CNN pincer ruthenium catalysts for hydrogenation and transfer hydrogenation of ketones: Experimental and computational studies

Walter Baratta, Salvatore Baldino, Maria José Calhorda, Paulo J. Costa, Gennaro Esposito, Eberhardt Herdtweck, Santo Magnolia, Carlo Mealli, Abdelatif Messaoudi, Sax A. Mason, Luis F. Veiros

Research output: Contribution to journalArticle

Abstract

Reaction of [RuCl(CNN)(dppb)] (1-Cl) (HCNN=2-aminomethyl-6-(4-methylphenyl)pyridine; dppb=Ph2P(CH2)4PPh2) with NaOCH2CF3 leads to the amine-alkoxide [Ru(CNN)(OCH2CF3)(dppb)] (1-OCH2CF3), whose neutron diffraction study reveals a short RuO⋯HN bond length. Treatment of 1-Cl with NaOEt and EtOH affords the alkoxide [Ru(CNN)(OEt)(dppb)]·(EtOH)n (1-OEt·n EtOH), which equilibrates with the hydride [RuH(CNN)(dppb)] (1-H) and acetaldehyde. Compound 1-OEt·n EtOH reacts reversibly with H2 leading to 1-H and EtOH through dihydrogen splitting. NMR spectroscopic studies on 1-OEt·n EtOH and 1-H reveal hydrogen bond interactions and exchange processes. The chloride 1-Cl catalyzes the hydrogenation (5 atm of H2) of ketones to alcohols (turnover frequency (TOF) up to 6.5×104 h-1, 40 C). DFT calculations were performed on the reaction of [RuH(CNN′)(dmpb)] (2-H) (HCNN′=2-aminomethyl-6-(phenyl)pyridine; dmpb=Me2P(CH2)4PMe2) with acetone and with one molecule of 2-propanol, in alcohol, with the alkoxide complex being the most stable species. In the first step, the Ru-hydride transfers one hydrogen atom to the carbon of the ketone, whereas the second hydrogen transfer from NH2 is mediated by the alcohol and leads to the key "amide" intermediate. Regeneration of the hydride complex may occur by reaction with 2-propanol or with H2; both pathways have low barriers and are alcohol assisted.

Original languageEnglish (US)
Pages (from-to)13603-13617
Number of pages15
JournalChemistry - A European Journal
Volume20
Issue number42
DOIs
StatePublished - Oct 1 2014

Keywords

  • alkoxides
  • density functional theory
  • hydrogen transfer
  • hydrogenation
  • ruthenium

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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    Baratta, W., Baldino, S., Calhorda, M. J., Costa, P. J., Esposito, G., Herdtweck, E., Magnolia, S., Mealli, C., Messaoudi, A., Mason, S. A., & Veiros, L. F. (2014). CNN pincer ruthenium catalysts for hydrogenation and transfer hydrogenation of ketones: Experimental and computational studies. Chemistry - A European Journal, 20(42), 13603-13617. https://doi.org/10.1002/chem.201402229