THERMAL AND PHOTOCHEMICAL [2-DISILACYCLOBUTANE AND A 1,2-DIGERMACYCLOBUTANE(2]CYCLOREVERSION OF A 1,2)

Upon heating of the highly sterically congested piro[3,3',4,4'-biadama ntane-1,2-disilacyclobutane] (2) in solution in the presence of trappi ng reagents, such as 1,3-butadienes, styrene, phenylacetylene, and met hanol, the trapping products of the silene bis(trimethylsilyl)adamanty lidenesilene (1) are formed with high regioselectivity and good yields . Photolysis of 2 at -196 degrees C in methylcyclohexane in the absenc e of trapping agents produces tetrakis(trimethylsilyl)disilene (3). Ph otolysis of 2 in solution in the presence of 1,3-butadiene leads to a 2:1 mixture of -tetrakis(trimethylsilyl)-1,2-disilacyclohex-4-ene (10) -the trapping product of the disilene 3-and of 1,1-bis(trimethylsilyl) -1-silocyclopent-3-ene (11)-the trapping product of bis(trimethylsilyl )silylene (4)-together with 2,2'-biadamantylidene. The results of lase r flash photolysis and of additional trapping experiments suggest that the sole primary product in the photolysis of 2 is the disilene 3, wh ich dissociates under further irradiation to produce the silylene 4. H eating of iro[3,3',4,4'-biadamantane-1,2-digermacyclobutane] (14) in s olution results in the quantitative formation of 2,2'-biadamantylidene and of germanium-containing oligomers, while neither bis(trimethylsil yl)adamantylidenegermene (15) nor tetrakis(trimethylsilyl)digermene (1 6) or bis(trimethylsilyl)germylene (17) could be trapped. Upon photoly sis 14 behaves similarly to 2, leading to 16 and 17, which could be tr apped by 1,3-butadiene.