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Inorganica Chimica Acta 358 (2005) 1719–1723

Note

Phosphonato-phosphinito peri-substituted naphthalenes

Petr Kilian, Alexandra M.Z. Slawin, J. Derek Woollins *

School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, UK

Received 17 June 2004; accepted 9 September 2004

Available online 7 October 2004

Dedicated to Professor F.G.A. Stone, in recognition of his towering contribution to inorganic chemistry

Abstract

Nap[P(E)(OMe)2][P(H)(O)(OMe)] (Nap = naphthalene-1,8-diyl, E = S, Se) were synthesized and fully characterised including

crystal structure analyses. They show repulsive interactions of phosphorus functionalities with hydrogen atom of phosphinite moiety

placed in the peri space, the distortion of naphthalene backbone is comparable to that observed in 1,8-bis(phosphonato) naphtha-

lenes. The conformational isomerism resulting from the restriction of the cogwheel rotational motion about the C–P bonds is

observable by NMR.

� 2004 Elsevier B.V. All rights reserved.

Keywords: Organophosphorus; Strained molecules; Peri-interactions; Phosphorous; Steric crowding; Synthesis; X-ray structure

1. Introduction

Recent interest in the chemistry and structure of

peri-substituted naphthalenes stems from their unusual

peri-region bonding geometry, imposed by the stiff

naphthalene-1,8-diyl backbone [1–5]. We have per-

formed a comparative synthetic and characterizationstudy of a series of 1,8-bis(dimethyl phosphonito)

naphthalenes and their congeners, the series included

phosphonato-phosphonites 1 and 2 [6]. These served

as precursors for phosphonato-phosphinite esters 3

and 4, whose syntheses and full characterization

including X-ray structure determinations are reported

here. The presence of reactive P–H bond in the primary

phosphinic esters 3 and 4 makes them potentialsynthons.

The ester 4 was obtained as a major product on at-

tempts to purify selenated derivative 2 by flash chroma-

0020-1693/$ - see front matter � 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.ica.2004.09.019

* Corresponding author. Tel.: +44 1334 463861; fax: +44 1334

463384.

E-mail address: jdw3@st-and.ac.uk (J.D. Woollins).

tography on silica. We expected the mechanism of such

a transformation to involve hydrolytical cleavage of

phosphonite ester, followed by tautomeric change to tet-

rahedral phosphinite (Scheme 1). To verify this hypoth-

esis we hydrolysed the phosphonito derivatives 1 and 2

in THF as a solvent, which gave phosphonato-phosphi-

nite esters 3 and 4, respectively, in good yields, confirm-ing the proposed reaction sequence. The hydrolysis of

phosphonites is known to be rapid in acid media and

slow under neutral or basic conditions [7], in our case

a complete conversion to 3 and 4, respectively, was ob-

served by 31P NMR after 24 h without any acid

catalysis.

As expected, the 31P{1H} NMR spectrum of 4 is a

simple AX system with very small magnitude of 4J(PP)2.2 Hz. 1 Interestingly, the 31P{1H} spectrum of sulfur

congener 3 (D8-toluene, 109.4 MHz, 25 �C) shows a

more complicated pattern. Thus the higher-frequency

1 The high frequency signal has a symmetric set of 77Se satellites,1J(PSe) = 875 Hz.

Table 1

Crystallographic data for 3 and 4

Compound 3 4

Formula C13H16O4P2S C13H16O4P2Se

Crystal habit colourless prism colourless prism

Crystal system triclinic monoclinic

Space group P�1 P2(1)/c

Unit cell dimensions

a (A) 9.830(1) 12.933(2)

b (A) 12.261(1) 11.446(2)

c (A) 13.093(2) 10.645(2)

a (�) 78.719(2) 90.00

b (�) 78.684(2) 106.362(3)

c (�) 72.660(2) 90.00

Z 4 4

R (F2 all data) 0.0481 0.0298

wR (F2 all data) 0.1031 0.0644

PP

E

1 E = S2 E = Se

POMe MeO

MeOE

POHOMe

OMe

H2O

-MeOH

PMeO

E

PHOMe

O

3 E = S4 E = Se

MeOMeO

MeO

Scheme 1.

