Hydrogen Production Catalyzed by Bidirectional BiomimeticModels of the FeFe-Hydrogenase Active Site

摘要

Active site mimics of [FeFe]-hydrogenase are shown to be bidirectional catalysts, producing H2 upon treatment with protons and reducing equivalents. This reactivity complements the previously reported oxidation of H2 by these same catalysts in the presence of oxidants. The complex Fe2(adt^Bn)(CO)3(dppv)(PFc*^Et2) ([>1]⁰; adt^Bn = (SCH2)2NBn, dppv = cis-1,2-bis(diphenylphosphino)ethylene, PFc*^Et2 = Et2PCH2C5Me4FeCp*) reacts with excess [H(OEt2)2]BAr^F4 (BAr^F4^– = B(C₆H₃-3,5-(CF₃)₂)₄^–) to give ∼0.5 equiv of H₂ and [Fe₂(adt^BnH)(CO)₃(dppv)(PFc*^Et₂)]²⁺ ([>1H]²⁺). The species [>1H]²⁺ consists of a ferrocenium ligand, an N-protonated amine, and an Fe^IFe^I core. In the presence of additional reducing equivalents in the form of decamethylferrocene (Fc*), hydrogen evolution is catalytic, albeit slow. The related catalyst Fe₂(adt^Bn)(CO)₃(dppv)(PMe₃) (>3) behaves similarly in the presence of Fc*, except that in the absence of excess reducing agent it converts to the catalytically inactive μ-hydride derivative [μ>-H>3]⁺. Replacement of the adt in [>1]⁰ with propanedithiolate (pdt) results in a catalytically inactive complex. In the course of synthesizing [FeFe]-hydrogenase mimics, new routes to ferrocenylphosphine ligands and nonamethylferrocene were developed.