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Electrochemical Reduction of [Ni(Mebpy) 3 ] 2+ : Elucidation of the Redox Mechanism by Cyclic Voltammetry and Steady‐State Voltammetry in Low Ionic Strength Solutions
Author(s) -
Barman Koushik,
Edwards Martin A.,
Hickey David P.,
Sandford Christopher,
Qiu Yinghua,
Gao Rui,
Minteer Shelley D.,
White Henry S.
Publication year - 2020
Publication title -
chemelectrochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.182
H-Index - 59
ISSN - 2196-0216
DOI - 10.1002/celc.202000171
Subject(s) - comproportionation , cyclic voltammetry , redox , chronoamperometry , chemistry , electron transfer , electrochemistry , voltammetry , ionic strength , inorganic chemistry , ionic bonding , analytical chemistry (journal) , aqueous solution , electrode , ion , organic chemistry
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 ).