. Nuclear Chem. Letters, 1972, 8, 27. loS J. E. Byrne and C. R. RUSS, J. Organometallic Chem., 1972, 38, 319.

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72 Organophosphorus Chemistry

SlCl,

CEiI

SO,CI,

Me3SiCI + Me,PSiCI,

Me3SiI + Me,PCF3 I- MesSiCl + Me,PS02CI

Mc,PSiMe !,

(105)

J.

Me,P(O)CI + SO,

Scheme 16

into germylphosphines have appeared, and confirm the trends previously established.lo4e lo5 These are illustrated in Scheme 17 for the trialklygermyl-

OMe I I I

> MeCCOGeMe3 I PEt,

(MeCO),

R = Me

CH,=CHCN

R = E t Et,PCH,CH(CN) GeEt, R,GePEt,

( I 06)

MeCO,CH= CH,

R = Me > Me3GeOCH=CH2

Me COP Et, +

Scheme 17

diethylphosphines (106). The n.m.r. spectra of a number of phenylphosphines of general formula (107) have been studied, and 31P shifts,lo6 JPH values,1o7 and Jpsn values lo* measured,

R,MPHPh

M = Si, Ge, or Sn R = Me or Ph

( 107)

lo4 J. Satgd, C. Couret, and J. Escudie, J. Organometallic Chem., 1971, 30, C70. lo5 J. Satgd, C. Couret, and J. Escudie, J. Organometallic Chem., 1972, 34, 83. lo6 G. Engelhardt, 2. anorg. Chem., 1972, 387, 52. lo' D. G. Harrison, S. E. Ulrich, and J. J. Zuckermann, Inorg. Chem., 1972, 11, 25. lo8 W. B. Fox, D. E. Young, R. Foester, and K. Cohn, Inorg. Nuclear Chem. Letters,

1971, 7, 865.

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