Modular construction of neutral and anionic carboranyl-containing carbosilane-based dendrimers

A modular construction of new carbosilane dendrimers, which contain four and eight peripheral carborane derivatives and propyl linkages between the C-cluster and the Si atoms, has been developed using different methodologies. Regiospecific hydrosilylation of 1-C6H5-2-(CH2CHCH2)-l,2-closo-C2B10H10 (1) and 1-CH3-2-(CH2CHCH2)-1,2-closo-C2B10H10 (2) offers an efficient route to molecular precursors and building blocks that can provide both divergent and convergent strategies for dendritic growth. First generations of neutral carboranyl-containing dendrimers were constructed by two approaches: (a) a divergent approach via hydrosilylation of 1 and 2 with the first generation of a carbosilane dendrimer containing peripheral Si-H functions, Si[(CH2)(2)(CH3)(2)SiH](4), 1G-H-4, to give dendrimers 7 and 8, respectively; (b) a convergent strategy, the growth of which was initiated with the groups that will become the periphery of the dendrimer. In the latter, the hydrosilylation of the allyl group in 1 and 2 with Me2HSiCl was carried out leading to the formation of 1-(CH2)(3)SiCl-2-R-1,2-closo-C2B10H10 [R = C6H5 (3), CH3 (4)], and subsequent reduction with LiAlH4 gave compounds 1-(CH2)(3)SiH-2-R-1,2-closo-C2B10H10 [R = C6H5 (5), CH3 (6)], which were treated with tetravinylsilane or the core molecule to yield the first generation dendrimers, 7 and 8, with four carborane clusters. Next generation dendrimers were built up in a similar manner: (a) by the hydrosilylation using 1G-H-4 of the vinyl group in dendrons 9 and 10, which themselves have been prepared from the alkenylation of 3 and 4 with vinylmagnesium chloride; (b) by growing the carboranylsilane wedges 9 and 10 to a second generation and later assembling all to the core tetravinylsilane to obtain dendrimers 15 and 16. In addition, another set of a second generation dendrimers containing eight carborane clusters were prepared by hydrosilylation of the vinyl groups in the dendrimer Si{(CH2)(2)(CH3)Si[(CHCH2)(2)]}(4), 1G-Vi(8), with carboranylsilane dendrons 5 and 6, that contain Si-H functions. Degradation reaction of the peripheral closo-carboranes in dendrimers 7 and 8 using KOH/EtOH led to the formation of the corresponding polyanionic carbosilane dendrimers containing four peripheral nido-carborane clusters.