Electroreduction of organic compounds 32. Indirect electrodehalogenation of chloroarenes in methanol mediated by nickel complexes

The indirect electroreduction of chlorinated benzenes and dibenzofurans in methanol has been investigated. (2,2'-Bipyridyl)nickel(II) chloride (1) and (1,4,8,1 1-tetraazacyclotetradecane) nickel(II) chloride (2) were used as mediators for the electron transfer. The electrolyses were carried out pote ntiostatically at -1.4V vs. Ag/AgBr in a divided batch cell. Indirect reduc tion of more highly chlorinated benzenes lead to chlorobenzene as the main product. In case of the chlorodibenzofurans, reduction to unsubstituted dib enzofuran was achieved. Much higher selectivity in the mediated electroredu ction as compared with the direct cathodic reduction is observed. In partic ular the formation of hydrogenated products is completely suppressed.