Nickel-ruthenium-based complexes as biomimetic models of [NiFe] and [NiFeSe] hydrogenases for dihydrogen evolution

Abstract

The two heterodinuclear nickel-ruthenium complexes [Ni(xbSmS)RuCp(PPh3)]PF6 and [Ni(xbSmSe)RuCp(PPh3)]PF6 (H2xbSmS = 1,2-bis(4-mercapto-3,3-dimethyl-2-thiabutyl)benzene, H2xbSmSe = 1,2,-bis(2-thiabutyl-3,3-dimethyl-4-selenol)benzene, Cp = cyclopentadienyl) were synthesized as biomimetic models of [NiFe] and [NiFeSe] hydrogenases. The X-ray structural analyses of the complexes show that the two NiRu complexes are isomorphous; in both NiRu complexes the nickel(ii) centers are coordinated in a square-planar environment with two thioether donor atoms and two thiolate or selenolate donors that are bridging to the ruthenium(ii) center. The Ru(ii) ion is further coordinated to a η5-cyclopentadienyl group and a triphenylphosphane ligand. These complexes catalyze hydrogen evolution in the presence of acetic acid in acetonitrile solution at around -2.20 V vs. Fc+/Fc with overpotentials of 810 and 830 mV, thus they can be regarded as functional models of the [NiFe] and [NiFeSe] hydrogenases.