Alkoxysilanes cleavage

Important evidence in support of this mechanism was provided by carrying out hydrolysis with oxygen-isotope-labeled water (H2 0). The isotope test showed that the alkoxysilane cleavage is carried out by breaking the Si-OC bond rather than by cleavage of the SiO-C bond, resulting in the formation of the heavy silanol =Si OH and not the light =Si OH. 

Alkyl silyl ethers are cleaved by a variety of reagents Whether the silicon-oxygen or the carbon-oxygen bond is cleaved depends on the nature of the reagent used Treatment of alkoxysilanes with electrophilic reagents like antimony tri-fluonde, 40% hydrofluonc acid, or a boron tnfluonde-ether complex results in the cleavage of the silicon-oxygen bond to form mono-, di-, and tnfluorosiloxanes or silanes [19, 20, 21) (equations 18-20)... 

The hydrolytic cleavage of the Si—N bond of aminosilanes does not proceed so fast as compared to the Si—0 and Si—Cl bond in similar alkoxysilanes and chloro-silanes, respectively. However, the hydrolysis can be accelerated by acidic catalysts. 

Alternatively if an alkoxysilane is used, a second oxidation method is applicable. Thus epoxidatitm of the vinylsilane (100) and oxidative cleavage of the crude silyl epoxide (101) provides a go yield of the product (102). The conversion (101) to (102) involves peroxidation of Ae silylalkoxy group and con-... 

Within the scope of systematic investigations on basic reactions in industrial silicone syntheses in the system - alkoxysilane, silanol, siloxane, alcohol, water, catalyst, solvent - after previous investigations on the equilibrium of the silanol alkoxysilane heterocondensation and the reverse siloxane cleavage with alcohol (Eq. 1) [1]... 

A proposed mechanism for the rhodium-catalyzed alcoholysis is represented in Scheme 49 (77). In the first step, activation of the hydrosilane occurs through oxidative addition. Formation of the alkoxysilane then takes place by nucleophilic attack of a noncoordinated alcohol molecule. The dihydro-rhodium complex 143 thus obtained liberates a hydrogen molecule upon reductive elimination. Nucleophilic cleavage of the silicon-rhodium bond, without prior coordination of the alcohol at the rhodium is supported by results obtained in asymmetric alcoholysis (cf. Sect. II-D). Optical yields were shown to be little dependent on the catalyst ligands (in marked contrast with the asymmetric hydro-silylation), indicating but weak interaction between alcohol and catalyst during the reaction. Moreover, inversion of configuration at silicon, which occurs in the particular case of methanol as solvent, is not likely to occur in a reaction between coordinated silane and alcohol. 

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