An electrochemical approach for the preparation of aryl compounds of cobalt(II)

Preparative-scale electrolyses, in a DMF+pyridine (v/v=9:1) mixture, in a cell fitted with a sacrificial cobalt anode, of arylbromides (ArBr) and CoBr2 allowed us to evidence the formation of arylcobalt(II) complexes which probably are of the type Ar2Co (Ar = C6H5, C6H5CO2Et, C6H5OCH3, C6F5). The formation of these species has also been shown by cyclic voltammetry. It is shown that the stability of these organometallic compounds is influenced by the nature of the substituents on the aromatic ring. The half-life times, under argon, of various arylcobalt(II) complexes have been estimated. The decomposition of these arylcobalt complexes leads to arene and biaryl in a ratio depending on the nature of ArBr. Interestingly, the arylcobalt(II) complex obtained from 4-bromoanisole reacts with allyl acetate to lead to the coupling product. (C) 2002 Elsevier Science B.V. All rights reserved.