PREPARATION AND ELECTROCHEMICAL REACTIONS OF NICKEL(II) COMPLEXES CONTAINING ISOCYANIDE AND MONO-PHOSPHINES OR DI-PHOSPHINES

Reactions of cis-NiCl2(diphos) (diphos = PPh2(CH2)(n)PPh2: n = 2 (dppe ); n = 3 (dppp)) with isocyanide in the presence of NH4PF6 gave [NiCl( diphos)(XylNC)(2)](PF6) (1, 2) or [Ni(diphos)(RNC)(3)](PF6)(2) (3, 4) (R = 2,6-Me3C6H3 (Xyl), 2,4,6-Me3C6H2 (Mes)). Similar reactions of NiC l,(PPh,), with xylyl isocyanide gave [NiCl(PPh3)(2)(XylNC)(2)](PF6) 5 and [Ni(PPh3)(2)(XylNC)(3)](PF6)(2) 6. The structures of these five-co ordinated complexes were confirmed to be square-pyramidal by X-ray ana lyses: [NiCl(dppp)(XylNC)(2)](PF6). CH2Cl2 2a, a = 13.345(2) Angstrom, b = 10.984(2) Angstrom, c = 33.082(4) Angstrom, beta = 97.13(1)degree s, V = 4812(3) Angstrom(3), monoclinic, P2(1)/c, z=4, R = 0.064; [Ni(d ppe>(MesNC)(3)](PF6)(2) 3b, a = 12.763(3) Angstrom, b = 13.110(3) Angs trom, c = 17.114(3) Angstrom, beta = 102.55(2)degrees, V = 2795(2) Ang strom(3), monoclinic, Pn, z = 2, R = 0.051; [NiCl(PPh3)(2)(XylNC)(2)]( PF6) 5a, a = 13.768(5) Angstrom, b = 17.23(1) Angstrom, c = 11.063(6) Angstrom, alpha = 98.86(4)degrees, beta=95.97(4)degrees, gamma = 75.48 (3)degrees, V = 2504(2) Angstrom(3), triclinic, P1, z = 2, R = 0.063. The CV's of these complexes showed to be quasi-reversible with two-ele ctron transfer. The potentials of complexes (1, 2, 5) shifted to more negative region than those of the corresponding 3, 4, and 6, respectiv ely. There exists an equilibrium between 1 and 3 in the presence of is ocyanide on the basis of the E-1/2 potentials, but no equilibrium betw een 2 and 4. Complex 5 was completely converted to 6 in the presence o f xylyl isocyanide. These complexes were not influenced for excess dip hosphine. (C) 1997 Elsevier Science S.A.