Recent developments in electrochemical investigations into iron carbonyl complexes relevant to the iron centres of hydrogenases.

In this brief review mainly based on our own work, we summarised the electrochemical investigations into those iron carbonyl complexes relevant to the iron centres of [FeFe]-and [Fe]-hydrogenases in the following aspects: (i) electron transfer (E) coupled with a chemical reaction (C), EC process, (ii) two-electron process with potential inversion (ECisoE), and (iii) proton-coupled electron transfer (PCET) and the role of an internal base group in the non-coordination sphere. Through individual examples, these processes involved in the electrochemistry of the iron carbonyl complexes are discussed. In probing the complexes involving a two-electron process with potential inversion, the co-existence of one- and two-electron for a complex is demonstrated by incorporating intramolecularly a ferrocenyl group(s) into the complex. Our studies on proton reduction catalysed by three diiron complexes involving the PCET mechanism are also summarised. Finally, perspectives of the electrochemical study in iron carbonyl complexes inspired by the iron-containing enzymes are mentioned in the sense of developing mimics of low overpotentials for hydrogen evolution through exploiting the PCET effect.