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 (κ 2 -dppv)(κ 1 -SAr) 2 ] ( 1 , Ar = C 6 F 5 ; 2 , Ar = C 6 H 4 ; 3 , Ar = C 6 H 4 CH 3 - p ; dppv =  cis -1,2-bis(diphenylphosphino)ethylene) have been prepared from direct reactions between the corresponding hexacarbonyl [Fe 2 (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 HBF 4 ·Et 2 O and lose a thiolate ligand as thiol. They show a common quasi-reversible reductive feature (attributed to the Fe II /Fe I 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 HBF 4 ·Et 2 O. Complex 1 is the most efficient catalyst and catalyzes proton reduction at ca. −1.5 V showing i cat / i p ≥46 in the presence of ten equivalents of HBF 4 ·Et 2 O.