Electrocatalytic Formate Oxidation by Cobalt-Phosphine Complexes

06 December 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


We report a family of cobalt complexes based on bidentate phosphine ligands with two, one, or zero pendent amine groups in the ligand backbone. The pendent amine complexes are active electrocatalysts for the formate oxidation reaction, generating CO2 with near-quantitative faradaic efficiency at moderate overpotentials (0.45 – 0.57 V in acetonitrile). These homogeneous electrocatalysts are the first cobalt example and second first-row transition metal example for formate oxidation. Thermodynamic measurements reveal these complexes are energetically primed for formate oxidation via hydride transfer to the cobalt center, followed by deprotonation of the resulting cobalt-hydride by formate acting as a base. The complex with the strongest cobalt- hydride bond, given by its thermodynamic hydricity, is the fastest electrocatalyst in this series, with an observed rate constant for formate oxidation of 135 ± 8 h−1 at 25 °C. Electrocatalytic turnover is not observed for the complex with no pendent amine groups: decomposition of the complex structure is evident in the presence of high formate concentrations.


Cobalt Complexes
Formate Oxidation
Molecular Electrocatalysis
Thermodynamic Hydricity

Supplementary materials

Supporting Information
Experimental procedures, crystallographic details, NMR spectra, cyclic voltammetry (CV) studies, electronic absorption spectra, thermochemical data, and formate oxidation data.


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