Distinct Proton and Water Reduction Behavior with a Cobalt(III) Electrocatalyst Based on Pentadentate Oximes

A new pentadentate oxime has been designed to drive the preferential coordination favored by Co^I in catalysts used for proton/water reduction. The ligand incorporates water upon metal coordination and is water soluble. This Co^III species is doubly reduced to Co^I and exhibits H⁺ reduction activity in the presence of weak acids in MeCN and evolves H₂ upon protonation suggesting that the ligand design increases catalyst effectiveness. Superior catalysis is observed in water with a turnover number (TON) of 5700 over 18 h. However, the catalyst yields Co‐based nanoparticles, indicating that the solvent media may dictate the nature of the catalyst.