Reprinted from J. Am. Chem. Soc., 120, 1398-1404 (1998).

1998, American Chemical Society

Thermal and Photochemical [2+2] Cycloreversion of a 1,2-Disilacyclobutane and a 1,2-Digermacyclobutane

Y. Apeloig,* D. Bravo-Zhivotovskii, I. Zharov, V. Panov, W. J. Leigh,* and G. W. Sluggett

Contribution from the

Department of Chemistry & the Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa 32 000, Israel

and the

Department of Chemistry, McMaster University, Hamilton, Ontario, Canada L8S 4M1

Abstract: Upon heating of the highly sterically congested 1,1,2,2-tetrakis(trimethylsilyl)dispiro[3,3',4,4'-biadamantane-1,2-disilacyclobutane] (2) in solution in the presence of trapping reagents such as 1,3-butadienes, styrene, phenylacetylene and methanol, the trapping products of the silene bis(trimethylsilyl)-adamantylidenesilane (1) are formed with high regioselectivity and good yields. Photolysis of 2 at -196oC in methylcyclohexane in the absence of trapping agents produces tetrakis(trimethylsily)disilene (3). Photolysis of 2 in solution in the presence of 1,3-butadiene leads to 2,2'-biadamantylidene and a 2:1 mixture of 1,1,2,2-tetrakis(trimethylsilyl)-1,2-disilacyclohex-4-ene (10) - the trapping product of the disilene 3 - and 1,1-bis(trimethylsilyl)-1-silacyclopent-3-ene (11) - the trapping product of bis(trimethylsilyl)silylene (4). The results of laser flash photolysis and of additional trapping experiments suggest that the sole primary product in the photolysis of 2 is the disilene 3, which dissociates under further irradiation to produce the silylene 4. Heating of 1,1,2,2-tetrakis(trimethylsilyl)dispiro[3,3',4,4'-biadamantane-1,2-digermacyclobutane] (14) in solution results in the quantitative formation of 2,2'-biadamantylidene and of germanium-containing oligomers, while neither bis(trimethylsilyl)adamantylidenegermene (15) nor tetrakis(trimethylsilyl)digermene (16) or bis(trimethylsilyl)germylene (17) could be trapped. Upon photolysis, 14 behaves similarly to 2, leading to 16 and 17 which could be trapped by 1,3-butadiene.