Complexes of Bi- and ter-valent nickel with olefinic ditertiary arsines

Abstract

The reaction of nickel(II) salts with 1,2-bis(dimethylarsino)ethylene (edas)(ca. 90%trans, 10%cis) gives complexes of both isomers. Complexes of cis-edas are obtained in high yield by irradiation of the reactants with u.v. light. The nickel(II) halide complexes of trans-edas are octahedrally co-ordinated polymers with two unpaired electrons, in which the ligand probably bridges pairs of metal atoms. The cis-ligand acts as a bidentate chelate group in forming diamagnetic NiX₂(cis-edas)₂(X = Cl, Br, I, NCS, or NO₃) and [NiX(cis-edas)₂]PF₆(X = Cl, Br, or NCS), which are probably five-co-ordinate in solution and tetragonally distorted octahedral in the solid state. The planar [Ni(cis-edas)₂]²⁺ and five-co-ordinate [Ni(cis-edas)₃]²⁺ species are also described. A paramagnetic complex NiCl₂(cis-edas) readily undergoes aerial oxidation to nickel(III), and complexes of general formula [NiX₂(cis-edas)₂]Y (X = Cl, Br, or PF₆) having one unpaired electron are described. Evidence for an unstable nickel(IV) complex of cis-edas is obtained. Isomerically pure cis- and trans-edas are displaced from their nickel(II) complexes and are identified by their ¹H n.m.r. and i.r. spectra, and by their different reactions with methyl iodide. Electronic and i.r. spectra are given for the complexes, and the complexing behaviour of cis-edas is compared with that of other bidentate ditertiary phosphines and arsines. A general similarity to o-phenylenebis(dimethylarsine) is evident, though this ligand appears to stabilise higher oxidation states better than does cis-edas.