Journal article
Mechanistic Investigation of the Ruthenium–N-Heterocyclic-Carbene-Catalyzed Amidation of Alcohols and Amines
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.
Language: | English |
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Publisher: | WILEY‐VCH Verlag |
Year: | 2012 |
Pages: | 15683-15692 |
ISSN: | 15213765 and 09476539 |
Types: | Journal article |
DOI: | 10.1002/chem.201202400 |
ORCIDs: | Fristrup, Peter and Madsen, Robert |