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

Abstract

A halogen-substituted cyclic disilene compound, bromocyclotrisilene, Si 3 Br(Eind) 3 (3a), bearing fused-ring bulky Eind (a: R 1 = R 2 = Et) groups, has been synthesized as an extraordinarily air-stable compound by the reduction of 1,2dibromodisilene, (Eind)BrSi�SiBr(Eind) (2a), or tribromosilane, (Eind)SiBr 3 (1a), with the Mg or Li metal. The X-ray diffraction analysis of 3a showed that the disilene moiety has an almost planar, but slightly trans-bent structure. Even though 3a 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 3a with the Li metal leads to the formation of room-temperature thermally stable silicon homologues of the cyclopropyl radical, i.e., the cyclotrisilanyl radicals (6a) [6a(syn) and 6a(anti)], via intramolecular C−H bond activation in a transient silicon homologue of the cyclopropenyl radical, i.e., the cyclotrisilenyl radical, [Si 3 (Eind) 3 ] • (5a). The formation mechanism of 6a from 5a is discussed based on the theoretical calculations. The unique structural and electronic properties of these Si 3 three-membered ring species incorporating the Eind groups have been experimentally and theoretically investigated.