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, 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 1,2-dibromodisilene, (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.