[FeFe]-Hydrogenase models featuring dithiolato-bridgehead functionality: Preparation, structures, and electrocatalytic proton reduction

To further develop the active site models of [FeFe]-hydrogenases, a new series of diiron model complexes [{(mu-SCH2)(2)CHCH2OC(O)C6H4I)}Fe-2(CO)(6)] (I is located at -para for 1, -meta for 2, and -ortho for 3) bearing dithiolato-bridgehead functionality were successfully prepared by treatments of bridghead-hydroxyl-containing parent complex [{(mu-SCH2)(2)CHCH2OH)}Fe-2(CO)(6)] (A) and three different iodobenzoic acids (IC6H4CO2H) in the presence of 4-dimethylaminopyridine (DMAP) as catalyst and dicyclohexylcarbodiimide (DCC) as dehydrating reagent. All these new complexes 1-3 have been fully characterized through elemental analysis, FT-IR and NMR (H-1, C-13) spectroscopies, and X-ray crystallography. Further electrochemical and electrocatalytic properties of complexes 1-3 are studied and compared in the absence and presence of acetic acid (HOAc) as a proton source by cyclic voltammetry (CV), indicating that they may be considered as the active biomimetic electrocatalysts for proton reduction to hydrogen (H-2).