Title

The Crystal Structures of (p-ClPh)3PO and (p-OMePh)3PO, Including an Analysis of the P-O Bond in Triarylphosphine Oxides

Document Type

Article

Publication Title

Journal of Chemical Crystallography

Department

Chemistry

ISSN

1074-1542

Volume

28

Issue

12

DOI

10.1023/A:1022850503138

First Page

893

Last Page

898

Publication Date

12-1-1998

Abstract

The crystal structures of the compounds tris(para-chlorophenyl)phosphine oxide {(p-ClPh)3PO} and tris(para-methoxyphenyl)phosphine oxide {(p-OMePh)3PO} were determined by X-ray diffraction methods. (p-ClPh)3PO crystallizes in the space group P-1 (no. 2) with a = 11.828(2), b = 12.645(2), c = 14.072(2) Å, α = 97.90(1), β = 109.45(1), γ = 115.43(1), V = 1692.3(2) Å3 and Z = 4. The mean O–P and C–P distances are 1.481(6) and 1.806(2) Å, respectively, and the mean C–P–C angle is 106.5(1.1). (p-OMePh)3PO crystallizes in the space group P21/c (no. 14) with a = 18.8642 (10), b = 10.3999(5), c = 21.3462(16) Å, β = 115.414(6)°, V= 3782.6(4) Å3, and Z = 8. The mean O–P and C–P distances are 1.484(5) and 1.798(4) Å, respectively, and the mean C–P–C angle is 106.5(1.0). These two structures were analyzed along with the previously determined structures of triphenylphosphine oxide {Ph3PO} and tri-p-tolylphosphine oxide {(p-MePh)3PO}, and IR data were collected on all four compounds. Both the observed P–O distances and the IR stretching frequencies for these triarylphosphine oxides support the interpretation of the P–O bond as having substantial multiple-bond character, with a bond order between 1.7 and 1.8. The para-substituents on these triarylphosphines were shown to have a statistically insignificant effect on the P–O bond.