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