Hydrogen production using cobalt-based molecular catalysts containing a proton relay in the second coordination sphere

Abstract

The cobalt analogue of a highly active nickel electrocatalyst for hydrogen production has been synthesized and characterized as [Co(P^Ph₂N^Ph₂)₂(CH₃CN)](BF₄)₂. In the presence of triflic acid in acetonitrile solution, the complex loses one cyclic diphosphine ligand to form [Co(P^Ph₂N^Ph₂)(CH₃CN)₃](BF₄)₂, which has been synthesized independently and stucturally characterized. The latter complex serves as an electrocatalyst for hydrogen formation with a turnover frequency of 90 s⁻¹ and an overpotential of 285 mV using bromoanilinium tetrafluoroborate as the acid. A similar cobalt complex with a related diphosphine ligand that does not contain a pendant base is not catalytically active, confirming an important role for the pendant amine in the catalytic reaction.