Disilabicyclo octadiene, disilenes

Photolytic [4+2] cycloreversion of a disilabicyclo[2.2.2]octadiene precursor is considered to be a general method for the synthesis of disilenes of varying stability. Several examples of this method have been reported (Eq. 9).27-31 First used in reactions producing an unstable disilene, Me2 Si=SiMe2,27 this method is also successful for synthesizing the marginally stable -Bu2Si=Si(t-Bu)2,28 However, it has not yet been applied to the synthesis of disilenes that are fully stable at room temperature, probably because the appropriate precursors are inaccessible. 

Generation of various phenyl-substituted disilenes by the photolysis of the masked disilenes, 7,8-disilabicyclo[2.2.2]octadiene derivatives, is quite useful, especially for unsymmetrically substituted disilenes. Investigation of the regiochemistry as well as the diastereochemistry of alcohol addition to phenyltrimethyldisilene was made possible for the first time by using this method27. 

Tetraisopropyldisilene was obtained from the disilabicyclo[2.2.2]octadiene 4 by photochemical 4 + 2 cycloreversion, as judged by the formation of its methanol adduct in a trapping experiment48. When 4 was irradiated in the absence of a trapping agent, octaisopropylcyclotetrasilane was isolated along with some reduction product, 1,1,2,2-tetraisopropyldisilane (equation 5). It is quite possible, but not certain, that both of these are formed in reactions of an electronically excited disilene. 

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