Trapping Experiments during Reductive Debrominations of Aminotribromosilanes with Alkenes

Keuter J., Hepp A., Lips F.

Abstract

In-situ generated amido-substituted disilynes (SiMe3)2N−Si≡Si−N(SiMe3)2 1 and (SiMe3)DippN−Si≡Si−N(SiMe3)Dipp 2 were observed examined upon the reductive dehalogenation of the tribromosilanes {N(SiMe3)2}SiBr3 3 and {N(SiMe3)Dipp}SiBr3 4 with Rieke magnesium (Mg*). Both disilynes were trapped with ethylene to yield the double [2+1] and [2+2] cycloaddition products 5 and 6, respectively. The transient disilynes 1 and 2 were investigated with DFT calculations that revealed 1 to feature more triple bond character than 2. The in-situ generated disilyne 2 was further quenched with 1,5-cyclooctadiene to yield the double [2+2] cycloaddition product 7. In the presence of cyclooctatetraene, the reductive debromination of 4 with Mg* generates the bromo-substituted silacyclopentene 8. This species was also isolated with 2,3-dimethyl-1,3-butadiene used as trapping reagent as the major product 9, besides the side product 10, that comprises two cyclotrisilene rings linked via a butene unit. The formation of 10 shows that a cyclotrisilene can occur as a side product during the reductive debromination of 4 in the presence of the alkene.