Rare-Earth-Catalyzed Regiodivergent Hydrosilylation of Aryl Alkenes

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*(AmScCH2SiMe3)-Sc-tBu (Cp* = pentamethylcyclopentadienyl, Am-tBu = (BuNC)-Bu-t(Me) N-tBu, Bu-t = 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*(AmNdCl)-Nd-iPr](2) (Am-iPr = (PrNC)-Pr-i(Me)(NPr)-P-i, P-i(r) = 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.