We describe herein mechanistic studies of ester hydrogenation catalyzed by CNN- and PNN-pincer complexes of ruthenium, where the pincer ligands feature dialkylamino side groups. When heated in the presence of a phosphine ligand, the ruthenium(II) precatalysts undergo an unexpected dehydroalkylation reaction, releasing an equivalent of ethane or propane to form five-coordinate ruthenium(0) complexes featuring a nascent imine functional group. The ruthenium(0) complexes are kinetically competant as catalysts, and in some cases give much faster ester hydrogenation catalysis. We present evidence that the dehydroalkylation reaction is a necessary prerequisite for catalysis, and that the ruthenium(0)-imine complexes react under the catalytic conditions with two equivalents of hydrogen to give ruthenium(II)-complexes featuring an N-H functional group, which we propose are the actual catalytic intermediates. These findings have potentially broad implications for the mechansims of metal-ligand-cooperative hydrogenations and dehydrogenations of polar bonds.

Dehydroaylkative catalyst activation of CNN- and PNN-pincer-ruthenium catalysts for ester hydrogenation

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.