Radical Reactivity of Hydrovinylsilanes: Homooligomers

Diphenylvinylsilane (1) undergoes oligomerization when initiated by azobis(isobutyronitrile) or peroxide initiators (benzoyl peroxide, di-tert-butyl peroxide, dicumyl peroxide). With the exception of the reaction with di-tert-butyl peroxide, the efficiency of the radical reactions is very low: 15% starting material was recovered even with 1 equiv of added initiator. The Sivinyl groups are consumed preferentially to the SiH groups. The magnitude of the relative rates of consumption depends upon the reaction conditions and the nature of the initiator. At lower temperatures (80 °C), k Si  CH  CH2/k Si  H ≈ 2, which decreases to about 1.2 at elevated temperatures (160 °C). The relative radical reactivities of the two functional groups are discussed. The residual SiH moieties can be subsequently coupled by hydrosilation with alkynes or vinylsilicones to form star silicones.