The reaction of triorganophosphorus diiodides, R3PI2, with zinc metal powder;: dependency of product on R;: the X-ray crystal structures of dimeric {ZnI2[P(NMe2)3]}2 and monomeric ZnI2(PPh2Me)2

Seventeen zinc(II) tertiary phosphine complexes have been synthesised directly from elemental zinc by reaction with the reagents R3PI2. The complexes have been characterised by elemental analysis and P-31{H} NMR spectroscopy. The present work represents the first comprehensive study of a wide variety of zinc(II) tertiary phosphine complexes containing different parent tertiary phosphines and the majority of the complexes are reported for the first time. In most cases, reaction of R3PI2 with zinc metal powder in diethyl ether in a 1:1 stoichiometric ratio, produces the dimeric complexes [ZnI2(PR3)](2), analogous to the previously reported [ZnI2(PEt3)](2). In contrast, reaction of R3PI2 (R = Ph-3, Ph2Et, Ph2Me) with zinc metal powder produces the monomeric bis complexes ZnI2(PR3)(2) and an equimolar quantity of zinc(II) iodide, the latter product being identified by X-ray powder diffraction. The X-ray crystal structures of dimeric {ZnI2[P(NMe2)(3)]}(2) and monomeric ZnI2(PPh2Me)(2) are also described. The formation of the bis complexes ZnI2(PR3)(2) (R-3 = Ph-3, Ph2Me, Ph2Et) is surprising and cannot be due to steric factors since complexes containing less bulky tertiary phosphines are shown to be dimeric and the adoption of a monomeric zinc(II) centre increases steric crowding at the metal atom. The existence of the bis complexes is therefore reasoned to be due to favourable Pi-Pi interactions on the ligands and crystal packing forces. (C) 1999 Elsevier Science S.A. All rights reserved.