With silicon-oxygen bonds

In our environment, no family of elements is more important than Group IVb. Compounds with carbon-carbon bonds completely dominate the animal and vegetable worlds, whereas compounds with silicon-oxygen bonds almost as completely dominate that portion of the mineral world most readily accessible to man. 

The reactions of compounds with silicon-oxygen bonds continue to attract interest. A two-dimensional Si NMR study of the species present in 1.5 mol dm of potassium silicate indicates the presence of 22 different species, clear evidence of the complexity of such systems. The kinetics of the hydrolysis and self-condensa-tion reactions of (MeO)3SiMe have been studied.Iodine catalyzes the forward and back reactions in equation (21). Radicals derived from... 

As a tetravalent element, silicon can form a large number of compounds and structures with itself and with other elements. Only those with silicon-oxygen bonds, however, have become significant as macromolecular substances, that is, silicates and silicones. 

T resonances in the 29gi NMR spectra arise from silicon species with one substituent attached through a carbon-silicon bond and three substituents attached with silicon-oxygen bonds RSi(OH)3 = T , [RSiOi.5] n=... 

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)... 

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. 

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. 

Another modification of the double silylation process reported by Tanaka and co-workers involves the use of a bis(hydrosilane) instead of a disilane as the reactant molecule.61 This reaction can be described as a dehydrogenative double silylation, in that two Si-H bonds are activated rather than an Si-Si bond. The system is best catalyzed by Pt(CH2=CH2)(PPh3)2 other Pt, Pd, Ru, and Rh complexes give only very low yields of the double-silylated products. Alkynes, alkenes, and dienes undergo reaction with the bis (hydrosilane) with a range of results. Silicon-oxygen bonds and silicon-nitrogen bonds can also be formed by this method and are discussed in the appropriate sections later. 

In 1952, Khaskin [14] showed that under acidic conditions. Equation (1) occurs with breakage of the silicon oxygen bond. This was proven using, kO labeled water. The reaction proceeded with the inclusion of the, kO in the resulting silanol as follows ... 

Acyl silanes often, however, exhibit abnormal behaviour, for example involving rearrangements leading to silicon-oxygen bond formation, especially when treated with... 

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