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)2NCH2C6H5, dmpe=Me2PCH2CH2PMe2) (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 FeIIFeII 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.