Azadithiolate-bridged [FeFe]-hydrogenase mimics with bridgehead N-derivation: structural and electrochemical investigations

To further develop the active site mimics of azadithiolate-bridged [FeFe]-hydrogenases, a series of new diiron azadithiolate complexes [{(μ-SCH₂)₂N(C₆H₄CH₂CH₂OC(O)R)}Fe₂(CO)₆] (R = CH₂C₆H₄Me-p, 2; C₆H₅, 3; CH₃, 4) bearing bridgehead N-derivation were successfully prepared by facile esterification reaction of parent complex [{(μ-SCH₂)₂N(C₆H₄CH₂CH₂OH)}Fe₂(CO)₆] (1) and different carboxyl compounds RCO₂H in the presence of 4-dimethylaminopyridine (DMAP) as catalyst and dicyclohexylcarbodiimide (DCC) as dehydrating reagent. Complexes 2–4 have been fully characterized by means of elemental analysis, FT-IR and NMR (¹H, ¹³C) spectroscopies, and especially for 2 by X-ray crystallography. Further electrochemical and electrocatalytic properties of target complexes 2–4 and reference analogue 1 were 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 (H₂).