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

Cyclic voltammetry, controlled-potential electrolysis, and spectroelectrochemistry have been employed to investigate and characterize the catalytic reduction of ethyl chloroacetate by cobalt(I) salen, electrogenerated at a carbon cathode in dimethylformamide containing tetraalkylammonium salts as supporting electrolytes. A cyclic voltammogram for the reduction of cobalt(II) salen in the presence of excess ethyl chloroacetate exhibits a prewave, which is attributed to the formation of an ethoxycarbonylmethylcobalt(III) salen complex. This prewave is followed by a large catalytic wave which involves the formation of both ethoxycarbonylmethyl and ethoxide anions; the first anion then undergoes a series of chemical reactions with the remaining starting material (ethyl chloroacetate) to yield ethyl acetate and 1,2,3-cyclopropane tricarboxylic acid triethyl ester, whereas ethoxide is protonated to afford ethanol. From the results obtained by means of cyclic voltammetry and controlled-potential electrolysis, a mechanism is proposed to explain our findings, and the validity of this mechanism has been probed with the aid of experiments involving the liquid chromatographic separation and mass spectrometric identification of the ethoxycarbonylmethylcobalt(III) salen complex.