State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, 130022, P. R. China.
Dalton Trans. 2010 Jun 14;39(22):5377-87. doi: 10.1039/b926098f. Epub 2010 May 10.
Density functional theory (DFT) calculations have been performed to investigate the alcohol oxidation to acetaldehyde catalyzed by the Cu-bipy (bipy = 2,2'-bipyridine) catalyst with and without TEMPO (TEMPO stands for 2,2,6,6-tetramethylpiperidinyloxy). In the presence of TEMPO, two mechanisms are proposed, which are (1) TEMPO and the alcohol coordinate to the Cu center and react in the coordination sphere, and (2) the formation of the nitronium cation. On the basis of our calculations, the nitronium cation mechanism can be ruled out. For the case without TEMPO, it is found that the change of the Cu oxidation states (Cu(II) <--> Cu(I)) plays an important role in assisting the catalytic reaction cycle, while the O(2) molecule assists the formation of the product acetaldehyde. In addition, the overall activation barrier with TEMPO is preferred over the pathway without TEMPO by 5.2 kcal mol(-1). This is consistent with the experimental observation that the Cu-bipy catalyst in the absence of TEMPO is less efficient when compared with that in the presence of TEMPO. The difference in mechanism is discussed tentatively based on the molecular orbitals.
密度泛函理论（DFT）计算已被用于研究 Cu-bipy（bipy=2,2'-联吡啶）催化剂存在和不存在 TEMPO（TEMPO 代表 2,2,6,6-四甲基哌啶氧自由基）时对醇氧化为乙醛的催化作用。在 TEMPO 的存在下，提出了两种机制，即（1）TEMPO 和醇与 Cu 中心配位并在配位球中反应，和（2）形成硝鎓阳离子。根据我们的计算，可以排除硝鎓阳离子机制。对于没有 TEMPO 的情况，发现 Cu 氧化态（Cu(II) <--> Cu(I)）的变化在辅助催化反应循环中起着重要作用，而 O(2)分子辅助产物乙醛的形成。此外，与没有 TEMPO 的途径相比，有 TEMPO 时的整体活化能垒更优选 5.2 kcal mol(-1)。这与实验观察结果一致，即与存在 TEMPO 时相比，Cu-bipy 催化剂在不存在 TEMPO 时效率较低。根据分子轨道，我们初步讨论了机制上的差异。
