Hydrodefluorination and Other Hydrodehalogenation of Aliphatic Carbon-Halogen Bonds Using Silylium Catalysis

摘要

Trialkylsilylium cation equivalents partnered with halogenated carborane anions (such as Et_3Si[HCB_(11)H_5Cl_6]) function as efficient and long-lived catalysts for hydrodehalogenation of C-F, C-CI, and C-Br bonds with trialkylsilanes as stoichiometric reagents. Only C(sp~3)-halogen bonds undergo this reaction. The range of C-F bond-containing substrates that participate in this reaction is quite broad and includes simple alkyl fluorides, benzotrifluorides, and compounds with perfluoroalkyl groups attached to an aliphatic chain. However, CF_4 has proven immune to this reaction. Hydrodechlorination was carried out with a series of alkyl chlorides and benzotrichlorides, and hydrodebromination was studied only with primary alkyl bromide substrates. Competitive experiments established a pronounced kinetic preference of the catalytic system for activation of a carbon-halogen bond of a lighter halide in primary alkyl halides. On the contrary, hydrodechlorination of C_6F_5CCI_3 proceeded much faster than hydrodefluorination of C_6F_5CF_3 in one-pot experiments. A solid-state structure of Et_3Si[HCB_(11)H_5CI_6] was determined by X-ray diffraction methods.