Syntheses and reactivity of stannyloligosilanes. 2. Branched stannyloligosilanes

Branched tri(stannyl)tetrasilanes MeSi[SiMe2SnR2R'](3) (2, R = R' = Ph; 3, R = R' = Me; 5, R = t-Bu, R' = H) were synthesized by the reaction of alkal i metal tri- or diorganostannides with methyltris(fluorodimethylsilyl)silan e (1) or methyltris(chlorodimethylsilyl)silane (4) or by reacting triphenyl chlorostannane with 1 in the presence of magnesium. Methyltris[(hydridodi-t ert-butylstannyl)dimethylsiyl]silane (5) was halogenated at the tin atom by treatment with CHCl3 or CHBr3. Surprisingly, the reaction of 5 with 3 equi v of lithium diisopropylamide (LDA) resulted in the formation of the five-m embered ring 10 (2-dimethylsilyl-1,1,2,3,3-pentamethyl-4,4,5,5-tetra-tert-b utyl-1,2,3-trisila-4,5-distannacyclopentane) with a bridging Sn-Sn unit. Re acting 5 with triethylamine or aminostannanes resulted in the formation of 2-dimethylsilyl-1,2,3,3-pentamethyl-4,4,5,6,6-penta-tert-butyl-1,2,3-trisil a-4,5,6-tristannacyclohexane (14). The solid-state structures of 5 and 14b were determined by X-ray crystallography.