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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 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 non-coordination sphere. Through individual examples, these processes involved in the electrochemistry of the iron carbonyl complexes are discussed. In probing the complexes involving 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 briefly summarised. Finally, the 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.

Infrared, Raman, and nuclear resonant vibrational (NRVS) spectroscopies have been used to address the Fe-H bonding in trans-Fe(H)(CO) iron hydride compound, Fe(H)(CO)(dppe)2, dppe = 1,2-bis(diphenylphosphino)ethane. H and D isotopomers of the compound, with the selective substitution at the metal-coordinated hydrogen, have been considered in order to address the Fe-H/D stretching and bending modes. Experimental results are compared to the normal mode analysis by the density functional theory (DFT). The results are that (i) the IR spectrum does not clearly show Fe–H stretching or bending modes; (ii) Fe–H stretching modes are clear but weak in the Raman spectrum, and Fe–H bending modes are weak; (iii) NRVS 57Fe spectroscopy resolves Fe-H bending clearly, but Fe–H or Fe–D stretching is above its experimentally resolved frequency range. DFT caclulations (with no scaling of frequencies) show intensities and peak locations that allow unambigous correlations between observed and calculated features, with frequency errors generally less than 15 cm−1. Prospects for using these techniques to unravel vibrational modes of protein active sites are discussed.

The reaction mechanism for the fragmentation of 7-azanorbornadiene derivatives (ANB; 7-azabicyclo[2.2.1]hepta-2,5-diene) mediated by iron carbonyl compounds was analyzed by substituent effects. The reactions proceed through two stages: a tetracarbonyliron complex (ANB)Fe(CO)4 forms first followed by a tricarbonyliron complex (ANB)Fe(CO)3. A linear free energy correlation was found for the decomposition of the latter group of complexes, which implied the existence of a polar transition state. The proposed mechanism was then confirmed by the isolation of new products from certain 2-tosyl ANB complexes in a related reaction.

Triiron dodecacarbonyl allows for the selective reduction of esters into the corresponding ethers. This protocol has a wide substrate scope. In addition, cholesteryl pelarogonate has been reduced under the reaction conditions with an excellent yield.

By using "click" chemistry between a diazide and a diiron model complex armed with two alkynyl groups, two polymeric diiron complexes (Poly-Py and Poly-Ph) were prepared. The two polymeric complexes were investigated using infrared spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), Mössbauer spectroscopy, and cyclic voltammetry (Poly-Py only, due to the insolubility of Poly-Ph). To probe the coordinating mode of the diiron units in the two polymeric complexes, two control complexes (3 and 4) were also synthesised using a monoazide. Complexes 3 and 4 were well characterised and the latter was further crystallographically analysed. It turns out that in both complexes (3 and 4) and the two polymeric diiron complexes, one of the two iron atoms in the diiron unit coordinates with one of the triazole N atoms. Our results revealed that both morphologies and properties of Poly-Py and Poly-Ph are significantly affected by the organic moiety of the diazide. Compared to the protonating behaviour of the complexes 3 and 4, Poly-Py exhibited proton resistance. In electrochemical reduction, potentials for the reduction of the diiron units in Poly-Py and hence its catalytic reduction of proton in acetic acid-DMF shifted by over 400 mV compared to those for complexes 3 and 4. It is likely that the polymeric nature of Poly-Py offers the diiron units a "protective" environment in an acidic medium and more positive reduction potential.

A number of stable derivatives of bis(chloromercury)–tetracarbonyliron with primary, secondary, and heterocyclic amines have been prepared. Replacement of one or two carbonyl groups may occur, depending upon the amine employed, to give six-co-ordinate complexes of iron. The compounds are non-electrolytes in nitrobenzene, and their infrared spectra are reported.

Intercalates of graphite with Fe(CO)5, with Na2–Fe(CO)4, and with Fe3(CO)12 have been prepared and characterized by X-ray diffraction, thermogravimetric analysis, Mossbauer spectroscopy, and electron microscopy.