Iron Mark A, Szpilman Alex M
Computational Chemistry Unit, Department of Chemical Research Support, Weizmann Institute of Science, 7610001, Rehovot, Israel.
Department of Chemical Sciences, Ariel University, 40700, Ariel, Israel.
Chemistry. 2017 Jan 26;23(6):1368-1378. doi: 10.1002/chem.201604402. Epub 2016 Dec 27.
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(CH CN)-RIJCOSX-DSD-PBEB95/def2-TZVP//DF-PBE /def2-SVP level of theory. A catalytic cycle in which TEMPO remains coordinated to copper throughout was identified as the most likely mechanism. 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.
确定催化反应的机制对于设计新型且性能更优的催化剂至关重要。使用密度泛函理论（DFT），在SMD(CH₃CN)-RIJCOSX-DSD-PBEB95/def2-TZVP//DF-PBE /def2-SVP理论水平下，研究了铜/2,2,6,6-四甲基哌啶-N-氧基（TEMPO）催化醇类有氧氧化为相应醛或酮的几种替代催化循环。一种TEMPO始终与铜配位的催化循环被确定为最可能的机制。该催化循环有三个组成部分：1）氢从烷氧基配体转移至配位的TEMPO；2）通过形成过氧配合物进行氧活化；3）通过将OH质子转移至过氧配体进行醇活化。氧化反应通过六元分子内氢转移过渡态发生。重要的是，这并非速率决定步骤，速率决定步骤反而涉及氧活化和/或初始醇活化。
