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

• Published in: Journal of organometallic chemistry Vol. 696; no. 22; pp. 3551 - 3556
• Main Authors: Boni, Adriano, Funaioli, Tiziana, Marchetti, Fabio, Pampaloni, Guido, Pinzino, Calogero, Zacchini, Stefano
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2011
• Subjects: Allenyl ligand; DFT calculations; Diiron complexes; Dimetallacyclopentenone complexes; Electrochemistry; Vinyl ligand; Electrochemistry; Dimetallacyclopentenone complexes; Diiron complexes; Allenyl ligand; Vinyl ligand; DFT calculations
• ISSN: 0022-328X; 1872-8561
• DOI: 10.1016/j.jorganchem.2011.07.039

The dimetallacyclopentenone complexes [Fe 2Cp 2(CO)(μ−CO){μ−η 1:η 3−C αH C β(R)C( O)}] (R = CH 2OH, 1a; R = CMe 2OH, 1b; R = Ph, 1c) were prepared by photolytic reaction of [Fe 2Cp 2(CO) 4] with alkyne according to the literature procedure. The X-ray and the electrochemical characterization of 1c are presented. The μ-allenyl compound [Fe 2Cp 2(CO) 2(μ−CO){μ−η 1:η 2 α,β−C αH C β 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 2Cp 2(CO) 2(μ−CO){μ−η 1:η 2 α,β–C αH C β CMe 2}], [ 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 [Fe 2Cp 2(CO) 2(μ−CO){μ−η 1:η 2–CH CH(Ph)}] • , [ 3] • . Electron spin density distributions similar to the one of [ 2] • were found for the μ-allenyl radical complexes [Fe 2Cp 2(CO) 2(μ–CO){μ–η 1:η 2 α,β–C αH C β C(R 1)(R 2)}] • (R 1 = R 2 = H, [ 4] • ; R 1 = H, R 2 = Ph, [ 5] • ; R 1 = R 2 = Ph, [ 6] • ). The μ-allenyl complex [Fe 2Cp 2(CO) 2(μ–CO){μ−η 1:η 2 α,β−C αH C β CMe 2][BF 4] undergoes monoelectron reduction which does not result in formation of [Fe] 4 derivatives, in contrast with what observed for analogous diiron μ-vinyl species. [Display omitted] ► 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.