Catalytic reduction of iodoethane by cobalt(I) salen electrogenerated at vitreous carbon cathodes

Cyclic voltammetry and controlled-potential electrolysis have been employed to investigate and characterize the catalytic reduction of iodoethane by cobalt(I) salen electrogenerated at a carbon cathode in dimethylformamide or acetonitrile containing a tetraalkylammonium tetrafluoroborate as supporting electrolyte. A.cyclic voltammogram for reduction of cobalt(II) salen in the presence of excess iodoethane exhibits two peaks; the first is attributable to formation of cobalt(I) salen and its fast follow-up reaction with iodoethane to give ethylcobalt(III) salen, and the second is due to reduction of ethylcobalt(III) salen to yield cobalt(I) salen and an ethyl radical. Controlled-potential electrolyses of cobalt(II) salen-iodoethane systems at potentials corresponding to the second voltammetric peak produce n-butane, ethane, and ethylene; n-butane and ethylene arise, respectively, from coupling and disproportionation of ethyl radicals, whereas ethane is formed via disproportionation as well as hydrogen atom abstraction from the solvent. This mechanistic picture is supported by digital simulations of cyclic voltammograms and by separate studies of the electrochemical behavior and ultraviolet-visible spectrum of ethylcobalt(III) salen. (C) 1998 Elsevier Science S.A. All rights reserved.