Mechanism of C-H bond activation/C-C bond formation reaction between diazo compound and alkane catalyzed by dirhodium tetracarboxylate
Mechanism of C-H bond activation/C-C bond formation reaction between diazo compound and alkane catalyzed by dirhodium tetracarboxylate
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DOI：
10.1021/ja017823o
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发表时间：
2002-06-19
影响因子：
15
通讯作者：
Yamanaka, M
中科院分区：
文献类型：
--
作者：
Nakamura, E;Yoshikai, N;Yamanaka, M
采用密度泛函B3 LYP方法研究了重氮化合物与烷烃的C-H键活化/C-C键形成反应，揭示了催化循环中重要中间体和过渡态的能量学和几何构型.该反应通过铑催化剂和重氮化合物之间的络合引发。在Rh 4d（xz）轨道向C-N sigma*-轨道的反馈驱动下，发生氮挤出以提供铑-卡宾络合物。配合物的卡宾碳是强亲电的，因为它的空2 p轨道。C-H活化/C-C形成通过具有小活化能的三中心氢化物转移样过渡态在单一步骤中进行。两个铑原子中只有一个在整个反应中作为卡宾结合位点，另一个铑原子协助C-H插入反应。第二个Rh原子充当第一个Rh原子的移动的配体，以增强卡宾部分的亲电性并促进铑-碳键的裂解。计算再现了实验数据，包括氮挤出的活化焓，C-H插入的动力学同位素效应，和C-H键的反应性顺序。
The B3LYP density functional studies on the dirhodium tetracarboxylate-catalyzed C-H bond activation/C-C bond formation reaction of a diazo compound with an alkane revealed the energetics and the geometry of important intermediates and transition states in the catalytic cycle. The reaction is initiated by complexation between the rhodium catalyst and the diazo compound. Driven by the back-donation from the Rh 4d(xz) orbital to the C-N sigma*-orbital, nitrogen extrusion takes place to afford a rhodium-carbene complex. The carbene carbon of the complex is strongly electrophilic because of its vacant 2p orbital. The C-H activation/C-C formation proceeds in a single step through a three-centered hydride transfer-like transition state with a small activation energy. Only one of the two rhodium atoms works as a carbene binding site throughout the reaction, and the other rhodium atom assists the C-H insertion reaction. The second Rh atom acts as a mobile ligand for the first one to enhance the electrophilicity of the carbene moiety and to facilitate the cleavage of the rhodium-carbon bond. The calculations reproduce experimental data including the activation enthalpy of the nitrogen extrusion, the kinetic isotope effect of the C-H insertion, and the reactivity order of the C-H bond.