Liu Jian-Biao, Tian Ying-Ying, Zhang Xin, Wang Lu-Lin, Chen De-Zhan
College of Chemistry, Chemical Engineering and Materials Science, Collaborative Innovation Center of Functionalized Probes for Chemical Imaging in Universities of Shandong, Key Laboratory of Molecular and Nano Probes, Ministry of Education, Institute of Molecular and Nano Science, Shandong Normal University, Jinan 250014, P. R. China.
Dalton Trans. 2018 Apr 3;47(14):4893-4901. doi: 10.1039/C8DT00015H.
The detailed mechanism of palladium-catalyzed γ-C(sp3)-H olefination/cyclization of triflyl-protected amines was investigated by density functional theory (DFT) calculations. The olefinated intermediate was initially formed in the first catalytic cycle involving ligand exchange, bicarbonate-assisted C(sp3)-H bond cleavage, alkene insertion and 'reductive β-hydride elimination'. The following syn-addition and reductive elimination furnish the aza-Wacker product. The first step of reductive elimination is the rate-determining step. The mechanism unveils the important roles of bicarbonate: aiding the C-H activation and abstracting the β-proton in the second step of reductive elimination. The parallel bridging mode in the metal-olefin intermediate facilitates the syn-addition, explaining the experimentally observed stereoselectivity. The effect of the monodentate pyridine-based ligands is also discussed.
通过密度泛函理论（DFT）计算研究了钯催化的三氟甲磺酸酯保护胺的γ-C(sp3)-H烯基化/环化反应的详细机理。在第一个催化循环中，涉及配体交换、碳酸氢盐辅助的C(sp3)-H键裂解、烯烃插入和“还原β-氢化物消除”，最初形成了烯基化中间体。随后的顺式加成和还原消除生成氮杂瓦克产物。还原消除的第一步是速率决定步骤。该机理揭示了碳酸氢盐的重要作用：在还原消除的第二步中帮助C-H活化并夺取β-质子。金属-烯烃中间体中的平行桥连模式促进了顺式加成，解释了实验观察到的立体选择性。还讨论了单齿吡啶基配体的影响。
