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.