基于密度泛函理论及实验揭示pincer钯催化偶联反应机理

On Mechanism of Pincer Palladium Catalyzed Coupling Reaction Based on DFT Theory and Experiment

使用系统的密度泛函理论(density functional theory, DFT)和化学实验的方法来揭示NCN-pincer钯催化Suzuki偶联反应的机理.通过单晶衍射确定了NCN-pincer配合物的化学空间结构,从而构建其Suzuki偶联反应中的催化剂空间结构的计算模型,用密度泛函理论的B3LYP泛函完成了所有计算,找到了pincer钯不同形态对卤带芳烃氧化加成的过渡态,理论计算所得到的结果与实验结果相一致.另一方面单独的pincer钯和加入碘代芳烃后的pincer钯分别置于二氧六环回流,相同指定间隔时间内取样做MS分析,证明了增加底物量能有效的提高催化剂的催化活性.同时先期计算得出NCN-pincer钯催化Suzuki偶联反应的机理:①NCN-pincer钯失去溴;②氧化加成;③转金属化;④还原消除释放催化剂的过程,而实验中的现象也对此进行了有效的印证.

DFT calculations and some chemical experiments have been applied to explore the mechanism of NCN palladium complexes-catalyzed Suzuki-Miyaura coupling reaction. Single-crystal diffraction determined complex chemical spatial structure of the NCN pincer-Pd, subsequently we build the model of catalyst spatial structure in Suzuki-Miyaura coupling reaction and completed all calculations by using B3 LYP. At the same time, the transition states, existing in oxidative addition of PhX that was catalyzed by the different NCN type of pincer-Pd were observed, excitedly, the results of a DFT investigation were consistent with that of MS. On the other hand, pincer-Pd complexes and pincer-Pd complexes with PhI respectively refluxed with dioxane, MS analysis showed increasing substrate could effectively improve the activity of the catalyst. Based on calculations, NCN-pincer palladium-catalyzed Suzuki coupling reaction had four steps: ① NCN-pincer palladium lost bromine;② oxidative addition;③ transfer metallization;④ reductive elimination process releases the catalyst. In the same way, the experimental result have demonstrated above mechanism. In conclusion, this could provide a theoretical basis for chemists to design better catalysts.