Zhao Dan, Li Xiaoxi, Han Keli, Li Xingwei, Wang Yong
†School of Chemistry, Dalian University of Technology, Dalian 116024, People's Republic of China.
‡State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, People's Republic of China.
J Phys Chem A. 2015 Mar 26;119(12):2989-97. doi: 10.1021/jp511564b. Epub 2015 Mar 6.
The reaction mechanism of Rh(III)-catalyzed cross-dehydrogenative aryl-aryl coupling between benzamides and haloarenes was investigated through detailed density functional theoretical (DFT) studies in terms of regioselectivity and deuterium kinetic isotope effects (KIEs). Three possible routes including one PivO(-)-assisted reaction route and two non-PivO(-)-assisted reaction routes have been studied. The calculated results refute the proposed mechanism (without PivO(-)-assisted process) in the experimental paper and demonstrate that the PivO(-)-assisted reaction mechanism is the most favored. Meanwhile, the calculation revealed that the PivO(-) anion plays a crucial role as a proton acceptor in the C-H bond activation, especially when the second C-H activation of haloarenearene proceeds via a S(E)3 mechanism. The S(E)3 mechanism is presented for the Rh(III)-catalyzed aryl-aryl reaction for the first time. Our mechanism is evaluated by the calculations of the para-/meta-regioselectivity and KIEs. And it is found that the second activation process is the rate-determining step of the whole catalytic cycle. All these calculated properties agree well with the experiment and Glorius's proposal that the Rh(III)-catalyzed cross-dehydrogenative C-C coupling reaction proceeds by dual C-H activations. Our theoretical studies suggest that the Rh(III) complex catalyst strongly affects the mechanisms of the second C-H activation step and thus this work might provide insight into the design of new catalytic systems.
通过详细的密度泛函理论（DFT）研究，从区域选择性和氘动力学同位素效应（KIEs）方面对铑（III）催化的苯甲酰胺与卤代芳烃之间的交叉脱氢芳基-芳基偶联反应机理进行了研究。研究了三条可能的途径，包括一条PivO(-)辅助反应途径和两条非PivO(-)辅助反应途径。计算结果驳斥了实验论文中提出的机理（无PivO(-)辅助过程），并表明PivO(-)辅助反应机理是最有利的。同时，计算表明PivO(-)阴离子在C-H键活化中作为质子受体起着关键作用，特别是当卤代芳烃的第二次C-H活化通过S(E)3机理进行时。首次提出了用于铑（III）催化的芳基-芳基反应的S(E)3机理。通过对位/间位区域选择性和KIEs的计算对我们的机理进行了评估。并且发现第二个活化过程是整个催化循环的速率决定步骤。所有这些计算性质与实验以及Glorius提出的铑（III）催化的交叉脱氢C-C偶联反应通过双重C-H活化进行的观点非常吻合。我们的理论研究表明，铑（III）配合物催化剂强烈影响第二个C-H活化步骤的机理，因此这项工作可能为新催化体系的设计提供见解。
