Multiple‐Site Concerted Proton–Electron Transfer in a Manganese‐Based Complete Functional Model for [FeFe]‐Hydrogenase

Abstract

AbstractThe active site of [FeFe]‐hydrogenase (H2ase) is preorganized with an amine (azadithiolate) as a proton relay and a [4Fe4S] subunit as an electron reservoir, which together lower the overpotential for proton reduction and hydrogen oxidation by multiple‐site concerted proton–electron transfer (MS‐CPET). Herein, we report a mononuclear manganese complex, fac‐[Mn(CO)3(6‐(2‐hydroxyphenol)‐2‐pyridine‐2‐quinoline) Br] (1), as a rare model to fully mimic the functions of the H2ase. In 1, a redox‐active bidentate ligand with a pendent phenol replicates the roles of the electron reservoir and the proton relay in the enzyme. Experimental and theoretical studies revealed two consecutive MS‐CPET processes in the catalytic cycle, in each of which an electron stored in the reductive ligand and a proton at the proximal phenol moiety are transferred to the Mn center in a concerted way. By virtue of this mechanism, complex 1 exhibited a low overpotential comparable to that of natural enzyme in electrochemical hydrogen production using phenol as a proton source.