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

The cobalt analogue of a highly active nickel electrocatalyst for hydrogen production has been synthesized and characterized as Co(PPh2NPh2)2(CH3CN)(BF4)2. In the presence of triflic acid in acetonitrile solution, the complex loses one cyclic diphosphine ligand to form Co(PPh2NPh2)(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.