The solution state of nickel(II) and nickel(I) in the presence of diphosphines in acetonitrile. A combined electroanalytical and spectrophotometric approach

The equilibria involving nickel(II), nickel(I) and nickel(0) in the presence of bidentate phosphine ligands in acetonitrile solution have been investigated by cyclic voltammetry, controlled-potential electrolysis, and spectrophotometry. The obtained results show that when both cone angles and PP distance make the diphosphine well-suited to act as a chelating ligand, only bis-chelate complexes of the type NiL2 are formed by nickel in all the three achieved oxidation states. Longer methylene chains interposed between the phosphorus atoms make the diphosphine less suited to act in a bidentate fashion, thus allowing lower-order complexes, e.g. NiLS2 (S = solvent), to be obtained for nickel in the +2 and +1 oxidation states. Evidence for the poor stability of the [NiILS2]+ complexes and for a higher-order complex of the type NiL3 for nickel(II) have also been obtained. The dependence of the reduction potentials on the nature of the diphosphine employed is discussed. © 1984