The synthesis and characterization of a series of fluorinated benzosiloxaboroles bearing synthetically useful formyl and cyano groups is reported. These compounds have been obtained by multistep syntheses starting with simple halogenated benzenes. The general synthetic protocol was based on the generation of ortho‐boronated aryldimethylsilanes which undergo dehydrogenative cyclization upon hydrolytic workup due to activation of the Si–H bond by the adjacent boronic group. In some cases the synergy of adjacent boron‐ and silicon‐based functionalities resulted in an unexpected hydrosilylation of the CHO group under mild aqueous conditions. The reduction of a benzosiloxaborole derivative bearing the formyl group at the ortho position with respect to the boron atom resulted in a structural transformation reflecting the higher stability of the carboxaborole heterocycle with respect to its silicon counterpart. Thus, a unique heterocyclic system featuring a central 10‐membered ring comprising two borasiloxane linkages was isolated.

An intramolecular activation of the Si-H bond in arylsilanes by selected ortho-assisting functional groups based on boron, carbon and phosphorus was investigated experimentally and by means of theoretical calculations. The major conclusion drawn is that the presence of a negatively charged oxygen atom in the functional group is essential for providing effective chelation to the silicon atom which in turn results in the increased hydridic character of a resulting five-coordinated species. In contrast, an intermolecular attack of hydroxide on the silicon atom in aryldimethylsilane results in the activation of the silicon-aryl bond. This increased reactivity of the Si-H bond in intramolecularly coordinated arylsilanes can be ascribed to a significant trans effect which operates in the preferred configuration. Hydrolytic cleavage of the Si-H bond results in dihydrogen elimination and the formation of various silicon heterocyclic systems such as benzosiloxaboroles, spiro-bis(siloxa)borinate, benzosilalactone and benzophosphoxasilole. In addition, intermolecular reduction of benzaldehydes with ortho-boronated arylsilane was observed whereas compounds bearing other reducible functional groups (COMe, COOEt, CN and NO) were inert under comparable conditions. Specifically, an intramolecular reduction of the CN group in an ortho-silylated benzonitrile derivative was observed. The mechanism of Si-H bond activation was investigated by the DFT theoretical calculations. The calculations showed that the intramolecular coordination of the silicon atom effectively prevents the cleavage of the Si-aryl bond. Furthermore, the reaction is favored in anionic systems bearing COO, B(OH) or CHO groups, while in the case of neutral functional groups such as PO(OEt) the process is much slower.