Reactions of the Si-H bonds in tetrakis(dimethylsilyl)methane and silane

(Me2HSi)(4)M (M = C or Si) were used as: (i) branching substrates in the synthesis of hybrid single atom liquid crystal (Ic) materials (low-molecular-weight liquid crystal compounds with mesogens attached via flexible spacers to a central single atom) and (ii) free radical reducing agents for organic bromides in processes initiated by UV radiation and ultrasound (US). In the former application, hydrosilylation of the mesogenic terminal alkenes 4'-methoxy-phenyl-4-(alkenyloxy)benzoates and 4'cyano-4-(10-undecenyloxy)stilbene led to synthesis of a novel class of hybrid liquid crystals with Si or carbon as a tetrahedral centre. The respective silane and methane were found to be efficient reducing agents. For model substrates - benzyl bromide and hexadecyl bromide - all four Si-H bonds in both branched molecules are equally effective in the W-initiated reactions. The inefficiency of the ultrasound-promoted reductions is ascribed to low volatility of tetrakis(dimethylsilyl)silane and methane. (C) 2000 Elsevier Science S.A. All rights reserved.