Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 23, Issue 6, Pages 1368-1378Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201604402
Keywords
copper; density functional calculations; homogeneous catalysis; oxidation; reaction mechanisms
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Funding
- Israel Science Foundation Individual Research Grant [1914/15]
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Identifying the mechanism of a catalytic reaction is paramount for designing new and improved catalysts. Several alternative catalytic cycles for the copper/2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO)-catalyzed aerobic oxidation of alcohols to the corresponding aldehydes or ketones were examined using DFT at the SMD(CH3CN)-RIJCOSX-DSDPBEB95/def2-TZVP//DF-PBED3BJ/def2-SVP level of theory. A catalytic cycle in which TEMPO remains coordinated to copper throughout was identified as the most likely mecha-nism. There are three components to the catalytic cycle: 1) hydrogen transfer from the alkoxyl ligand to coordinated TEMPO, 2) oxygen activation with formation of a peroxo complex, and 3) alcohol activation with transfer of the OH proton to the peroxo ligand. The oxidation takes place via a six-membered intramolecular hydrogen-transfer transition state. Importantly, this is not the rate-determining step, which instead involves oxygen activation and/or the initial alcohol activation.
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