Mechanistic Study on Nickel-Catalyzed Silylation of Aryl Methyl Ethers.

Abstract

The mechanism of the nickel-catalyzed silylation of aryl methyl ethers has been systematically investigated by using DFT methods. This theoretical study supports a catalytic cycle that involves the formation of a nickel-silyl complex, C-O bond cleavage, C-Si reductive elimination, the addition of methoxide to boron, and finally regeneration of the catalyst. Notably, it was found that activation of the C-O bond proceeded through an oxidative addition pathway with a three-centered transition state. The silyl anion generated in situ works as a ligand to the nickel center and promotes this process. Meanwhile, the role of the base added (KOtBu) is also elucidated. The potassium cation helps to stabilize the oxidative addition transition state through noncovalent interactions, while the resting state is destabilized due to steric repulsion introduced by the tert-butoxide anion. This is further confirmed by a comparison made computationally between the reaction with KOtBu and that with KOMe or NaOtBu as the base.