Silicon-hydrogen bond vicinal

The reaction is formally a hydrosilylation process analogous to the homogeneous reactions described in Chapter 5. Scheme 8.11 shows the proposed H—Si(lll) surface-propagated radical chain mechanism [48]. The initially formed surface silyl radical reacts with alkene to form a secondary alkyl radical that abstracts hydrogen from a vicinal Si—H bond and creates another surface silyl radical. The best candidate for the radical translocation from the carbon atom of the alkyl chain to a silicon surface is the 1,5 hydrogen shift shown in Scheme 8.11. Hydrogen abstraction from the neat alkene, in particular from the... 

The metallocene-catalyzed polymerizations of Lewis acidic monomers normally proceed well if the electronic influence of the heteroatom (B, Si, Al) is diminished by a long spacer. However, when the heteroatom locates in the vicinity of the double bond, its behavior at the metallocene cation is altered. This was clearly seen in the studies of Guram et al. [147, 148], where the vinyl-Si(CH3)3 was found to coordinate with the cationic metallocene strongly via a secondary 2,1-insertion mechanism. This was explained as being due to the electropositive nature of silicon, which drives the electron density at the internal olefinic carbon and therefore favors the 2,1-insertion (Scheme 3a) [147,148]. In contrast to vinyl-Si(CH3)3, allyl-Si(CH3)3 was found to coordinate with the metallocene catalyst via the primary 1,2-insertion mechanism [147]. The behavior of allylsilanes was rationalized on the basis of the formed polar transition state (Scheme 3b), which was stabilized by the p-effect of silicon [149]. This was also the reason for the promoted p-hydrogen abstraction after allylsUane insertions in the studies of Guram [148], Byun [150], Brandow [151], and Casey [152]. 

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