Distinct Catalytic Performance of Dirhodium(II) Complexes with <i>ortho</i>-Metalated DPPP in Dehydrosilylation of Styrene Derivatives with Alkoxysilanes

Herein, we describe dirhodium­(II) complexes for the ortho-metalated 1,3-bis(diphenylphosphino)­propane (DPPP)-catalyzed dehydrosilylation of vinylarenes with tertiary silanes, particularly alkoxysilanes. This catalytic method displays a broad substrate scope. Both electron-donating and electron-withdrawing substituents on the vinylarenes are well tolerated in this protocol. The dehydrosilylation reactions are compatible with a diverse range of tertiary silanes such as (EtO)3SiH, (TMSO)2MeSiH, (HSiMe2)2O, Et3SiH, and Ph3SiH. Mechanistic studies indicated that a mixture of Rh2(OAc)4, DPPP, and P­(OMe)3 provided a stable and rigid dirhodium­(II) complex with ortho-metalated DPPP as the bridging ligand and the phosphonate as the axial ligand in the catalytic system. The structure of the dirhodium­(II) complexes was also supported by X-ray crystal diffraction. Further experiments confirmed that the dirhodium­(II) complexes may be the active species that catalyze the dehydrosilylation reaction. Control experiments showed that norbornene works as the hydrogen acceptor in the reaction and plays a crucial role in the generation of the key catalytic intermediate, a rhodium silicon species.本文报道了一类用于邻位金属化1,3-双(二苯基膦基)丙烷（1,3-bis(diphenylphosphino)propane，DPPP）催化的乙烯基芳烃与叔硅烷（尤其是烷氧基硅烷）脱氢硅基化反应的二铑(II)配合物。该催化方法具备宽泛的底物适用范围，乙烯基芳烃底物上的给电子与吸电子取代基均可良好兼容于该反应体系。多种叔硅烷均可兼容于该脱氢硅基化反应，涵盖(EtO)3SiH、(TMSO)2MeSiH、(HSiMe2)2O、Et3SiH及Ph3SiH等。机理研究表明，在该催化体系中，四乙酸二铑(II)二聚体（Rh2(OAc)4）、DPPP与亚磷酸三甲酯（P(OMe)3）混合后可生成稳定且刚性的二铑(II)配合物，其中邻位金属化的DPPP作为桥联配体，膦酸酯作为轴向配体。该二铑(II)配合物的结构经X射线单晶衍射得以验证。进一步实验证实，该二铑(II)配合物即为催化该脱氢硅基化反应的活性物种。对照实验结果显示，降冰片烯在反应中充当氢受体，且在关键催化中间体——铑硅物种的生成过程中发挥核心作用。