Boron-Functionalized Carbosilanes: Insertion of Carborane Clusters into Peripheral Silicon Atoms of Carbosilane Compounds

Two families of carborane-containing star-shaped carbosilane molecules have been
synthesized. Three different carborane cages 1-R-1,2-C2B10H11, in which the R group possesses
different bulkiness (R = H, Me, Ph), have been introduced on the carbosilane periphery
through Ccluster−Si bonds. The first family, 1−3, is derived from a chlorosilane that contains
two carbon atoms as the branch point (1GV-Cl), whereas in the second one, 4−6, the branch
length has been changed (1GA-Cl) in order to study the size and flexibility of the compound
in both the reaction with carboranes and the final products. Two different methods have
been used for their preparation:  (a) the nucleophilic substitution of the periphery Si−Cl
functions with the corresponding carborane monolithium salt; (b) the hydrosilylation reaction
of tetravinyl or tetraallylsilane with the carboranylsilanes 1-Me2HSi-2-Me-1,2-C2B10H10 (7)
and 1-Me2HSi-2-Ph-1,2-C2B10H10 (8) catalyzed by Karsted's catalyst. The first method leads
to compounds that incorporate four carboranyl moieties covalently bonded to the peripheral
Si atoms of a carbosilane core; nevertheless, differences in the final product yields are
observed depending on the carborane derivatives and the starting chlorosilane. The
hydrosilylation reaction was a highly efficient method to obtain 2 and 3 in large yield;
nevertheless, this process was not successful to prepare 5 and 6. In addition, it is important
to emphasize that 1−3 were successfully isolated in crystalline form suitable for X-ray
diffraction analyses. Furthermore, the X-ray crystal structure of the carboranylsilane 1-Me2HSi-2-Ph-1,2-C2B10H10 (8) is also reported.