Mechanistic Investigation of the Ruthenium–N-Heterocyclic-Carbene-Catalyzed Amidation of Alcohols and Amines

Publication: Research - peer-reviewJournal article – Annual report year: 2012

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The mechanism of the ruthenium–N-heterocyclic-carbene-catalyzed formation of amides from alcohols and
amines was investigated by experimental techniques (Hammett studies, kinetic isotope effects) and by a computational study by using dispersion-corrected density functional theory (DFT/
M06). The Hammett study indicated that a small positive charge builds-up at the benzylic position in the transition
state of the turnover-limiting step. The kinetic isotope effect was determined to be 2.29ACHTUNGTRENUNG(!0.15), which suggests that the breakage of the C"H bond is not the rate-limiting step, but that it is one of several slow steps in the catalytic cycle. Rapid scrambling of hydrogen and deuterium at the a position of the alcohol was observed with
deuterium-labeled substrates, which implies that the catalytically active species is a ruthenium dihydride. The experimental results were supported by the characterization of a plausible catalytic cycle by using DFT/M06. Both cisdihydride and trans-dihydride intermediates were considered, but when the theoretical turnover frequencies
(TOFs) were derived directly from the calculated DFT/M06 energies, we found that only the trans-dihydride
pathway was in agreement with the experimentally determined TOFs.
Original languageEnglish
JournalChemistry: A European Journal
Publication date2012
Number of pages11
ISSN0947-6539
DOIs
StateAccepted
CitationsWeb of Science® Times Cited: 8

Keywords

  • Amides, Density functional calculations, Isotope effect, Reaction mechanisms, Ruthenium
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