Ni(II)-N′NN′ pincer complexes catalyzed dehydrogenation of primary alcohols to carboxylic acids and H2 accompanied by alcohol etherification

Acceptorless dehydrogenation of alcohols to carboxylic acid derivatives catalyzed by a transition metal complex is an important reaction in modern organic synthesis and catalysis, for which nickel complexes have rarely been developed. Herein we report three Ni(II)) complexes bearing pyridine-based N'NN' type pincer ligands, which catalyze the acceptorless dehydrogenation of primary alcohols to carboxylic acids under anhyrous conditions. The complex [NiCl2(L3)] 3 ( L3 = 2,6-bis(diethylaminomethyl) pyridine) displays the best catalytic reactivity, catalyzing the primary alcohols to carboxylic acids and H-2 in good yields (40-90%). Further investigation reveals that an unexpected alcohol etherification occurs, which gives the second oxygen atom for the formation of the carboxylic acid. Our results give a thread for the design of new nickel complexes without phosphine and N- heterocycle carbene ligands for the acceptorless oxidation of alcohols.