Electrochemical, EPR and Computational Results on [Fe2Cp2(CO)2]-Based Complexes with a Bridging Hydrocarbyl Ligand

The dimetallacyclopentenone complexes [Fe(2)Cp(2)(CO)(mu-CO){mu-eta(1):eta(3)-C(alpha)H=C(beta)(R)C(=O)}] (R = CH(2)OH, 1a; R = CMe(2)OH, 1b; R = Ph, 1c) were prepared by photolytic reaction of [Fe(2)Cp(2)(CO)(4)] with alkyne according to the literature procedure. The X-ray and the electrochemical characterization of 1c are presented. The mu-allenyl compound [Fe(2)Cp(2)(CO)(2)(mu-CO){mu-eta(1):eta(2)(alpha,beta) - C(alpha)H=C(beta)=CMe(2)][BF(4)] ([2][BF(4)]), obtained by reaction of 1b with HBF(4), underwent monoelectron reduction to give a radical species which was detected by EPR at room temperature. The EPR signal has been assigned to [Fe(2)Cp(2)(CO)(2)(mu CO) {mu-eta(1):eta(2)(alpha,beta)-C(alpha)H=C(beta)=CMe(2)}], [2](center dot). The molecular structures of [2](+) and [2](center dot) were optimized by DFT calculations. The unpaired electron in [2](center dot) is localized mainly at the metal centers and, coherently, [2](center dot) does not undergo carbon-carbon dimerization, by contrast with what previously observed for the mu-vinyl radical complex [Fe(2)Cp(2)(CO)(2)(mu-CO){mu-eta(1):eta(2)-CH=CH(Ph)}](center dot), [3](center dot). Electron spin density distributions similar to the one of [2](center dot) were found for the mu-allenyl radical complexes [Fe(2)Cp(2)(CO)(2)(mu-CO){mu-eta(1):eta(2)(alpha,beta)-C(alpha)H=C(beta)=C(R(1))(R(2))}](center dot) (R(1) = R(2) = H, [4](center dot); R(1) = H, R(2) = Ph, [5](center dot); R(1) = R(2) = Ph, [6](center dot)).