Alcohol-assisted base-free hydrogenation of acetophenone catalyzed by OsH(NHCMe2CMe2NH2)(PPh3)2

Sean E. Clapham, Marco Zimmer De Iuliis, Katharina Mack, Demyan E. Prokopchuk, Robert H. Morris

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

The hydrido-amido complex OsH(NHCMe2CMe2NH 2)(PPh3)2 (1) catalyzes the base-free hydrogenation of ketones in benzene. Kinetic studies using acetophenone revealed that the system has an induction period, after which the rate of the reaction increases. A constant rate was observed when a critical amount of the product alcohol was added, indicating that the reaction is autocatalytic in 1-phenylethanol. Varying the initial conditions showed that the reaction rate is dependent on hydrogen and catalyst concentration and independent of ketone concentration. Above the critical concentrations of 1-phenylethanol, the reaction rate is independent of alcohol concentration. The rate law for pressures up to 5 atm was found to be rate = d[alcohol]/dt = -d[ketone]/dt = k[Os][H2], with k = 30 mol L-1s-1 at 293 K and the temperature dependence provided energy of activation parameters. Therefore, the heterolytic splitting of dihydrogen is rate determining under these conditions. Only small kinetic isotope effects were measured in contrast with the analogous ruthenium system. Complex 1 reacts with the product alcohol 1-phenylethanol and is partially converted into the dihydride complex trans-OsH2(NH2CMe2CMe2NH 2)(PPh3)2 and acetophenone; with excess alcohol, an osmium alkoxide is observed at low temperature. As expected from these results, 1 is a ketone transfer hydrogenation catalyst in isopropanol.

Original languageEnglish (US)
Pages (from-to)731-738
Number of pages8
JournalCanadian Journal of Chemistry
Volume92
Issue number8
DOIs
StatePublished - Aug 2014
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Organic Chemistry

Keywords

  • Autocatalysis
  • Catalytic hydrogenation
  • Hydride
  • Isotope effect
  • Ketone
  • Osmium complex

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