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The synthesis and characterization of a half-sandwich cobalt(II) complex supported by a bidentate, pendent-amine phosphine ligand (PPh2NBn2 = 1,5-diaza-3,7-diphosphacyclooctane) are reported. Oxidation of a cobalt(I)-phosphine precursor with silver(I) salts yielded the paramagnetic complex [CpCo(PPh2NBn2)]+. This species rapidly reacts with oxygen upon air exposure under ambient conditions, resulting in the insertion of oxygen into the cobalt-phosphine bonds. The aerobic oxidation of the phosphine induces the exchange and rearrangement of the ligands at cobalt.
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Electrocatalytic Formate Oxidation by Cobalt-Phosphine Complexes
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.
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- Award ID(s):
- 2117792
- PAR ID:
- 10529782
- Publisher / Repository:
- ChemRxiv
- Date Published:
- Format(s):
- Medium: X
- Institution:
- Rutgers University
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Posted Content:
- https://doi.org/10.26434/chemrxiv-2023-tfn6t
