Thermal transformation of a 1,2-disilacyclobutane to a trisilacyclobutane

Thermolysis of 1,1,2,2-tetrakis(trimethylsilyl)dispiro[3,3',4,4'-biadamantane-1,2-disilacyclobutane] (6) yields (75%) the stable 1,1,2,2,3,3-hexakis(trimethylsilyl)spiro[(4,4'-adamantane)-trisilacyclobutane] (5). The structure of 5 was determined by X-ray analysis. Thermolysis of 6 probably proceeds via the simultaneous formation of two transients, bis(trimethylsilyl)adamantylidenesilene (7) and tetrakis(trimethylsilyl)disilene (11), which then undergo cycloaddition to form 5. Photolysis of 5 leads to a [2+2] cycloreversion reaction producing the silene 7 and the disilene 11. This is the first demonstration that a silene and a disilene can be generated simultaneously from a single precursor.