Electrochemical, EPR and computational results on [Fe2Cp2(CO)2]-based complexes with a bridging hydrocarbyl ligand

The dimetallacyclopentenone complexes [Fe2Cp2(CO)(μ−CO){μ−η1:η3−CαHdouble bond; length as m-dashCβ(R)C(double bond; length as m-dashO)}] (R = CH2OH, 1a; R = CMe2OH, 1b; R = Ph, 1c) were prepared by photolytic reaction of [Fe2Cp2(CO)4] with alkyne according to the literature procedure. The X-ray and the electrochemical characterization of 1c are presented. The μ-allenyl compound [Fe2Cp2(CO)2(μ−CO){μ−η1:η2α,β−CαHdouble bond; length as m-dashCβdouble bond; length as m-dashCMe2][BF4] ([2][BF4]), obtained by reaction of 1b with HBF4, underwent monoelectron reduction to give a radical species which was detected by EPR at room temperature. The EPR signal has been assigned to [Fe2Cp2(CO)2(μ−CO){μ−η1:η2α,β–CαHdouble bond; length as m-dashCβdouble bond; length as m-dashCMe2}], [2]•. The molecular structures of [2]+ and [2]• were optimized by DFT calculations. The unpaired electron in [2]• is localized mainly at the metal centers and, coherently, [2]• does not undergo carbon–carbon dimerization, by contrast with what previously observed for the μ-vinyl radical complex [Fe2Cp2(CO)2(μ−CO){μ−η1:η2–CHdouble bond; length as m-dashCH(Ph)}]•, [3]•. Electron spin density distributions similar to the one of [2]• were found for the μ-allenyl radical complexes [Fe2Cp2(CO)2(μ–CO){μ–η1:η2α,β–CαHdouble bond; length as m-dashCβdouble bond; length as m-dashC(R1)(R2)}]• (R1 = R2 = H, [4]•; R1 = H, R2 = Ph, [5]•; R1 = R2 = Ph, [6]•).