Insights into the Two-Electron Reductive Process of [FeFe]H2 ase Biomimetics: Cyclic Voltammetry and DFT Investigation on Chelate Control of Redox Properties of [Fe2 (CO)4 (κ2 -Chelate)(μ-Dithiolate)]

Abstract

The electrochemical reduction of complexes [Fe₂ (CO)₄ (κ² -phen)(μ-xdt)] (phen=1,10-phenanthroline; xdt=pdt (1), adt^iPr (2)) in MeCN-[Bu₄ N][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 [Fe₂ (CO)₄ (κ² -phen)(μ-adt^R )] (R=CH(CF₃ )₂ , H) or [Fe₂ (CO)₄ (κ² -phen)(μ-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.

Keywords: cyclic voltammetry; density functional calculations; diiron dithiolate bioinspired compound; non-innocent ligands; potential inversion.