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 C-cluster-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 (1G(A)-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-C2B(10)H(10) (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.