Silicon Analogues of Cyclopropyl Radical Derived from a Highly Stable Cyclic Disilene Compound Featuring a Si-Br Bond.

A halogen-substituted cyclic disilene compound, bromocyclotrisilene, SiBr(Eind) (), bearing fused-ring bulky Eind (: R = R = Et) groups, has been synthesized as an extraordinarily air-stable compound by the reduction of 1,2-dibromodisilene, (Eind)BrSi═SiBr(Eind) (), or tribromosilane, (Eind)SiBr (), with the Mg or Li metal. The X-ray diffraction analysis of showed that the disilene moiety has an almost planar, but slightly -bent structure. Even though is quite air-stable both in solutions and in the solid state, its Si-Br bond is reactive under reducing conditions. The further treatment of with the Li metal leads to the formation of room-temperature thermally stable silicon homologues of the cyclopropyl radical, i.e., the cyclotrisilanyl radicals () [() and ()], via intramolecular C-H bond activation in a transient silicon homologue of the cyclopropenyl radical, i.e., the cyclotrisilenyl radical, [Si(Eind)] (). The formation mechanism of from is discussed based on the theoretical calculations. The unique structural and electronic properties of these Si three-membered ring species incorporating the Eind groups have been experimentally and theoretically investigated.