School of Chemistry and Chemical Engineering, Chongqing Key Laboratory of Theoretical and Computational Chemistry, Chongqing University, Chongqing, 400030, China.
College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou, 450001, China.
Chem Asian J. 2019 Mar 1;14(5):655-661. doi: 10.1002/asia.201801862. Epub 2019 Feb 13.
Palladium (Pd)-catalyzed radical oxidative C-H carbonylation of alkanes is a useful method for functionalizing hydrocarbons, but there is still a lack of understanding of the mechanism, which restricts the application of this reaction. In this work, density functional theory (DFT) calculations were carried out to study the mechanism for a Pd-catalyzed radical esterification reaction. Two plausible reaction pathways have been proposed and validated by DFT calculations. The computational results reveal that the generated alkyl radical prefers to add to the carbon monoxide (CO) molecule to form a carbonyl radical before bonding with the Pd species. Radical addition onto Pd followed by CO migratory insertion was unfavorable owing to the high energy barrier of the migratory insertion step. The regioselectivity of the C(sp )-H carbonylation was also investigated by DFT. The results show that the regioselectivity is controlled by both the bond dissociation energy of the reacting C-H bond and the stability of the corresponding generated carbon radical. Competitive side reactions also affected the yield and regioselectivity owing to the rapid consumption of the stable radical intermediate.
钯（Pd）催化的烷烃自由基氧化 C-H 羰基化反应是一种用于功能化烃类的有用方法，但对其反应机理仍缺乏了解，这限制了该反应的应用。在这项工作中，我们通过密度泛函理论（DFT）计算研究了 Pd 催化的自由基酯化反应的机理。通过 DFT 计算提出并验证了两种可能的反应途径。计算结果表明，生成的烷基自由基在与 Pd 物种键合之前，更倾向于与一氧化碳（CO）分子加成形成羰基自由基。由于迁移插入步骤的能垒较高，烷基自由基加成到 Pd 上然后 CO 迁移插入是不利的。通过 DFT 还研究了 C(sp3)-H 羰基化的区域选择性。结果表明，区域选择性既受反应 C-H 键的键离能的控制，也受相应生成的碳自由基的稳定性的控制。由于稳定自由基中间体的快速消耗，竞争性副反应也会影响产率和区域选择性。
