Direct Formation and Reactivity of a Bromo- and Amido-Substituted Cyclotrisilene

The reaction of {N­(tBu)­Trip}­SiBr3 (1, Trip = 2,4,6-iPr3C6H2) with 1.5 equiv of activated magnesium
(Mg*) directly
provides the amido-substituted cyclotrisilene 2 with
one bromine substituent in 29% yield. In 2, negative
hyperconjugation from the SiSi π-bond into antibonding
σ*-orbitals of the Si1–N1 and Si1–Br1 bonds occurs.
This results in remarkably more shielded silicon atoms of the SiSi
bond compared to aryl- and silyl-substituted cyclotrisilenes. The
reaction with the N-heterocyclic carbene NHCMe4 does not
result in ring-opening but instead yields the NHC adduct 3. Nevertheless, cyclotrisilene 2 reacts with ethylene
and dimethylacetylene in [2 + 2] cycloadditions to result in bicyclic
saturated and unsaturated housanes 4 and 5, respectively.