1720 P. Kilian et al. / Inorganica Chimica Acta 358 (2005) 1719–1723

signal consists of a doublet at d 91.2 [P1; 4J(PP)1.7 Hz

was read from spectra]; however the low-frequency sig-

nal (d 25.2, P9) is an unresolved multiplet, probably aris-

ing from superposition of several doublets with small

magnitude of 4J(PP). We ascribe this NMR behavior

to hindered cogwheel-like rotation of the phosphorus

functionalities about the P–C bonds, giving rise to sev-eral rotamers observable on the NMR time scale. In-

deed, similar NMR behavior was observed in

phosphine oxide Nap(POCl2)(PCl2) [8] and phospho-

nium salts Nap(PPh2)(PRPh2)+ (R = Me, benzyl) [9].

Poor resolution of signals of rotamers 3 at temperatures

studied (188–373 K) prevented quantitative analysis of

the system. The signal of proton directly bonded to

phosphorus in 1H NMR spectra appears as doublet cen-tered at d 8.69 (in 3) and 8.76 (in 4), the magnitudes of1J(HP) found (616 and 613 Hz) are as expected for a

pentavalent phosphorus environment. The diastereo-

topic methoxy groups of phosphonate moiety in both

3 and 4 are anisochronous in both 1H and 13C NMR

spectra. We observed some changes of 1H chemical

shifts of these in a variable temperature study, however

even at 373 K the system was still far from coalescencetemperature.

Fig. 1. One of the two independent molecules in asymmetric unit of 3

in the crystal. Naphthalene H atoms are omitted for clarity. Selected

bond lengths (A) and angles (�): P(1)–C(1) 1.813(3) [1.824(3)], P(9)–C(9) 1.804(3) [1.819(3)], P(1)–S(1) 1.936(1) [1.924(1)], P(9)–O(9)

1.477(2) [1.480(2)], the P(9)–H(9) distance was set to 1.25A ; P(1)–

C(1)–C(10) 126.8(2) [124.9(2)], P(9)–C(9)–C(10) 126.1(2) [128.5(2)],

C(1)–C(10)–C(9) 126.7(3) [127.5(3)]. Values in square brackets are for

second independent molecule in asymmetric unit.

Compound 3 crystallizes with two independent mole-

cules of similar geometry in the asymmetric unit (Figs. 1

and 3, Table 1). It displays twisted naphthalene geome-

try, resulting from clearly repulsive interaction between

the phosphorus functionalities. The P� � �P nonbonding

distance of 3.57 A (3.53 A in the second independent

molecule) found in 3 is significantly longer than that ob-

served in the parent compound 1 (3.31 A) and compara-ble to that observed in Nap[P(S)(OMe)2][P(O)(OMe)2]

(3.59 A) [6]. The displacements of P atoms from the

mean naphthalene plane were quite different for the

two independent molecules in the asymmetric unit

(0.75 and �0.93 vs. 0.71 and �0.72 A), also the P(1)–

C(1)� � �C(9)–P(9) dihedral angles were relatively different[42.9� and 36.5�] in the two independent molecules,

although very similar splay angles 2 19.6� and 20.9� wereobserved. The molecules adopt the conformation with

the burden of the peri-region strain accepted by

H(9)� � �S(1), H(9)� � �P(1) and P(1)� � �P(9) contacts, thesereaching 92–94% of their respective sum of Van der

