Reactions of a cyclotrisilane with styrene derivatives and diarylacetylenes - evidence for nucleophilic silylenes

Silaindanes were obtained by reaction of hexakis[2-(dimethylaminomethyl)phe nyl]cyclotrisilane (3) with 3 equiv. of various styrenes. Analogous treatme nt of 3 with p-methoxystryrene yielded a mixture of the corresponding silai ndane and a 2:1 adduct between bis[2-(dimethylaminomethyl)phenyl]silylene ( 4) and the styrene. Competition experiments show that the addition rate of 4 to the triple bond of diarylacetylenes is accelerated by electron-withdra wing substituents. The reaction constant (p=+0.85+/-0.21) indicates that 4 acts as a nucleophile in these reactions. The rate determining step in thes e reactions of cyclotrisilane 3 is the formation of silylene 4. The rate co nstant for this first order process was determined to be (6.3+/-0.4)x10(-4) s(-1) at 60 degreesC. (C) 2001 Elsevier Science Ltd. All rights reserved.