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 Fe2[(SCH2)2NBn](CO)3(Cp* Fe(C5Me4CH2PEt2))(dppv) were shown to mimic H2 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 H2 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. H2 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 H2 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. © 2013 American Chemical Society.