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

Abstract

The reaction of {N(tBu)Trip}SiBr 3 (1, Trip = 2,4,6-iPr 3 C 6 H 2 ) 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 NHC Me4 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.

Synthesis and Reactivity of Aluminum Disilacyclopropenes. Cyclic AlSi2 Delocalized 2π Systems

“…Reactions of a tricyclosilene with styrene and ethylene have been reported to go through [2 + 2] cycloaddition with the endocyclic SSi double, leading to the formation of silicon–carbon mixed housanes. , However, further insertion of the alkenes to the bicyclic housanes was not observed. The full insertion of four molecules of ethylene into all of the AlSi 2 cyclic bonds in 4b indicates synergistic activity of the Al–Si and Si–Si bonds.…”

“…In the late 1990s, Sekiguchi and Power independently reported the first synthesis of cyclotrigermenes and a cyclotrigermene radical . Following the seminal work, an explosive growth of heavy group 14 cyclopropenes has been witnessed. − Furthermore, some related heavy group 13 three-membered rings have also been reported. − However, unsaturated three-membered rings composed of elements from both groups 13 and 14 are very limited. − Because of the electron deficiency of three-coordinate group 13 ions, these heteronuclear 2π-electron systems are isoelectronic with cyclopropenium cations . Although BC 2 unsaturated rings (borirenes) have been well-documented, the heavy heteronuclear systems are much less common.…”