Deactivation of a Cobalt Catalyst for Water Reduction through Valence Tautomerism

5 years ago

Deactivation of a Cobalt Catalyst for Water Reduction through Valence Tautomerism

Cláudio N. Verani, Habib Baydoun, Shivnath Mazumder, H. Bernhard Schlegel

The activity of the water reduction catalyst [CoIII(L1)(pyr)2]PF6 (1), where (L1)2− is a bis-amido pyridine ligand and pyr is pyrrolidine, is investigated. Catalyst 1 has an overpotential of 0.54 V and a high observed TOF of 23 min−1, albeit for a relatively short time. Considering the significant activity of 1 and aiming to improve catalyst design, a detailed structural and electronic study is performed to understand the mechanisms of deactivation. Experimental and theoretical evidence support that the metal-reduced [CoI(L1)]− is in tautomeric equilibrium with the ligand-reduced [CoII(L1.)]− species. While [CoI(L1)]− favors formation of a CoIII−H− relevant for catalysis, the [CoII(L1.)]− species leads to ligand protonation, structural distortions, and, ultimatley, catalyst deactivation. Deactivate: A new Co-based water reduction catalyst displays a high TOF of 23 min−1, albeit for a relatively short time. A detailed structural and electronic study was performed to understand the mechanisms of deactivation and conclude that tautomeric equilibrium between [CoI(L1)]− and [CoII(L1.)]− takes place. While the [CoI(L1)]− state supports catalysis through CoIII-H− formation, the [CoII(L1.)]− state leads to catalyst deactivation. This knowledge is instrumental for the future design of robust catalysts.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201701783