Me ₃ SiBr/InCl ₃ catalyzed allylation of alcohols: Identifying the combined Lewis structure and investigating the reaction mechanism

The combined Lewis acid Me ₃ SiBr/InCl ₃ shows unique performance in multireactions. The topology and catalytic properties of Me ₃ SiBr/InCl ₃ were investigated by DFT method for clarifying the nature of chemical bonds and interactions. Quantum theory of atoms in molecules (QTAIM) analysis showed that the interaction between Me ₃ Si-halide and In-trihalide mainly belongs to the closed-shell interaction. Natural bond order of Br─In is 0.610 in INT_0 while natural bond order of Cl─In in INT_1 is only 0.081 at SMD-ωB97XD/def2-SVP level. The coupling reaction mechanism of alcohol and allyltrimethylsilane catalyzed by the complex of Me ₃ SiBr/InCl ₃ was investigated with DFT method. The combined Lewis acid activates the hydroxyl group by strong coordination to silicone center, which leads to the generation of carbocation. Me ₃ Si ⁺ moiety from the combined Lewis acid is consumed and converts into the side product Me ₃ SiOSiMe ₃ . Furthermore, the reactant allyltrimethylsilane is introduced into the system to bring out the final product, and the complex Me ₃ SiBr/InCl ₃ is reproduced at the same time. The combined Lewis acid Me ₃ SiBr/InCl ₃ not only works as the catalyst for the reaction but also involves in the generation of side product.