Structure of diiodine adducts of some di- and tri-tertiaryphosphines in the solid state and in solution

Abstract

A series of ditertiaryphosphine–tetraiodine adducts R₂P(I₂)(CH₂)_nP(I₂)R₂ (R = Ph, n = 1–4; R = PhCH₂ or o-CH₃C₆H₄, n = 2) and two tritertiaryphosphine–hexaiodine adducts, PhP(CH₂CH₂PPh₂)₂I₆ and CH₃C(CH₂PPh₂)₃I₆ have been prepared and characterised by ³¹P-{H} solution NMR and Raman spectroscopy. In the case of Ph₂P(I₂)(CH₂)_nP(I₂)Ph₂ (n = 2 or 4), ³¹P-{H} NMR magic angle spinning NMR spectroscopy has been used to investigate the nature of the compounds in the solid state. In agreement with our previous extensive studies on the monophosphine derivatives, R₃PI₂, the tetraiododiphosphine compounds Ph₂P(I₂)(CH₂)_nP(I₂)Ph₂ (n = 2 or 4) isolated from diethyl ether contain molecular four-co-ordinate phosphorus centres onto which the diiodine is bound as a linear spoke, as indicated by their ³¹P-{H} NMR shifts obtained in CDCl₃ solution. Again, in agreement with our previous solution studies of the monophosphine derivatives R₃PI₂, the diphosphine–tetraiodine adducts completely ionise in CDCl₃ solution to produce the ionic compounds [R₂P(I)(CH₂)_nP(I)R₂]2I; the solution ³¹P-{H} NMR shifts are very similar to analogous solution shifts previously assigned to [R₃PI]I. The Raman band assignable to ν(P–I) has been identified for the compounds and a further band at lower frequency has been observed and assigned to ν(I–I). Although the solid-state NMR spectra of the triphosphine–hexaiodine adducts were not recorded, a band assignable to ν(I–I) was observed in the Raman spectrum, suggesting the molecular four-co-ordinate spoke structure also prevails for these hexaiodotritertiaryphosphine compounds in the solid state. From solution ³¹P-{H} NMR shifts these adducts also appear to ionise in CDCl₃ solution.

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