H2 Binding and Splitting on a New-Generation [FeFe]-Hydrogenase Model Featuring a Redox-Active Decamethylferrocenyl Phosphine Ligand: A Theoretical Investigation

[FeFe]-hydrogenases are dihydrogen-evolving metalloenzymes that are able to combine substrate binding and redox functionalities, a feature that has important bearing on their efficiency. New-generation bioinspired systems such as Fe-2[(SCH2)(2)NBn](CO)(3)(Cp*Fe(C5Me4CH2PEt2))(dppv) were shown to mimic H-2 oxidation and splitting processes performed by the [FeFe]-hydrogenase/ferredoxin system, and key mechanistic aspects of such reaction are theoretically investigated in the present contribution. We found that H-2 binding and heterolytic cleavage take place concomitantly on DFT models of the synthetic catalyst, due to a substrate-dependent intramolecular redox process that promotes dihydrogen activation. Therefore, formation of an iron-dihydrogen complex as a reaction intermediate is excluded in the biomimetic system, at variance with the case of the enzyme. H-2 uptake at the synthetic system also requires an energetically disfavored isomerization of the amine group acting as a base during splitting. A possible strategy to stabilize the conformation competent for H-2 binding is proposed, along with an analysis of the reactivity of a triiron complex in which di(thiomethyl)amine-the chelating group naturally occurring in [FeFe]-hydrogenases-substitutes the benzyl-containing dithiolate ligand.