Trapping Experiments during Reductive Debrominations of Aminotribromosilanes with Alkenes

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.