Methanol Dehydrogenation by Iridium N-Heterocyclic Carbene Complexes

Abstract

A series of homogeneous iridium bis(N-heterocyclic carbene) catalysts are active for three transformations involving dehydrogenative methanol activation: acceptorless dehydrogenation, transfer hydrogenation, and amine monoalkylation. The acceptorless dehydrogenation reaction requires base, yielding formate and carbonate, as well as 2-3 equivalents of H2. Of the few homogeneous systems known for this reaction, our catalysts tolerate air and employ simple ligands. Transfer hydrogenation of ketones and imines from methanol is also possible. Finally, N-monomethylation of anilines occurs through a "borrowing hydrogen" reaction. Notably, this reaction is highly selective for the monomethylated product.