Electroanalytical investigation on ligand-disproportionation and -exchange equilibria in nickel(II) and nickel(I) halide phosphine complexes in acetonitrile

Abstract

Redox reactions of [NiL₂X₂] complexes (L = PPh₃; X = Cl, Br, or I) at platinum electrodes in acetonitrile solution have been investigated by cyclic voltammetry, controlled-potential electrolysis, and spectrophotometry. The complexes undergo quantitative ligand disproportionation giving ionic species, and the nickel(I) complexes obtained as reduction products exhibit ligand-exchange equilibria. The nickel(0) species obtained in a further reduction process is not involved in any ligand-exchange reaction. The results demonstrate that the degree of reversibility of the redox processes depends markedly on the nature of the ligand set present in both the redox partners. The dependence of the reduction potentials on the nature of the halide ligands is discussed.