A synthesis of bisindolylmethanes catalyzed by an earth-abundant Mn(I)-NNSe pincer complex is presented, involving the reaction of indole with benzyl alcohol under solvent, additives, base, or hydrogen acceptor-free conditions.

Abstract

Here, we present a catalytic, regioselective synthesis of bisindolylmethanes through the reaction of indoles and benzyl alcohol derivatives mediated by metal-ligand cooperative catalysis. The reaction is catalyzed by an earth-abundant manganese-NNSe pincer complex without the need for base, solvent, additives, or hydrogen acceptors yielding water and dihydrogen as environmentally friendly by-products. Notably, C-3 and N-alkylation of indole, commonly observed in similar reactions were not detected. Mechanistic studies suggest that metal-ligand cooperative catalysis by the Mn(I)-NNSe pincer complex initiates the conversion of benzyl alcohol to benzaldehyde through dihydrogen elimination, which subsequently facilitates the synthesis of bisindolylmethane derivatives. To highlight the practical utility of this method, a wide range of substrates can be activated with low catalyst loading under mild reaction conditions.