Metathesis of vinylsilanes

The cross metathesis of vinylsilanes is catalyzed by the first-generation ruthenium catalyst 9. This transformation has been extensively investigated from both preparative and mechanistic points of view by Marciniec et al. [86]. Interestingly, the same vinylsilanes obtained from cross metathesis may also result from a ruthenium-hydride-catalyzed silylative coupling and there might be some interference of metathesis and nonmetathesis mechanisms [87]. 

Evidence for the migratory insertion of ethylene [46] and vinylsilane [47] into the Ru-Si bond yielding vinylsilane and two bis(silyl)ethene regioisomers [E-l,2-bis(silyl)ethene and l,l-bis(silyl)ethene],respectively,has proved that in the reaction referred to as the metathesis of vinylsilanes and their cometathesis with olefins, instead of the C=C bond cleavage formally characterizing alkene metathesis (Eq. 24a), a new type of olefin conversion that is a silylative coupling of olefins with vinylsilanes occurs (Eq. 24b). 

The reaction of vinyl-substituted silanes and octavinylsilsesquioxane with vinyl-substituted amides, amines (carbazole) as welt as boronates catalyzed by I proceeds effectively to yield under optimum conditions stereo- and/or regio-selectively l-silyl-2-/V- and 1,1-silylboryl-substituted ethenes. 1-silylvinyl carbazole can also be obtained via cross-metathesis of vinylsilane with vinylcarbazole, but only in the presence of the 2nd generation Grubbs catalyst (IV). 

Cross-metathesis of Vinylsilanes with Alkenes Catalyzed by Ruthenium-carbene Complexes... 

Highly selective cross-metathesis of vinylsilanes and vinylsiloxanes with styrene occurs under very mild conditions even at room temperature. This provided evidence for a metallacarbene mechanism catalyzed by RuCl2(PCy3)2Ru=CHPh. The reaction proceeds as in equation 18. 

In this contribution, we will overview reactivity modes and efficient synthetic routes based on metathesis transformations of vinylsilanes in the presence of Grubbs catalysts. The efficient cross-metathesis of vinylsilanes, carrying a large spectrum of different substituents at silicon, with various olefins in the presence of the first- and second-generation Grubbs catalyst and Hoveyda-Grubbs catalyst is described (Eq. 1). 

The effect of substituents at silicon on the reaction is outlined. We discuss advantages and drawbacks of cross-metathesis of vinylsilanes with olefins as a general method for the synthesis of vinyl-trisubstituted silanes and finally present a general mechanistic scheme that explains the processes taking place in the studied systems. Moreover, recent results on the cross-metathesis of a variety of (di)vinyl-substituted silanes, disiloxanes, and monovinyl-substituted siloxanes with olefins are reported [5]. 

The efficient and stereoselective cross-metathesis of vinylsilanes canying electron-withdraAving substituents with various olefins has likewise been described (Eq. 9) [15]. 

The reactivity of vinylsiloxanes provided important clues concerning the functionalization and cross-linking of poly(vinyl)siloxanes. Preliminary investigations showed a limited reactivity of poly(vilyl)siloxanes in the functionalization via cross-metathesis [21]. A pronounced influence of the properties of the substituents at silicon on the metathesis of vinylsilanes was observed (Eq. 18) [21]. 

Class 2 eonsists of vinylsilanes that exhibit activity both in Aowo-metathesis and cross-metathesis with olefins. Only one substituent motif , that is H2C=CHSiCl2R (where R = alkyl, aryl, OSiMes) was found to be eharaeteristie of this elass. Cross-metathesis of H2C=CHSiCl2R with olefins eatalysed by n or IH gives cross-metathesis products with high yields and selectivities. For these silanes, care must be taken to choose the proper reaetion eonditions as well as the vinylsilane to olefin ratio because crossmetathesis is aeeompanied by competitive homo-metathesis of vinylsilane and olefin. 

Olefin metathesis has been established as a standard tool in organic synthesis, and is also applicable to the synthesis of organosilicon reagents. For example, crossmetathesis of allylsilanes provides an efficient access to more substituted and functionalized allylsilanes (Scheme 3-64). ° The cross-metathesis of vinylsilanes is a convenient method to prepare substituted vinylsilanes.For example, the reaction of... 

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