Insights Into The Two-Electron Reductive Process Of [Fefe]H(2)Ase Biomimetics: Cyclic Voltammetry And Dft Investigation On Chelate Control Of Redox Properties Of [Fe-2(Co)(4)(Kappa(2)-Chelate)(Mu-Dithiolate)]

The electrochemical reduction of complexes [Fe-2(CO)(4)(kappa(2)-phen)(mu-xdt)] (phen=1,10-phenanthroline; xdt=pdt (1), adt(iPr) (2)) in MeCN-[Bu4N][PF6] 0.2 m is described as a two-reduction process. DFT calculations show that 1 and its monoreduced form 1(-) display metal- and phenanthroline-centered frontier orbitals (LUMO and SOMO) indicating the non-innocence of the phenanthroline ligand. Two energetically close geometries were found for the doubly reduced species suggesting an intriguing influence of the phenanthroline ligand leading to the cleavage of a Fe-S bond as proposed generally for this type of complex or retaining the electron density and avoiding Fe-S cleavage. Extension of calculations to other complexes with edt, adt(iPr) bridge and even virtual species [Fe-2(CO)(4)(kappa(2)-phen)(mu-adt(R))] (R=CH(CF3)(2), H) or [Fe-2(CO)(4)(kappa(2)-phen)(mu-pdt(R))] (R=CH(CF3)(2), iPr) showed that the relative stability between both two-electron-reduced isomers depends on the nature of the bridge and the possibility to establish a remote anagostic interaction between the iron center {Fe(CO)(3)} and the group carried by the bridged-head atom of the dithiolate group.