Direct and cobalt(I) salen-catalyzed reduction of 2,6-bis(chloromethyl)pyridine at carbon cathodes in acetonitrile

Cyclic voltammetry and controlled-potential electrolysis have been employed to investigate the direct and cobalt(I) salen-catalyzed reduction of 2,6-bis(chloromethyl)pyridine at carbon cathodes in acetonitrile containing tetramethylammonium tetrafluoroborate. A cyclic voltammogram for direct reduction of 2,6-bis(chloromethyl)pyridine indicates that the starting material undergoes stepwise cleavage of carbonchlorine bonds. Cyclic voltammograms for reduction of cobalt(II) salen in the presence of excess 2,6-bis(chloromethyl)pyridine exhibit three waves: (a) a prewave attributed to formation of cobalt(I) salen and its follow-up reaction with 2,6-bis(chloromethyl)pyridine to give, most likely, a 2,6-bis[(salen)cobalt(III)methyl]pyridine complex; (b) a large catalytic wave which involves reduction of the complex; and (c) another wave due to direct reduction of 2,6-bis(chloromethyl)pyridine. Controlled-potential electrolyses of 2,6-bis(chloromethyl)pyridine produce 2,6-lutidine, 3-(6-methylpyridin-2-yl)propionitrile, and bis(6-methyl-2-pyridylmethyl) ether. For the cobalt(II) salen–2,6-bis(chloromethyl)pyridine system, electrolyses at potentials corresponding to the second voltammetric peak give the same products in similar yields as for the direct reduction. Mechanisms for both the direct and catalytic reduction of 2,6-bis(chloromethyl)pyridine are proposed.