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

Silaindanes were obtained by reaction of hexakis[2-(dimethylaminomethyl)phenyl]cyclotrisilane (3) with 3 equiv. of various styrenes. Analogous treatment of 3 with p-methoxystryrene yielded a mixture of the corresponding silaindane 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-withdrawing substituents. The reaction constant (ρ=+0.85±0.21) indicates that 4 acts as a nucleophile in these reactions. The rate determining step in these reactions of cyclotrisilane 3 is the formation of silylene 4. The rate constant for this first order process was determined to be (6.3±0.4)×10−4 s−1 at 60°C.