Halogen silicon—oxygen bonds

The silicon-halogen, silicon-oxygen, and silicon-sulfur bonds of the haiogenosil-anes, siiyl ethers, and siiyi thioethers are cleaved by reaction with LAH, AIH3, or DIBAH, and the corresponding siiyl hydrides are obtained [CGI, CG2]. Ultrasound activation can be applied [LG2] (Figure 5.9), Anionic pentacoordinated silicon compounds are reduced to hydrogenosilanes by LAH or DIBAH [BC6]. 

The stabilization of the cation weakens the C-Si bond by the delocalization of electron density so that the bond is more easily broken. Attack of a nucleophile, particularly a halogen or oxygen nucleophile, on silicon removes it from the organic fragment and the net result is electrophilic substitution in which the silicon has been replaced by the electrophile. 

B. By oxidation Carbon-Phosphorus Bond Carbon-Silicon Bond Carbon-Halogen Bond Oxygen-Oxygen Bond Sulfur-Sulfur Bond... 

The most widely applicable method for the synthesis of silicon hydrides on a laboratory scale is the reduction of silicon-halogen, -nitrogen, or -oxygen bonds,... 

The number of covalent bonds formed by an atom is termed its COVALENCY. The covalency of an atom is equal to the number of electrons the atom needs to become isoelectronic with a noble gas. Some of the more common elements have the following covalencies when they follow the octet rule and also have no charge hydrogen and the halogens, 1 oxygen and sulfur, 2 nitrogen and phosphorus, 3 carbon and silicon, 4. LEWIS ELECTRONIC FORMULAS, in which bonds and unshared electrons are shown, are given for a few typical compounds of these elements ... 

Bromo- and iodosilanes are exceedingly sensitive to moisture, and very little water is needed to hydrolyse them. Both trimethylbromo- and trimethyliodosilanes have been used in organic synthesis because, with weak silicon halogen bonds, they readily cleave the carbon-oxygen bond to form siloxy derivatives. 

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