Hydrogen Evolution Mediated by Cobalt Diimine-Dioxime Complexes: Insights into the Role of the Ligand Acid/Base Functionalities.

The benchmarking of the performance for H₂ evolution of cobalt diimine-dioxime catalysts is provided based on a comprehensive study of their catalytic mechanism. The latter follows an ECE'CC pathway with intermediate formation of a Co(II)-hydride intermediate and second protonation possibly at a basic site of the ligand, acting as a proton relay. This suggests an intramolecular coupling between the hydride and protonated ligand as the proton concentration-independent rate-determining step controlling the turnover frequency for H₂ evolution.