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

A series of cobalt complexes with pentadentate pyridine-rich ligands is studied. An initial CoII amine complex 1 is prone to aerial oxidation yielding a CoIII 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 CoII species 5. Both the CoIII 4 and CoII 5 show electrocatalytic H2 generation in weakly acidic media as well as in water. Mechanisms of catalysis seem to involve the protonation of a CoIIH species generated in situ.