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

A series of ditertiaryphosphine-tetraiodine adducts R2P(I-2) (CH2)(n)P(I-2)R-2 (R = Ph, n = 1-4; R = PhCH2 or o-CH3C6H4, n = 2) and two tritertiaryphosphine-hexaiodine adducts, PhP(CH2CH2PPh2)(2)I-6 and CH3C(CH2PPh2)(3)I-6 have been prepared and characterised by P-31-{H} solution NMR and Raman spectroscopy. In the case of Ph2P(I-2)(CH2)(n)P(I-2)Ph-2 (n = 2 or 4), P-31-{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(I-2)(CH2)(n)P(I-2)Ph-2 (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 P-31{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)(n)P(I)R-2]2I; the solution P-31-{H} NMR Shifts are very similar to analogous solution shifts previously assigned to [R3PI]I. The Raman band assignable to nu(P-I) has been identified for the compounds and a further band at lower frequency has been observed and assigned to nu(I-I). Although the solid-state NMR spectra of the triphosphine-hexaiodine adducts were not recorded, a band assignable to nu(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 P-31-{H} NMR shifts these adducts also appear to ionise in CDCl3 solution.