Mechanism of the electrochemical reduction of [Fe(eta(5)-C6H7)(CO)(3)][PF6] - a theoretical approach to the intermediates

A mechanism is proposed for the electrochemical reduction of [Fe(eta (5)-C6 H7)(CO)(3)][PF6] based on cyclic voltammetry and simulation techniques. In [NBu4][X]/CH3CN (X = BF4 or ClO4) but not in [NBu4][BF4]/CH2Cl2, a rapid eq uilibrium prior to the electron transfer process is identified between [Fe( eta (5)-C6H7)(CO)(3)][PF6] and a species formulated as [Fe(eta (3)-C6H7)(CO )(3)(NCMe)](+). The formation of the species under equilibrium involves sol vent coordination and eta (5) to eta (3) ring slippage of the cyclohexadien yl ligand as the response of the system to the high electron count. Electro chemical electron transfer to [Fe(eta (3)-C6H7)(CO)(3)(NCMe)](+) affords a highly reactive 19-clectron intermediate exhibiting chemical reactivity (EC E mechanism) that leads to the formation of dimer-type species. A 'father-s on' type mechanism is proposed for the formation of the products of the ele ctrochemical reduction of [Fe(eta (5)-C6H7)(Co)(3)][PF6]. All the species i nvolved in the mechanism were analysed by theoretical means and are propose d on the basis of calculations made with the B3LYP HF/DFT hybrid functional . (C) 2001 Elsevier Science B.V. All rights reserved.