Hydrogen Production Catalyzed by Bidirectional, Biomimetic Models of the [FeFe]-Hydrogenase Active Site.

Active site mimics of [FeFe]-hydrogenase are shown to be bidirectional catalysts, producing H upon treatment with protons and reducing equivalents. This reactivity complements the previously reported oxidation of H by these same catalysts in the presence of oxidants. The complex Fe(adt)(CO)(dppv)(PFc* ) ([]; adt = (SCH)NBn, dppv = -1,2-bis(diphenylphosphino)ethylene, PFc* = EtPCHCMeFeCp*) reacts with excess [H(OEt)]BAr (BAr = B(CH-3,5-(CF))) to give ∼0.5 equiv of H and [Fe(adtH)(CO)(dppv)(PFc* )] ([H]). The species [H] consists of a ferrocenium ligand, an N-protonated amine, and an FeFe core. In the presence of additional reducing equivalents in the form of decamethylferrocene (Fc*), hydrogen evolution is catalytic, albeit slow. The related catalyst Fe(adt)(CO)(dppv)(PMe) () behaves similarly in the presence of Fc*, except that in the absence of excess reducing agent it converts to the catalytically active μ-hydride derivative [μH]. Replacement of the adt in [] 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.