Mechanistic Insights into Palladium-Catalyzed Silylation of Aryl Iodides with Hydrosilanes through a DFT Study.
Mechanistic Insights into Palladium-Catalyzed Silylation of Aryl Iodides with Hydrosilanes through a DFT Study.
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DOI：
10.1002/asia.201700174
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发表时间：
2017-07
期刊：
影响因子：
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通讯作者：
Zheng Xu;Jinzhou Xu;Jin Zhang;Zhanjiang Zheng;Jian Cao;Yu-Ming Cui;Li‐Wen Xu
中科院分区：
文献类型：
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作者：
Zheng Xu;Jinzhou Xu;Jin Zhang;Zhanjiang Zheng;Jian Cao;Yu-Ming Cui;Li‐Wen Xu
采用杂化密度泛函理论（DFT）研究了钯催化芳基碘硅烷化反应的催化循环，该反应是由氢硅烷或芳基碘的氧化加成引发的，通过三种不同的反应机理，即R3 Si-PdII -H（循环A）、Ar-PdII -I（循环B）和PdIV（循环C）.计算表明，反应的化学选择性和反应性取决于催化剂的连接状态和特定的反应条件，包括底物的进料顺序和碱的存在。对于体积较小的双配位催化剂，循环C在能量上优于循环A，通过循环A，甲硅烷基化过程略微优于还原过程。有趣的是，对于大体积单配体催化剂，循环B在能量上比普遍接受的循环A更有利，其中甲硅烷基化通道与还原通道相比略微不利。此外，在该通道中包含碱允许甲硅烷基化产物成为主导。这些发现为复杂的实验观察提供了很好的解释。因此建议设计一种反应方法，其允许钯（0）络合物与芳基碘的氧化加成在与氢硅烷的氧化加成之前发生，以通过促进催化循环通过循环B（单配体Pd 0催化剂）或C（双配体Pd 0催化剂）而不是循环A进行来改善甲硅烷基化产物的反应性和化学选择性。
The catalytic cycles of palladium-catalyzed silylation of aryl iodides, which are initiated by oxidative addition of hydrosilane or aryl iodide through three different mechanisms characterized by intermediates R3 Si-PdII -H (Cycle A), Ar-PdII -I (Cycle B), and PdIV (Cycle C), have been explored in detail by hybrid DFT. Calculations suggest that the chemical selectivity and reactivity of the reaction depend on the ligation state of the catalyst and specific reaction conditions, including feeding order of substrates and the presence of base. For less bulky biligated catalyst, Cycle C is energetically favored over Cycle A, through which the silylation process is slightly favored over the reduction process. Interestingly, for bulky monoligated catalyst, Cycle B is energetically more favored over generally accepted Cycle A, in which the silylation channel is slightly disfavored in comparison to that of the reduction channel. Moreover, the inclusion of base in this channel allows the silylated product become dominant. These findings offer a good explanation for the complex experimental observations. Designing a reaction process that allows the oxidative addition of palladium(0) complex to aryl iodide to occur prior to that with hydrosilane is thus suggested to improve the reactivity and chemoselectivity for the silylated product by encouraging the catalytic cycle to proceed through Cycles B (monoligated Pd0 catalyst) or C (biligated Pd0 catalyst), instead of Cycle A.