College of Chemistry, Beijing Normal University, Beijing 100875, China.
Org Biomol Chem. 2015 Aug 7;13(29):7950-60. doi: 10.1039/c5ob01118c. Epub 2015 Jun 25.
Due to its green-chemistry advantages, the dehydrogenative Heck reaction (DHR) has experienced enormous growth over the past few decades. In this work, two competing reaction channels were comparatively studied for the Pd(OAc)2-catalyzed DHRs of arenes with alkenes, referred to herein as the arene activation mechanism and the alkene activation mechanism, respectively, which mainly differ in the involvement of the reactants in the C-H activation step. Our calculations reveal that the commonly accepted arene activation mechanism is plausible for the desired arene-alkene cross-coupling; in contrast, the alternative alkene activation mechanism is kinetically inaccessible for the desired cross-coupling, but it is feasible for the homo-coupling of alkenes. The nature of directing groups on reactants could mainly determine the dominance of the two competing reaction routes, and therefore, influence the experimental yields. A wide range of directing groups experimentally used are examined by the density functional theory (DFT) method in this work, providing theoretical guidance for screening compatible reactants.
由于其绿色化学优势，脱氢 Heck 反应（DHR）在过去几十年中经历了巨大的发展。在这项工作中，分别称为芳环活化机制和烯烃活化机制，对 Pd(OAc)2 催化的芳环与烯烃的 DHR 中两种竞争反应途径进行了比较研究，它们主要区别在于反应物在 C-H 活化步骤中的参与。我们的计算表明，通常接受的芳环活化机制对于所需的芳基-烯烃交叉偶联是合理的；相比之下，替代的烯烃活化机制对于所需的交叉偶联在动力学上是不可行的，但对于烯烃的同偶联是可行的。反应物上的导向基团的性质主要决定了两种竞争反应途径的主导地位，从而影响实验产率。这项工作通过密度泛函理论（DFT）方法对实验中使用的广泛的导向基团进行了检验，为筛选相容的反应物提供了理论指导。
