A structural and spectroscopic study of tris-aryl substituted R3PI2 adducts

A series of Ar3PI2 adducts [Ar = (o-OCH3C6H4), (m-OCH3C6H4), (p-OCH3C6H4), (o-SCH3C6H4), (p-SCH3C6H4), (m-FC6H4), (p-FC6H4), (p-ClC6H4)] have been synthesized via the 1:1 reactions of Ar3P with di–iodine. The 31P{1H} NMR spectra of a series of Ar3PI2 adducts has been examined to resolve previous inconsistent reports. Ar3PI2 adducts do not ionize to [Ar3PI]I in CDCl3, and in many cases the molecular Ar3PI2 “spoke” adduct is stable in solution, with the degree of stability being highly dependent on the nature of the aryl group. The structures of the majority of these adducts have been established by X-ray diffraction studies. Whilst P–I and I–I bond lengths are primarily influenced by electronic effects, steric and crystal packing effects may also have an influence, as shown by the different polymorphs of (p-FC6H4)3PI2, where a change in the conformation of the aryl groups in one of the molecules results in a lengthening of the P–I bond and shortening of the I–I bond.

Graphical abstractThe conformation of the aryl groups in Ar3PI2 spoke adducts influences the different crystal packing motifs which result in formation of pairs of adducts. A change in conformation impacts on the steric properties, which in turn leads to differences in P–I and I–I bond lengths, although electronic effects are the primary factor influencing the magnitude of these bonds.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► X-ray diffraction studies of ECH3–(E = O, S) and halo-substituted Ar3PI2 adducts. ► Solution behaviour of Ar3PI2 adducts (ionic versus CT species). ► Influence of steric and crystal packing effects on P–I/I–I bonds in Ar3PI2 adducts. ► Conformational analysis of the aryl rings in Ar3PI2 adducts.