A mechanistic study of the manganese porphyrin-catalyzed C-H isocyanation reaction
A mechanistic study of the manganese porphyrin-catalyzed C-H isocyanation reaction
复制标题
锰卟啉催化C-H异氰化反应的机理研究
DOI：
10.1039/d0qo01442g
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发表时间：
2021
影响因子：
5.4
通讯作者：
She Yuan-Bin
中科院分区：
文献类型：
--
作者：
Liu Ning;Chen Xiahe;Jin Liyuan;Yang Yun-Fang;She Yuan-Bin
用密度泛函理论(DFT)方法探讨了锰卟啉催化的脂肪族C-H异氰化反应的机理和化学选择性的来源。在该反应中，通过氢提取过程形成了羟基锰卟啉和底物衍生自由基的双自由基中间体络合物。然后，OH与NCO的轴向配体交换生成二异氰酸酯锰卟啉中间体，这为NCO反弹反应生成烷基异氰酸酯提供了可能。不同轴向配体反弹到底物衍生自由基的竞争是不同产物的来源。计算结果表明，NCO-反弹途径比OH-反弹途径有利2.7kcal−-1，这与实验结果一致，即主要产物是烷基异氰酸酯而不是氧化产物。由于轴向配体NCO的反式作用强于OH，因此通过二异氰酸酯锰卟啉中间体的NCO反弹途径比通过羟基锰卟啉的NCO反弹途径有利5.9kcal−1。我们还发现，给电子的芳基配体可以促进C-H键异氰化反应。该反应机理和控制因素同样适用于锰卟啉催化的C-H键叠氮化反应。
We explored the mechanism and the origin of chemoselectivity of the manganese porphyrin-catalyzed aliphatic C–H isocyanation reaction with density functional theory (DFT) calculations. In this reaction, a diradical intermediate complex of a hydroxomanganese porphyrin and a substrate-derived radical is formed by the H-abstraction process. Then the axial ligand exchange of OH with NCO leads to a di-isocyanate manganese porphyrin intermediate, which provides the possibility for the NCO-rebound process to form the alkyl isocyanate product. The competition of different axial ligands rebounding to substrate-derived radicals is the origin of different products. The computational results suggest that the NCO-rebound pathway is more favorable than the OH-rebound pathway by 2.7 kcal mol−1, which is consistent with the experimental results that the major product is an alkyl isocyanate instead of the oxygenation product. The NCO-rebound pathway through the di-isocyanate manganese porphyrin intermediate is more favorable than that through the hydroxomanganese porphyrin by 5.9 kcal mol−1 due to the stronger trans effect of the axial ligand NCO compared to OH. We also found that the electron-donating aryl ligand can promote the C–H bond isocyanation. The mechanism and the controlling factors are also applicable to the manganese porphyrin-catalyzed C–H bond azidation reaction.