Cyclopentadienyl Ruthenium—Nickel Catalysts for Biomimetic HydrogenEvolution: Electrocatalytic Properties and Mechanistic DFT Studies

摘要

The new dinuclear nickel-ruthenium complexes [Ni-(xbsms)RuCp(L)][PF_6] (H_2xbsms = 1,2-bis(4-mercapto-3,3-dimethyl-2-thiabu- tyl)benzene; Cp- = cyclopentadienyl;L =DMSO, CO, PPh_3, and PCy_3) arereported and are bioinspired mimics ofNiFe hydrogenases. These compoundswere characterized by X-ray diffractiontechniques and display novel structuralmotifs. Interestingly, [Ni-(xbsms)RuCpCO][PF_6] is stereochemi-cally nonrigid in solution and an iso-merization mechanism was derived with the help of density functionaltheory (DFT) calculations. Because ofan increased electron density on themetal centers [Eur. J. Inorg. Chem.2007, 18, 2613-2626] with respect tothepreviouslydescribed[Ni-(xbsms)Ru(CO)_2Cl_2]and [Ni-(xbsms)Ru(p-cymene)Cl]~+ complexes,[Ni(xbsms)RuCp(dmso)][PF_6] catalyzes hydrogen evolution from Et_3NH~+ inDMF with an overpotential reduced by180 mV and thus represents the mostefficient NiFe hydrogenase functionalmimic. DFT calculations were carriedout with several methods to investigatethe catalytic cycle and, coupled withelectrochemical measurements, alloweda mechanism to be proposed. A termi-nal or bridging hydride derivative wasidentified as the active intermediate,with the structure of the bridging formsimilar to that of the Ni-C active stateof NiFe hydrogenases.