Ligand Transformations and Efficient Proton/Water Reduction with Cobalt Catalysts Based on Pentadentate Pyridine-Rich Environments

摘要

A series of cobalt complexes with pentadentate pyridine-rich ligands is studied. An initial Co-II amine complex 1 is prone to aerial oxidation yielding a Co-III imine complex 2 that is further converted into an amide complex 4 in presence of adventitious water. Introduction of an N-methyl protecting group to the ligand inhibits this oxidation and gives rise to the Co-II species 5. Both the Co-III 4 and Co-II 5 show electrocatalytic H-2 generation in weakly acidic media as well as in water. Mechanisms of catalysis seem to involve the protonation of a Co-II-H species generated in situ.