Rare-Earth-Catalyzed Regiodivergent Hydrosilylation of Aryl Alkenes

Wufeng Chen^#, Ni Zhang^#, Zhengqi Chai, Junnian Wei, Gen Luo* and Wen-Xiong Zhang*

ACS Catal. 2024, 14, 5612-5620. ( ^#Authors contributed equally) 

https://doi.org/10.1021/acscatal.3c05747

　　While transition metal-catalysts have shown the ability to regulate the Markovnikov or anti-Markovnikov regioselective hydrosilylation of aryl alkenes, the selective control of anti-Markovnikov hydrosilylation of aryl alkenes is still a huge challenge in rare-earth catalyst systems. In this study, we report the rare-earth-catalyzed regiodivergent hydrosilylation of aryl alkenes. Specifically, we achieved the highly regioselective anti-Markovnikov hydrosilylation of aryl alkenes with a scandium alkyl complex Cp*Am^tBuScCH₂SiMe₃ (Cp* = pentamethylcyclopentadienyl, Am^tBu = ^tBuNC(Me)N^tBu, ^tBu = t-butyl) as a catalyst. Two key intermediates, e.g. the scandium hydride and scandium phenethyl complex for anti-Markovnikov hydrosilylation, were characterized. Guided by Density Functional Theory (DFT) calculations, we successfully achieved the selective inversion of aryl alkenes in Markovnikov hydrosilylation using a neodymium halide complex [Cp*Am^iPrNdCl]₂ (Am^iPr = ⁱPrNC(Me)NⁱPr, ⁱPr = isopropyl) with the larger ion radius and reduced steric hindrance in conjunction with LiCH₂SiMe₃. Interestingly, our study has demonstrated the significant influence of gradually increasing rare-earth ion radii on controlling the increasing Markovnikov selectivity of hydrosilylation reactions, possibly due to the enlargement of the coordination space around rare-earth metal ions. Furthermore, through a comparison of computational and experimental data, we have observed a high level of consistency, reaffirming the potential of using calculations to predict experimental outcomes and providing researchers with valuable insights.