Waals radii. 3 There is no conformation dictating attrac-

tive 3c–4e interaction as indicated by the non-linear

arrangements of atoms [e.g., P(9)–H(9)� � �S(1) angle is

129�] [10].The geometry of the molecule 4 in the crystal (Figs. 2

and 3, Table 1) is also defined by the repulsive interac-

tion of its peri-substituents, the nonbonding P� � �P dis-

tance in 4 is 3.52 A (93% of 2 · rVdW). Despite only

moderate atom size increase on transition from sulfur

to selenium there are significant changes in the geome-

tries of 3 and 4. The differences in alignment of the

peri-substituents in 3 and 4 are illustrated in Fig. 3. Fur-thermore, the molecule of 4 shows less out-of-plane dis-

2 Splay angle = [P(1)–C(1)–C(10)] + [P(9)–C(9)–C(1)] + [C(1)–

C(10)–C(9)] – 360.3 Following values of Van der Waals radii were used in calculations:

rVdW(P) = 1.90, rVdW(O) = 1.52, rVdW(S) = 1.80, rVdW(Se) = 1.90,

rVdW(H) = 1.20 A.

PMeO

Se

PHOMe

OMeO P

MeOP

OMeSe O

- MeOH

Scheme 2.

Fig. 3. The molecules of 3 and 4 viewed approximately along the

central C(10)–C(5) bond to illustrate the extent of naphthalene ring

twisting, out-of-plane and in-plane displacements of phosphorus

functionalities and their mutual orientation.

Fig. 2. The molecule of 4 in the crystal. Naphthalene H atoms are

omitted for clarity. Selected bond lengths (A) and angles (�): P(1)–C(1)1.809(2), P(9)–C(9) 1.812(2), P(1)–Se(1) 2.0841(7), P(9)–O(9) 1.457(2),

the P(9)–H(9) distance was set to 1.25A; P(1)–C(1)–C(10) 127.3(2),

P(9)–C(9)–C(10) 130.8(2), C(1)–C(10)–C(9) 127.7(2).

P. Kilian et al. / Inorganica Chimica Acta 358 (2005) 1719–1723 1721

tortion than molecule 3, to balance this there is more

crowding (sub Van der Waals contacts) in the peri-

region and more pronounced in-plane distortion in 4.

Thus in 4 the distances of phosphorus atoms from the

naphthalene mean plane are 0.37 [P(1)] and 0.65 A

[P(9)]; the P(1)–C(1)� � �C(9)–P(9) dihedral angle is

24.2(1)� and the splay angle is widened to 25.8�. Thesub Van der Waals contacts are displayed by all atoms

facing the H(9) atom e.g., O(11), P(1) and Se(1), theseX� � �H contacts reach 88–92% of

PrVdW, very short is

also O(11)� � �P(9) contact (86% ofP

rVdW). Despite

these short contacts, O(11), P(9) or any other atoms in

4 are not involved in any approximate linear arrange-

ment for possible 3c–4e interaction.

In short, we have shown that the phosphinite func-

tionality in 3 and 4 aligns with the hydrogen atom bear-

ing the burden of the steric strain, the distortions ofnaphthalene backbone are comparable to other conge-

ners with tetrahedral phosphorus geometry such as

bis(phosphonates).

The MS (EI+, 70 eV) spectra revealed the tendency

of 4 towards the cyclisation, accomplished by elimina-

tion of MeOH. Whilst at probe temperature of 180 �Cthe base peak at m/z 299 (M–Se + H) was observed, at

higher temperature (250 �C) the spectrum was domi-nated by peak at m/z 346, probably stemming from

bridged product after elimination of methanol

(Scheme 2).

Contrary to 4, the base peak in EI-MS spectrum of 3

is assignable to C10H6PS(OMe)2 fragment – a product of

P–C bond breakage, relaxing the crowding in the peri-

region of naphthalene.

2. Experimental

2.1. Preparation and characterisation of 3

The solution of 1 (0.17 g, 0.49 mmol) in THF (5 cm3)

and water (0.05 cm3, excess) was stirred for 24 h and the

volatiles were evaporated in vacuo. Resulting oil wasdissolved in hot hexane/toluene, which after cooling af-

forded pure 3 as colourless crystals. Yield 0.13 g (80%).

