ACTIVATION OF CARBON-DIOXIDE BY ELECTRON-TRANSFER AND TRANSITION-METALS - MECHANISM OF NICKEL-CATALYZED ELECTROCARBOXYLATION OF AROMATIC HALIDES

In the presence of stoichiometric amounts of carbon dioxide, and catalytic amounts of Ni(II)(dppe)Cl2, electrolysis of bromobenzene results in the nearly quantitative formation of benzoic acid with negligible production of benzene or biphenyl. The mechanism of the nickel-catalyzed electrocarboxylation is shown to proceed through a chain reaction involving Ni(0), Ni(I), Ni(II), and Ni(III) intermediates, very reminiscent of that previously established for the nickel-catalyzed coupling of bromobenzene. Based on a detailed kinetic analysis of the propagation of this catalytic chain and of its competition with the biphenyl chain, all the key steps of the catalytic chain are identified and their rate constants determined.