Insights into the Two‐Electron Reductive Process of [FeFe]H2ase Biomimetics: Cyclic Voltammetry and DFT Investigation on Chelate Control of Redox Properties of [Fe2(CO)4(κ2‐Chelate)(μ‐Dithiolate)]

The electrochemical reduction of complexes [Fe2(CO)4(κ2‐phen)(μ‐xdt)] (phen=1,10‐phenanthroline; xdt=pdt (1), adtiPr (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, adtiPr bridge and even virtual species [Fe2(CO)4(κ2‐phen)(μ‐adtR)] (R=CH(CF3)2, H) or [Fe2(CO)4(κ2‐phen)(μ‐pdtR)] (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. [ABSTRACT FROM AUTHOR]