C-H键活化反应的密度泛函理论模拟对简化模型的评估

采用密度泛函理论方法, 模拟了Rh(PPh₃)₃Cl催化的C-H键活化/C-C键偶联反应. 将反应机理分为C-H键活化、 迁移插入和还原消除3个过程进行讨论. 计算结果表明, 势能面的最高点为迁移插入的过渡态, 相对于初始原料的自由能为108.3 kJ/mol. 为了探索简化计算模型对模拟反应机理的影响, 使用2种模型催化剂Rh(PMe₃)₃Cl和Rh(PH₃)₃Cl表征相同的反应过程, 结果表明配体简化模型不合理, 主要是因为PPh₃配体的空间效应和熵效应非常明显.

Density Functional Theoritical Studies on Catalytic C-H Activation Reaction: Problem of Truncated Model†

Density functional theory method was employed to simulate a Rh(PPh₃)₃Cl catalyzed C-H activation/C-C cross-coupling reaction, in which three typical processes, namely, C-H activation, migratory insertion and reductive elimination, were characterized. The obtained results show that the rate-determining step is migratory insertion with the free-energy barrier of 108.3 kJ/mol. In order to test the validation of truncated models, two small catalysts Rh(PMe₃)₃Cl and Rh(PH₃)₃Cl were also used to study the same coupling reaction. Our calculations suggested that truncated models led to misunderstanding of reaction mechanism and free-energy changes, especially for migratory insertion process, since the steric effect and entropic contribution play a great role on these types of reactions.