REACTIONS OF SILENES - A NEW SILENE TO SILENE THERMAL REARRANGEMENT

Photolysis of the acylsilane (Me(3)Si)TipSiCOAd at room temperature ga ve rise to two geometric isomers of (Me(3)Si)TipSi=C(OSiMe(3))Ad which are less reactive than previously reported silenes. The formation of the phenylacetylene adducts of these silenes required heating to 90 de grees C, and no reaction was observed with (trimethylsilyl)acetylene, styrene, or 2,4-hexadiene. The formation of their methanol adducts req uired heating to 100 degrees C and proved to be a stereospecific proce ss. If the original silene was heated at 120 degrees C for 5 days, in hopes of eliminating hexamethyldisiloxane and forming a silyne, a new rearranged silene (Tip)MeSi=C(SiMe(2)OSiMe(3))Ad was formed, which pro ved to be more reactive, giving adducts with phenylacetylene and metha nol. A crystal structure of the silacyclobutene formed from this rearr anged silene with phenylacetylene unequivocally confirmed its proposed structure. Heating of the rearranged silene to 150 degrees C resulted in its complete decomposition to unidentified products, and extended photolysis gave no change. The silenes (Me(3)Si)RSi=C(OSiMe(3))Ad (R = Mes, Tip) reacted with benzophenone to give 1,2-siloxetanes but did n ot react with acetone. If E-Me(3)Si(Mes)Si=C(OSiMe(3))Ad was heated to gether with styrene, a [2 + 2] cycloaddition product was formed. The c ophotolysis of (Me(3)C)(Me(3)Si)(2)SiCOAd with phenylacetylene or (tri methylsilyl)acetylene gave rise to silene cycloadducts, each a mixture of stereoisomers, suggesting that the intermediate silene also existe d as a mixture of geometric isomers.