Electrochemical Reduction of [Ni(Mebpy)(3)](2+): Elucidation of the Redox Mechanism by Cyclic Voltammetry and Steady-State Voltammetry in Low Ionic Strength Solutions

摘要

Bipyridine complexes of Ni are used as catalysts in a variety of reductive transformations. Here, the electroreduction of [Ni(Mebpy)(3)](2+) (Mebpy=4,4 '-dimethyl-2,2 '-bipyridine) in dimethylformamide is reported, with the aim of determining the redox mechanism and oxidation states of products formed under well-controlled electrochemical conditions. Results from cyclic voltammetry, steady-state voltammetry (SSV) and chronoamperometry demonstrate that [Ni(Mebpy)(3)](2+) undergoes two sequential 1e reductions at closely separated potentials (E-1(0')=-1.06 +/- 0.01 V and E-2(0')=-1.15 +/- 0.01 V vs Ag/AgCl (3.4 M KCl)). Homogeneous comproportionation to generate [Ni(Mebpy)(3)](+) is demonstrated in SSV experiments in low ionic strength solutions. The comproportionation rate constant is determined to be >10(6) M-1 s(-1), consistent with rapid outer-sphere electron transfer. Consequentially, on voltammetric time scales, the 2e reduction of [Ni(Mebpy)(3)](2+) results in formation of [Ni(Mebpy)(3)](+) as the predominant species released into bulk solution. We also demonstrate that [Ni(Mebpy)(3)](0) slowly loses a Mebpy ligand (similar to 10 s(-1)).