Dehydrogenative silation

The main side reaction of the hydrosilation reaction is the dehydrogenating silation reaction. Under certain conditions this reaction can be the main or even the exclnsive reaction. The reaction can occnr, not only with alkenes, bnt also with almost all known substrates. It achieves vinylsilanes from alkenes, silylalkynes from alkynes, and silyl enol ethers from ketones. ... 

Besides the reversible processes just mentioned, yS-SiRs ehmination from a silyl substituted metal alkyl or metallacycle is a well-documented process [185,186]. This reaction accounts for an easy loss of a silyl group that can be used to generate a M-S1R3 moiety in catalytic processes such as dehydrogenative silation reactions (see below). This reaction, and the analogous yS-SnRs elimination, may also be involved in the loss of regioselectivity found for some C-C coupling reactions of vinyl silanes or vinyl tin derivatives (cine substitution in Hiyama and Stille... 

Several synthetically very useful processes involve the 1,2 insertion of unsaturated substrates into the M-SiRs bond (hydrosilation [193], dehydrogenative silation [193a,194], and disilation [176]) or the M-BR2 bond (hydroboration [195], dehydrogenative boration [196], and diboration [191,195,197]) Catalytic reactions have been developed lately that comprise the 1,2 addition of two different ER groups to an alkene or alkyne (silylstannation [198], borylsilation... 

The hydrosilation and hydroboration of alkenes produce a saturated tetraalkyl silicon or boron derivative (Eq. 6.33). In addition dehydrogenative silation or boration derivatives are sometimes encountered as side products. These are substituted alkenes analogous to the Heck reaction products where a new C-Si (or C-B) bond is formed instead of a C-C bond (Eq. 6.34). 

Systems and conditions that proceed cleanly by route c (Scheme 6.62) are efficient for catalytic dehydrogenative silation. A M-SiRs source is necessary and this can be a silane, with concomitant reduction of the alkene to give an alkane (Scheme 6.62, c). /l-SiRa elimination has been artfully used to produce a M-SiRs moiety from vinylsilanes or allylsilanes. Scheme 6.63 depicts the use of allylsilanes described by Murai et ai. to produce silyl substituted alkenes and propene as byproduct [194b]. 

LaPointe AM, Rix FC, Brookhart M (1997) Mechanistic studies of palladium(ll)-catalyzed hydrosilation and dehydrogenative silation reactions. J Am Chem Soc 119 906-917... 

Although their work does not strictly fall within the scope of this review, Hartwig and Tsukuda s report on dehydrogenative silation via arene-H and alkane-H... 

Sadow AD, Tilley TD (2005) Synthesis and charactraizahon of scandium silyl complexes of the type Cp 2ScSiHRR. o-hond metathesis reactions and catalytic dehydrogenative silation of hydrocarbons. J Am Chtan Soc 127 643... 

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