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 CoI in catalysts used for proton/water reduction. The ligand incorporates water upon metal coordination and is water soluble. This CoIII species is doubly reduced to CoI 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.