C─H Silylation of Unactivated Arenes Catalyzed by a Borenium/Pyridine Lewis Pair.

Non-noble-metal-catalyzed C─H silylation of arenes provides a straightforward and sustainable method for the functionalization of arenes. However, to date, it has been limited to electron-rich arenes. Here we report a Lewis pair, composed of a highly Lewis acidic borenium ion and a weak pyridine base, can catalyze C─H silylation of benzene and other unactivated arenes with H2SiArF 2 (ArF = 2,4,6-trifluorophenyl) as silylation reagent under neat conditions. Unlike most of its noble metal counterparts, this metal-free system does not require stoichiometric sacrificial hydrogen acceptors. Additionally, this system can be applied for direct C─H silylation of polystyrene, opening a new avenue for the functionalization of polystyrene. Our mechanistic investigations revealed that the activation of H2SiArF 2 by the Lewis pair leads to the formation of a pyridine-coordinated silylium intermediate, which was isolated and characterized by X-ray diffraction analysis. Kinetic isotope effect (KIE) studies and theoretical calculations suggest that the C─H activation mediated by this silylium intermediate is likely the rate-limiting step.