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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.

preprint
submitted on 31.01.2020 and posted on 03.02.2020 by Koushik Barman, Martin A. Edwards, David P. Hickey, Christopher Sandford, Yinghua Qiu, rui gao, Shelley D. Minteer, Henry White

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 (E0’1 = -1.06 ± 0.01 V and E02 = -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 > 106 M-1s-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]1+ as the predominant species released into bulk solution. We also demonstrate that [Ni(Mebpy)3]0 slowly loses a Mebpy ligand (~10 s-1).

Funding

CCI NSF Synthetic Organic Electrosynthesis Center (CHE-1740656)

EU for Horizon 2020 Marie Skłodowska-Curie Fellowship (grant no. 789399)

History

Email Address of Submitting Author

white@chem.utah.edu

Institution

University of Utah - Dept. of Chemistry

Country

United States

ORCID For Submitting Author

0000-0002-5053-0996

Declaration of Conflict of Interest

There are no conflicts of interest to declare.

Version Notes

About to be submitted version.

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