Reversible isomerization of a novel [FeFe]‑hydrogenase model complex and water-promoted electrocatalytic proton reduction

•μ-(SCH(CH2CH3)CH2S)-Fe2(CO)4(κ2-DPPE) (complex 1), which can be regarded as the active site model of [FeFe]-hydrogenase, was synthesized and characterized.•The reversible transition of complex 1 under N2 and CO atmosphere was observed by CV and IR, and a possible isomerization mechanism was proposed.•A small amount of H2O (CH3CN: H2O = 50:1, v/v) can increase the efficiency of electrocatalytic proton reduction of complex 1.•CO atmosphere or addition of H2O in CH3CN can trigger the same inversion of configuration of complex 1.

μ-(SCH(CH2CH3)CH2S)-Fe2(CO)4(κ2-DPPE) (complex 1, DPPE is 1,2-bis (diphenylphosphor) ethane), which can be regarded as a model of the [FeFe]‑hydrogenase active site, was synthesized and characterized. The reversible isomerization of complex 1 under N2 and CO atmosphere was demonstrated by cyclic voltammetry, IR spectroscopy and 31P NMR. Furthermore, we discovered that both the presence of a CO atmosphere and the addition of H2O can independently trigger the same inversion of configuration of complex 1. The electrocatalytic proton reduction capacity of 1 was evaluated under varying conditions. It was found that addition of a little H2O to CH3CN can facilitate its efficiency of electrocatalytic proton reduction. The possible mechanism of transition between axial/basal and dibasal isomers and the function of H2O in the electrocatalytic reaction are discussed.

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