Cp*--Ruthenium-Nickel-Based H2-Evolving Electrocatalysts as Bio-inspired Models of NiFe Hydrogenases

Three dinuclear nickel-ruthenium complexes [Ni(xbsms)RuCp*(L)](PF6) [H(2)xbsms = 1,2-bis(4-mercapto-3,3-dimethyl-2-thiabutyl) benzene; Cp* = pentamethylcyclopentadienyl; L = CH3CN, CO and O-2] are reported that act as bio-inspired mimics of NiFe hydrogenases. Because of an increased electron density at the metal centres in comparison with the previously described [Ni(xbsms)RuCp(L)](PF6) (Cp = cyclopentadienyl) analogues, these compounds catalyze the evolution of hydrogen from Et3NH+ in DMF with an overpotential reduced by around 50 mV, thereby corroborating a previously established structure-function relationship [Eur. J. Inorg. Chem. 2007, 18, 2613-2626; Chem. Eur. J. 2009, 15, 9350-9364]. In addition, the steric protection provided by the bulky Cp*-ligand results in an increased catalytic rate and stability upon cycling.