Synthesis of B/Si Bidentate Lewis Acids, o-(Fluorosilyl)(dimesitylboryl)benzenes, and Their Fluoride Ion Affinity

o-(Fluorosilyl)(dimesitylboryl)benzenes have been prepared as colorless crystals by reacting fluorodimesitylborane with o-(fluorodimethylsilyl)phenyllithium and o-(fluorodiphenylsilyl)phenyllithium. The o-(fluorosilyl)(dimesitylboryl)benzenes serve as B/Si bidentate Lewis acid and efficiently capture fluoride ion from potassium fluoride in the presence of [2.2.2]cryptand or 18-crown-6 in toluene, giving the corresponding mu-fluoro bridged products. The structures were characterized by X-ray crystal structure analysis and multinuclear NMR spectroscopy. Fluoride ion affinities of the o-(fluorosilyl)(dimesitylboryl)benzenes were evaluated in comparison with non-silylated triarylborane.