M.p. 103–105 �C. C13H16O4P2S: Calc. C, 47.3; H, 4.9.

Found: C, 47.7; H, 4.8%. Crystals for X-ray work were

obtained from hexane/toluene. IR (KBr tablet, cm�1):

m = 3052, 2998w (mAr–H), 2946m, 2840w (mC–H), 2440w(mP–H), 1493m, 1232, 1221 (mP@O), 1195s, 1042 and

1017vs (m(P)–O–C), 811vs, 791vs, 774m (mP–O–(C)), 664s,632s, 446s. Ra (sealed capillary, cm�1): m = 3070m,

1722 P. Kilian et al. / Inorganica Chimica Acta 358 (2005) 1719–1723

3051s (mAr–H), 2949m, 2842w (mC–H), 2444m (mP–H),1554vs, 1328vs, 927m, 891m, 557vs. NMR (CDCl3,

298K): 1H (300 MHz): d = 3.46 [d, 3H, 3J(HP) = 12.3

Hz, H12], 3.64 and 3.79 [2 · d, 2 · 3H, 3J(HP) = 13.6

Hz, H11], 7.48–7.59 [m (complex), 2H, H3 and H7],

7.94–8.01 [m (complex), 2H, H4 and H6], 8.28 [ddd,1H, 3J(HH) = 7.3, 4J(HH) = 1.4, 3J(HP) = 19.3 Hz,

H2], 8.46 [ddd, 1H, 3J(HH) = 7.2, 4J(HH) = 1.4,3J(HP) = 15.1 Hz, H8], 8.69 [d, 1H, 1J(HP) = 616 Hz,

H9]; 13C{1H} (75.5 MHz): d = 52.6 [d, 2J(CP) = 6.1

Hz, C12], 53.6 [d, 2J(CP) = 6.6 Hz, C11], 54.2 [d,2J(CP) = 7.2 Hz, C11], 125.3 [d, 3J(CP) = 17.1 Hz, C3],

125.6 [d, 3J(CP) = 12.7, C7], 129.0 [dd, 1J(CP) = 148.2,3J(CP) = 2.8 Hz, C1], 129.4 [dd, 1J(CP) = 129.4,3J(CP) = 2.8 Hz, C9], 130.7 [dd, 3J(CP) = 11.1 and

10.0 Hz, C5], 134.7 [dd, 2J(CP) = 12.2 and 10.5 Hz,

C10], 135.1–135.4 [m (overlapped), C8, C4 and C6],

136.6 [dd, 2J(CP) = 11.1, 4J(CP) = 1.1 Hz, C2];31P{1H} (109.4 MHz): d = 27.9 [unresolved m, P(9)],

90.6 [P(1); 4J(PP) �1.7 Hz], for the interpretation of

the spectra see text; assignment of 13C and 1H NMR

spectra was made with help of 31P, 1H{31P}, H–HDQF COSY, H–C HSQC, H–C HSQC TOCSY and

H–P HMQC experiments. MS (EI+): m/z 330 (M+),

315 (M–Me), 283 (M–OMe–O), 251 (C10H6PS(OMe)2base peak), 189(C10H6P2H).

2.2. Preparation and characterisation of 4

Compound 2 (0.41 g) was subjected to flash chroma-

tography on silica gel using ethylacetate as eluent. The

product from column was further purified by recrystalli-

zation from hexane/toluene yielding pure 4 as pale yellow

crystals, some of them were suitable for X-ray work.Yield: 0.137 g (35%). M.p. 95–96 �C. C13H16O4P2Se:

Calc. C, 41.4; H, 4.3. Found: C, 41.7; H, 4.1%. IR

(KBr tablet, cm�1): m = 2974w, 2949m, 2837w (mC–H),1498m, 1226s (mP@O), 1202s, 1020 and 997vs (m(P)–O–C),

809s, 789s, 770s (mP–O–(C)), 607s; Ra (sealed capillary,

cm�1): m = 3075m, 3030w (mAr–H), 2951m, 2840w (mC–H),2447w (mP–H), 1559vs, 1334vs, 891s, 547vs, 352m.

