Diiron Complexes Bearing Bridging Hydrocarbyl Ligands as Electrocatalysts for Proton Reduction

Diiron complexes with bridging hydrocarbyl ligands and containing CO and Cp ligands (Cp = η⁵-C₅H₅) have been investigated as possible electrocatalysts for H₂ production. In particular, studies included the vinyliminium complexes [Fe₂{μ-η¹:η³-C­(R′)=CRCNMe₂}­(μ-CO)­(CO)­(Cp)₂]­[SO₃CF₃] (R′ = Tol (4-MeC₆H₄), R = H, 1a; R′ = CH₂OH, R = H, 1b; R′ = CH₂OH, R = SPh, 1c), the vinylalkylidene [Fe₂{μ-η¹:η³-C­(Tol)­CHCHNMe₂}­(μ-CO)­(CO)­(Cp)₂] (2), the aminoalkylidyne [Fe₂{μ-CN­(Me)­(R)}­(μ-CO)­(CO)­(L)­(Cp)₂]­[SO₃CF₃] (R = Me, L = CO, 3a; R = Me, L = NCMe, 3b; R = Xyl (2,6-Me₂C₆H₃), L = CO, 3c), [Fe₂{μ-CN­(Me)₂}­(μ-L′)­(CO)­(L)­(Cp)₂] (L′ = CO, L = CN, 4; L′ = H, L = CO, 5), the thiocarbyne complexes [Fe₂(μ-CSEt)­(μ-CO)­(CO)₂(Cp)₂]­[BF₄], (6) and [Fe₂(μ-CSMe)­(μ-CO)­(CO)­(CN)­(Cp)₂] (7), and the alkylidene complexes [Fe₂{μ-C­(CN)­(SMe)}­(μ-CO)­(CO)₂(Cp)₂]­[SO₃CF₃] (8) and [Fe₂{μ-C­(CN)­(PMe₂Ph)}­(μ-CO)­(CO)₂(Cp)₂]­[SO₃CF₃] (9). Cyclic voltammograms (CV) of the above complexes in CH₃CN have been recorded in the presence of increasing amounts of acetic acid to evidence electrocatalytic proton reduction. In spite of the fact that the above diiron complexes do not resemble the typical diiron dithiolate model systems, the aminocarbyne 4 and the thiocarbyne complex 7 exhibit significant electrocatalytic properties for proton reduction (e.g., for 4, the turnover number (TON) is 15.5).