Oxygen-silicon bonds

In ether or tetrahydrofuran organolithium reagents cleave the silicon-oxygen bond in hexamethylphosphoramide, they react at the carbon atom. ... 

Silicones are probably best known for their application as sealants and as release materials for pressure sensitive adhesives [107]. The silicone polymer combines an inorganic backbone made from silicon-oxygen bonds with organic substitution on the silicon atom. This repeating unit, shown below is called a siloxane. 

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)... 

Whether the formation of alkene 3 proceeds directly from alkoxide 4 or via a penta-coordinated silicon-species 6, is not rigorously known. In certain cases—e.g. for /3-hydroxydisilanes (R = SiMes) that were investigated by Hrudlik et al —the experimental findings suggest that formation of the carbon-carbon bond is synchronous to formation of the silicon-oxygen bond ... 

CLEAVAGE OF SILICON-CARBON AND SILICON-OXYGEN BONDS... 

Cleavage of Silicon-Carbon and Silicon-Oxygen Bonds... 

The kinetic advantages of IMDA additions can be exploited by installing temporary links (tethers) between the diene and dienophile components.132 After the addition reaction, the tether can be broken. Siloxy derivatives have been used in this way, since silicon-oxygen bonds can be readily cleaved by solvolysis or by fluoride ion.133 The silyl group can also be used to introduce a hydroxy function by oxidation. 

The complete process for synthesizing such species using this approach would entail the acquisition of an appropriate natural silicate or the preparation of an appropriate synthetic silicate and then the conversion of this silicate into the alkyl silicate or organosiloxane by suitable substitution reactions. In terms of bond cleavage, this process could entail no destruction and reformation of framework silicon-oxygen bonds, and, in terms of oxidation number, it would entail no reduction and reoxidation of the silicon. 

This process contrasts with the elemental-silicon processes sometimes used for alkyl silicates (8) and the elemental-silicon processes generally used for oligomeric and polymeric organosi-loxanes ( ,7) Since the silicon in these processes is obtained from quartz, these processes entail, in terms of bond cleavage, the destruction of four silicon-oxygen bonds per silicon and the subsequent reformation of the required number of such bonds. In terms of oxidation number, they entail the reduction of the silicon from four to zero and then its reoxidation back to four, Figures 2 and 3. 

Pauling L. (1960). The Nature of the Chemical Bond. Cornell University Press, Ithaca, N.Y. Pauling L. (1980). The nature of silicon-oxygen bonds. Amer. Mineral, 65 321-323. 

Song and co-workers have taken a variety of aldehydes 344 and treated them with A -adamantyl carbene 1 and trimethylsilyl ketene acetal 345 to produce Mukaiyama aldol products 346 in good yield (Eq. 34) [170], The carbene presumably acts as a Lewis base to activate the silicon - oxygen bond in order to promote reactivity of the enol silane. The catalyst loading can be reduced to as low as 0.05 mol% without a change in yield. 

Silicon-oxygen bond, 213 Sgl pathway, 288, 295 S vl pathway, 79, 370, 389 S 2 pathway, 78, 376 Sf/2 pathway, 110 Sfj2 aromatic) pathway, 170 Sfji pathway, %... 

It has been suggested317 that the position of ring cleavage in such cyclic, (tetraisopropyldisiloxane-l,3-diyl) derivatives on partial hydrolysis could possibly be rationalized in terms of the acidity of the carbon-bound hydroxyl group that is formed on hydrolysis of a silicon-oxygen bond. 

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