Electrocatalytic proton reduction by [Fe(CO)2(κ2-dppv)(κ1-SAr)2] (dppv = cis-1,2-bis(diphenylphosphino)ethylene; Ar = C6F5, C6H5, C6H4CH3-p)

Abstract

Electrocatalytic reduction of protons to hydrogen by mononuclear iron complexes which are developed as models of the distal iron center of [FeFe]-hydrogenase active site are described. A series of iron(II) bis(thiolate) complexes [Fe(CO)2(κ2-dppv)(κ1-SAr)2] (1, Ar=C6F5; 2, Ar=C6H4; 3, Ar=C6H4CH3-p; dppv=cis-1,2-bis(diphenylphosphino)ethylene) have been prepared from direct reactions between the corresponding hexacarbonyl [Fe2(CO)6(μ-SAr)2] and dppv at elevated temperatures. Structurally they are similar being coordinated by a chelating dppv, two carbonyls and two thiolate ligands bonded in an all cis-arrangement. Solution spectroscopic data indicate that they exist in two isomeric forms in solution. All reversibly protonate at sulphur atom(s) upon addition of HBF4·Et2O and lose a thiolate ligand as thiol. They show a common quasi-reversible reductive feature (attributed to the FeII/FeI couple) in their CVs in addition to other redox responses and are able to catalyze reduction of protons to hydrogen at their Fe(I) oxidation state in presence of HBF4·Et2O. Complex 1 is the most efficient catalyst and catalyzes proton reduction at ca. −1.5V showing icat/ip ≥46 in the presence of ten equivalents of HBF4·Et2O.