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

Abstract

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(adtBn)(CO)3(dppv)(PFc*Et2) ([1]0; adtBn = (SCH2)2NBn, dppv = cis-1,2-bis(diphenylphosphino)ethylene, PFc*Et2 = Et2PCH2C5Me4FeCp*) reacts with excess [H(OEt2)2]BArF4 (BArF4– = B(C6H3-3,5-(CF3)2)4–) to give ∼0.5 equiv of H2 and [Fe2(adtBnH)(CO)3(dppv)(PFc*Et2)]2+ ([1H]2+). The species [1H]2+ consists of a ferrocenium ligand, an N-protonated amine, and an FeIFeI core. In the presence of additional reducing equivalents in the form of decamethylferrocene (Fc*), hydrogen evolution is catalytic, albeit slow. The related catalyst Fe2(adtBn)(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-H3]+. 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.

A Functional Hydrogenase Mimic Chemisorbed onto Fluorine‐Doped Tin Oxide Electrodes: A Strategy towards Water Splitting Devices

“…Hydrogenases, metalloenzymes that utilize iron, diiron or iron–nickel as metallic components, are able to perform reversible proton reduction at ambient temperature and pressure with activities, efficiencies, and overpotentials that are comparable to platinum . It is thus not surprising that chemists take inspiration from nature to mimic the active site of these metalloenzymes to develop new classes of proton reduction catalysts . Although several hundreds of hydrogenase model systems have been reported to date, most have been studied as homogeneous catalysts in organic solvents .…”

“…[6][7][8][9][10] It is thus not surprising that chemists take inspiration from naturet om imic the active site of these metalloenzymes to develop new classes of proton reduction catalysts. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] Although severalh undreds of hydrogenasem odel systems have been reportedt od ate, most have been studied as homogeneous catalysts in organic solvents. [28,29] Strategies to afford robust immobilization on conductive electrode surfaces, which are key for the development of devices,a re relatively limited.…”

Biomimetic Complexes for Production of Dihydrogen and Reduction of CO2

“…Rauchfuss and coworkers were the first to describe a bimetallic model of [FeFe]-hydrogenases capable of both catalytic hydrogen oxidation and proton reduction [58]. As shown in Fig.…”

Synthetic Models for Nickel–Iron Hydrogenase Featuring Redox-Active Ligands

“…[32] A later application of a ferrocenylphosphine as an electron source/sink allowed for the first example of H 2 oxidation catalyzed by a [FeFe]-H 2 ase model. [35,36] The conversion was mediated by a triiron complex [ c ] 2+ (Fig. 2) featuring both a H + relay (the amino group poised near the pyramidal Fe centre for substrate transfer) as well as a diethylphosphinomethyl(nonamethylferrocene) redox-active ligand.…”