Oxygen—silicon bonds reactions with

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 ... 

Less usual carbosilane dendrimers were synthesised by reaction of acetyl-protected hydroxyethyl glycosides with chlorosilanes. Introduction of the carbohydrate component proceeds via alcoholysis of the chlorosilane with formation of silicon-oxygen bonds a carbosilane core unit is formed with carbosiloxane side arms [82]. Reverse assembly of carbosilanes with a carbohydrate core is also feasible [54]. 

The reaction is an equilibrium with the strength of the silicon-oxygen bond normally favouring the silyl ether. In some cases, however, the reverse reaction may be observed. An example of such a reaction is given in Equation Si 1.4. 

If the 1,5-diearbonyl compound is required, then an aqueous work-up with either acid or base cleaves the silicon-oxygen bond in the product but the value of silyl enol ethers is that they can undergo synthetically useful reactions other than just hydrolysis. Addition of the silyl enol ether derived from aeetophenone (PhCOMe) to a disubstituted enone promoted by titanium tetrachloride is very rapid and gives the diketone product in good yield even though a quaternary carbon atom is created in the conjugate addition, This is a typical example of this very powerful class of conjugate addition reactions. 

The basic idea in Osseo-Asare s model is that when protons, hydroxyl ions, ligands, or water molecules bind to the surface sites, they cause a polarization of the underlying silicon-oxygen bonds. With a sufficient number of bound species, the Si-O-Si bonds become sufficiently weakened to permit detachment of the surface silicon ion. In the absence of ligands, the dissolution rate is determined by the surface concentration of protonated species (MOH 2> at pH < pzc, of water at pH pzc, and of deprotonated species (MO ) at pH > pzc. The surface charge is modulated by the protons in the solution immediately adjacent to the solid surface according to the reactions... 

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