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−CαHCβ(R)C(O)}] (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−CαHCβCMe2][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–CαHCβCMe2}], [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–CHCH(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–CαHCβC(R1)(R2)}]• (R1 = R2 = H, [4]•; R1 = H, R2 = Ph, [5]•; R1 = R2 = Ph, [6]•).

Graphical abstractThe μ-allenyl complex [Fe2Cp2(CO)2(μ–CO){μ−η1:η2α,β−CαHCβCMe2][BF4] undergoes monoelectron reduction which does not result in formation of [Fe]4 derivatives, in contrast with what observed for analogous diiron μ-vinyl species.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Electrochemical/X-ray characterization of diiron cyclopentenone complex is given. ► Cationic diiron μ-allenyl complexes undergo monoelectron reduction. ► Elongation of the Fe–Fe interaction occurs upon monoelectron reduction. ► The unpaired electron is mainly localized at the metal centers (DFT, EPR). ► The spin density maps account for the chemistry of the parent complexes.