Zhong Ziying, Li Qingzhong, Li Xiaoyan
College of Chemistry and Material Science, Hebei Key Laboratory of Inorganic and Nano-Materials, National Demonstration Center for Experimental Chemistry, Hebei Normal University, Shijiazhuang, 050024, P. R. China.
The Laboratory of Theoretical and Computational Chemistry, College of Chemistry& Chemical Engineering, Yantai University, Yantai, 264005, China.
Phys Chem Chem Phys. 2024 Sep 18;26(36):24058-24067. doi: 10.1039/d4cp02576h.
The dirhodium(II) complexes with bridging phosphine and OAc ligands showed high reactivity and selectivities in olefin dehydrosilylation. In order to determine the structure of the actual catalyst which cannot be determined experimentally, the geometries of the dirhodium catalyst, the detailed catalytic mechanism, and the stereo- and chemo-selectivities of the title reaction were studied using DFT calculations. The results showed that one OAc group is monodentate and the other is bidentate in the dirhodium catalyst C'. The determined catalytic cycle consists of four processes: Rh-H bond activation in C', Si-H bond activation in alkoxysilane, alkylene insertion into the Rh-Si bond, followed by β-H elimination or σ-metathesis reaction. Among them, the alkylene insertion process is the rate-determining step. The stereoselectivity of the title reaction is controlled by the steric effect and orbital interactions between the alkyene and dirhodium catalysts in the β-H elimination process. The chemoselectivity is regulated by the presence of the axial ligand in the dirhodium catalyst, when there is an axial ligand coordinated to the Rh atom, -alkene is the main product, whereas alkane would be obtained in the absence of an axial ligand. Our work determines the structure of the actual catalyst, and provides explanations and predictions for the activity, and chemo- and stereo-selectivity control of olefin dehydrosilylation.
含桥连膦和乙酸根配体的二铑（II）配合物在烯烃脱氢硅基化反应中表现出高反应活性和选择性。为了确定无法通过实验测定的实际催化剂的结构，使用密度泛函理论（DFT）计算研究了二铑催化剂的几何结构、详细的催化机理以及该反应的立体和化学选择性。结果表明，在二铑催化剂C'中，一个乙酸根基团为单齿配位，另一个为双齿配位。确定的催化循环包括四个过程：C'中Rh-H键的活化、烷氧基硅烷中Si-H键的活化、亚烷基插入Rh-Si键，随后是β-H消除或σ-复分解反应。其中，亚烷基插入过程是速率决定步骤。该反应的立体选择性在β-H消除过程中受空间效应以及烯烃与二铑催化剂之间的轨道相互作用控制。化学选择性由二铑催化剂中轴向配体的存在调节，当有轴向配体与Rh原子配位时，烯烃是主要产物，而在没有轴向配体时则会得到烷烃。我们的工作确定了实际催化剂的结构，并对烯烃脱氢硅基化反应的活性、化学和立体选择性控制提供了解释和预测。
