Ethanol Upgrading with N,N,N-Pincer-Based Ru Catalysts: Delineating Key Factors Governing Catalyst Evolution and Stability

• Published in: ACS catalysis Vol. 14; no. 11; pp. 8456 - 8462
• Main Authors: Farris, Benjamin M., Davies, Alex M., Stephenson, Corey R. J., Szymczak, Nathaniel K.
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 15-05-2024; American Chemical Society (ACS)
• Subjects: (de)hydrogenation; 09 BIOMASS FUELS; alcohols; catalysts; chemical reactions; decarbonylation; ethanol; Guerbet; ligands; ruthenium; Guerbet; ruthenium; (de)hydrogenation; decarbonylation; ethanol
• ISSN: 2155-5435; 2155-5435
• DOI: 10.1021/acscatal.4c01361

The 5-CH3-bpi (bpi = 1,3-bis­(2′-pyridylimino)­isoindolate) ruthenium catalyst is among the most active catalysts to generate higher order alcohols from ethanol, via the Guerbet reaction, yet the reason(s) for this beneficial CH3-subsitution position (5- relative to 4- and 6-) were not known. To understand the influence of this unique positional activity, we report a mechanistic investigation of the N,N,N-pincer Ru­(bpi)­(PPh3)2Cl catalyst. In situ IR and ex situ NMR/ESI-MS analyses of catalytic reactions identified a series of Ru carbonyl species generated during catalysis. We find that the primary decomposition pathway is via hydrogenolysis of the bpi ligands and that incorporating a methyl group at the 5-position disfavors this deactivation pathway.