Etude electrochimique de la labilite des complexes paramagnetiques η 5-cyclopentadienyle η 6-arene fer(I). Reaction d'echange de l'arene par le cyclopentadiene

Abstract

The decomposition of neutral electrogenerated η 5-cyclopentadienyl-η 6-arene iron(I) is investigated. The cyclic voltammetry shows that the cationic precursors η 5-CpFe II+-η 6-Ar are reduced in a one-electron transfer step followed by a chemical step which involves coordination of solvent molecules. The increasing stability of η 5-C 5H 5Fe I-η 6-C 6H 6 follows the order of solvent used: acetonitrile or pyridine < dimethylformamide < acetone or methylene chloride. In acetonitrile, the fast replacement of C 6H 6 by donor ligands occurs via a postulated intermediate, the 17-electron complex η 5-C 5H 5Fe I(CH 3CN) 2. Without donor ligands decomposition of η 5-CpFe I-η 6-Ar leads to the corresponding ferrocenes, Cp 2Fe II. In the presence of cyclopentadiene the electrochemical activation allows replacement of the arene group of η 5-CpFe II+-η 6-Ar by a cyclopentadienyl ligand.