Preparation and electrochemical reactions of nickel(II) complexes containing isocyanide and mono- or di-phosphines

Article abstract of DOI:10.1016/S0022-328X(97)00343-4

Reactions of cis-NiCl₂(diphos) (diphos = PPh₂(CH₂)_nPPh₂: 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-Me₂C₆H₃ (Xyl), 2,4,6-Me₃C₆H₂ (Mes)). Similar reactions of NiCl₂(PPh₃)₂ 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-coordinated complexes were confirmed to be square-pyramidal by X-ray analyses: [NiCl(dppp)(XylNC)₂](PF₆) · CH₂Cl₂ 2a, a = 13.345(2) A, b = 10.984(2) A, c = 33.082(4) A, β = 97.13(1)°, V = 4812(3) A³, monoclinic, P2₁/c, z = 4, R = 0.064; [Ni(dppe)(MesNC)₃](PF₆)₂ 3b, α = 12.763(3) A, b = 13.110(3) A, c = 17.114(3) A, β = 102.55(2)°, V = 2795(2) A³, monoclinic, Pn, z = 2, R = 0.051; [NiCl(PPh₃)₂(XylNC)₂](PF₆) 5a, a = 13.768(5) A, b = 17.23(1) A, c = 11.063(6) A, α = 98.86(4)°, β = 95.97(4)°, γ = 75.48(3)°, V = 2504(2) A³, triclinic, P1, z = 2, R = 0.O63. The CV's of these complexes showed to be quasi-reversible with two-electron transfer. The potentials of complexes (1, 2, 5) shifted to more negative region than those of the corresponding 3, 4, and 6, respectively. There exists an equilibrium between 1 and 3 in the presence of isocyanide on the basis of the E_1/2 potentials, but no equilibrium between 2 and 4. Complex 5 was completely converted to 6 in the presence of xylyl isocyanide. These complexes were not influenced for excess diphosphine.