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 direc tly 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 variet y of zinc(II) tertiary phosphine complexes containing different parent tert iary phosphines and the majority of the complexes are reported for the firs t 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(P R3)](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 diffractio n. The X-ray crystal structures of dimeric {ZnI2[P(NMe2)(3)]}(2) and monome ric 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 ar e shown to be dimeric and the adoption of a monomeric zinc(II) centre incre ases 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 lig ands and crystal packing forces. (C) 1999 Elsevier Science S.A. All rights reserved.