The reaction of triorganophosphorus diiodides, R 3PI 2, with zinc metal powder; dependency of product on R; the X-ray crystal structures of dimeric {ZnI 2[P(NMe 2) 3]} 2 and monomeric ZnI 2(PPh 2Me) 2

Abstract

Seventeen zinc(II) tertiary phosphine complexes have been synthesised directly from elemental zinc by reaction with the reagents R 3PI 2. The complexes have been characterised by elemental analysis and 31P{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 R 3PI 2 with zinc metal powder in diethyl ether in a 1:1 stoichiometric ratio, produces the dimeric complexes [ZnI 2(PR 3)] 2, analogous to the previously reported [ZnI 2(PEt 3)] 2. In contrast, reaction of R 3PI 2 (R=Ph 3, Ph 2Et, Ph 2Me) with zinc metal powder produces the monomeric bis complexes ZnI 2(PR 3) 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 {ZnI 2[P(NMe 2) 3]} 2 and monomeric ZnI 2(PPh 2Me) 2 are also described. The formation of the bis complexes ZnI 2(PR 3) 2 (R 3=Ph 3, Ph 2Me, Ph 2Et) 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 Π–Π interactions on the ligands and crystal packing forces.