Electrochemical and Theoretical Investigations of the Oxidatively Induced Reactivity of the Complex [Fe2 (CO)4 (κ2 -dmpe)(µ-adtBn )] Related to the Active Site of [FeFe] Hydrogenases.

Electrochemical oxidation of the complex [Fe2 (CO)4 (κ2 -dmpe)(µ-adtBn )] (adtBn =(SCH2 )2 NCH2 C6 H5 , dmpe=Me2 PCH2 CH2 PMe2 ) (1) has been studied by cyclic voltammetry (CV) in acetonitrile and in dichloromethane in the presence of various substrates L (L=MeCN, trimethylphosphite, isocyanide). The oxidized species, [1-MeCN](PF6 )2 , [1-(P(OMe)3 )2 ](PF6 )2 and [1-(RNC)4 ](PF6 )2 (R=tert-butyl, xylyl), have been prepared and characterized by IR and NMR spectroscopies and, except [1-MeCN](PF6 )2 , by X-ray diffraction analysis. The crystallographic structures of the new FeII FeII complexes reveal that the association of one additional ligand (P(OMe)3 or RNC) occurs and, according to the nature of the substrates, further substitutions of one or three carbonyl groups, by P(OMe)3 or RNC, respectively, arise. Density functional theory (DFT) calculations have been performed to elucidate and discriminate, in each case, the mechanisms leading to the corresponding oxidized species. Moreover, the different degree of ligand substitution in the diiron core has been theoretically rationalized.

Influence of the Dithiolate Bridge on the Oxidative Processes of Diiron Models Related to the Active Site of [FeFe] Hydrogenases.

Electrochemical studies of [Fe2 (CO)4 (κ2 -dmpe)(µ-dithiolate)] (dithiolate=adtBn , pdt) and density functional theory (DFT) calculations reveal the striking influence of an amine functionality in the dithiolate bridge on their oxidative properties. [Fe2 (CO)4 (κ2 -dmpe)(µ-adtBn )] (1) undergoes two one-electron oxidation steps, with the first being partially reversible and the second irreversible. When the adtBn bridge is replaced with pdt, a shift of 60 mV towards more positive potentials is observed for the first oxidation whereas 290 mV separate the oxidation potentials of the two cations. Under CO, oxidation of azadithiolate compound 1 occurs according to an ECE process whereas an EC mechanism takes place for the propanedithiolate species 2. The dication species [1-CO]2+ resulting from the two-electron oxidation of 1 has been spectroscopically and structurally characterized. The molecular details underlying the reactivity of oxidized species have been explored by DFT calculations. The differences in the behaviors of 1 and 2 are mainly due to the presence, or not, of favored interactions between the dithiolate bridge and the diiron site depending on the redox states, FeI FeII or FeII FeII , of the complexes.