Electronic Effects on a Mononuclear Co Complex with a Pentadentate Ligand for Catalytic H2 Evolution

Previous studies of Co catalysts for H-2 evolution have shown opposite effects between the redox potentials of Co centers and their catalytic properties such as the overpotential and turnover frequency: Co catalysts with more positive reduction potentials from structural modification display insignificant changes in the overpotential for H-2 evolution and require stronger acid for catalysis, and Co catalysts with lower overpotentials show decreased turnover frequency for H-2 evolution. In order to explore the electronic effects of a ligand scaffold on the catalytic properties for H-2 evolution by a Co complex with a pentadentate ligand, N,N-bis(2-pyridinylmethyl)-2,2'-bipyridine-6-methanamine (DPA-Bpy), we replaced the pyridyls in DPA-Bpy with more basic isoquinoline groups. In contrast to data from previously reported studies, in the current study, a Co complex with a more positive reduction potential, resulting from the replacement of pyridyls with isoquinoline groups, leads to a lower overpotential and higher turnover frequency for both electro- and photocatalytic H-2 production in neutral aqueous solution.