NMR (CDCl3):1H (300 MHz): d = 3.46 [d, 3H,

3J(HP) = 12.3 Hz, H12], 3.63 and 3.80 [2 · d, 2 · 3H,3J(HP) = 14.1 Hz, H11], 7.49–7.60 [m (complex), 2H,

H3 and H7], 7.93–8.01 [m (complex), 2H, H4 and H6],

8.27 [ddd, 1H, 3J(HH) = 7.3, 4J(HH) = 1.4,3J(HP) = 19.8 Hz, H2], 8.43 [ddd, 1H, 3J(HH) = 7.3,4J(HH) = 1.4, 3J(HP) = 15.0 Hz, H8], 8.76 [d, 1H,1J(HP) = 613 Hz, H9]; 13C{1H} (75.5 MHz): d = 51.2

[d, 2J(CP) = 5.8 Hz, C12], 53.0 [d, 2J(CP) = 6.3 Hz,C11], 53.6 [d, 2J(CP) = 7.7 Hz, C11], 123.9 [d,3J(CP) = 16.9 Hz, C3], 124.3 [d, 3J(CP) = 12.4, C7],

128.2 [dd, 1J(CP) = 125.2, 3J(CP) = 2.2 Hz, C9], 128.7

[dd, 3J(CP) = 11.6 and 9.4 Hz, C5], 129.2 [dd,1J(CP) = 131.0, 3J(CP) = 2.5 Hz, C1], 133.1 [dd,2J(CP) = 11.9 and 10.8 Hz, C10], 133.6–133.7 [m (over-

lapped), C8 and C4 or C6], 133.9 [dd, 4J(CP) = 3.6 and

1.9 Hz, C4 or C6], 135.1 [dd, 2J(CP) = 13.0, 4J(CP) = 1.1

Hz, C2]; 31P{1H} (121.5 MHz): d = 29.1 (d, P9) and 97.1

[d with 77Se satellites, 1J(P,Se) = 875 Hz, P1],4J(PP) = 2.2 Hz, measurement of non-decoupled 31P

NMR confirmed magnitude of 1J(PH) = 613 Hz;77Se{1H} (51.5 MHz): d = �222 [dd, 1J(SeP) = 875,5J(SeP) = 15.4 Hz]; Assignment of 13C and 1H NMR

spectra was made with help of 31P, 1H{31P}, H–H

COSY, H–C HSQC, H–C HMBC and H–P HMBC

experiments. MS (EI+, probe heated to 180 �C): m/z

346 (M–MeOH), 331 (M–MeOH–Me), 299 (M–

Se + H, base peak), 284 (M–Se–Me + H), 237 (Nap-

P2O3H), 189 (NapP2H).

NMR numbering scheme for 3 and 4

PMeO

E

PHOMe

O

3 E = S4 E = Se

MeO 1

2

3

45

6

7

8

910

11 12

1

99

.

2.3. Structure determinations

All data were collected at 125K on a BrukerSMART CCD diffractometer equipped with Oxford

Instruments low temperature attachment, using Mo

Ka radiation (k = 0.71073 A). All refinements were

performed using SHELXTLSHELXTL (Version 5.10, Bruker

AXS, 1997). Full details of the structure determina-

tions of compounds 3 and 4 have been deposited with

the Cambridge Crystallographic Data Centre as

CCDC Nos. 234409 and 234410.

Appendix A. Supplementary material

Supplementary data associated with this article can

be found, in the online version, at doi:10.1016/

j.ica.2004.09.019.

References

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(2004) 1805.

P. Kilian et al. / Inorganica Chimica Acta 358 (2005) 1719–1723 1723

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