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

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 1 e 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 2 e 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 (∼10 s −1 ).