Preparation of Organosilicon Compounds

Substitution by Alkyls of Zinc, Mercury, and Aluminum. The reaction of alkyls of zinc with ethyl silicate or silicon tetrachloride was the first to be used for the preparation of organosilicon compounds. During the period 1863 to 1880 Friedel and Crafts and later Ladenburg employed zinc dimethyl and zinc diethyl to prepare the corresponding alkyls of silicon and many of the intermediate substitution products as well. The reactions were conducted in sealed tubes heated to about 160° and were of a straightforward metathetical type ... 

A further method often used for preparation of organosilicon compounds is a Wurtz-type synthesis in which a silicon tetrahalide is condensed with an alkyl or aryl halide by means of metallic sodium in ether or a hydrocarbon solvent 313... 

The possibility of the existence of organosilicone compounds was first predicted by Dumas in 1840, and in 1857 Buff and Wohler found the substance now known to be trichlorosilane by passing hydrochloric acid gas over a heated mixture of silicone and carbon. In 1863 Friedel and Crafts prepared tetraethylsilane by reacting zinc diethyl with silicon tetrachloride. 

During the last three decades, a number of organosilicon compounds have been prepared which have opened new vistas in the synthesis of numerous organic compounds and have brought to light many fascinating reactions. 

The study of the antitumorous effect of low-toxic silatranes not affecting healthy organs and tissues and producing a certain antiblastic effect in the tests with animals indicates the necessity of further investigation of this class of organosilicon compounds in order to develop a new type of anti-cancer preparations. 

Since 1989, when the first volume of The Chemistry of Organosilicon Compounds appeared1, large strides have been made in preparing silicenium cations. The first X-ray structures2,3 of solvent stabilized silicenium cations are among the most notable successes. Most recently, a free silicenium cation has been prepared in solution4 5. In addition... 

The entire area of organosilicon chemistry blossomed with Kipping s preparation of such compounds by the more convenient Grignard process. These silanes turned out to be of paramount importance since they hydrolyzed readily to form compounds containing Si-0 bonds, both linear and cyclic.12,22,24 28 These new materials were first called silicoketones or silicones by analogy with ketones in the organic area. Structural studies, however, showed that they did not contain the Si=0 double bond. Thus, the silicone name is a misnomer, but it has persisted, at least in casual usage. However, the terms siloxanes and polysiloxanes are preferred. 

These syntheses of all three elements have been widely used — those of organoboron compounds often as a prelude to further transformations (see Section 15.4, Ref. [1]), those of organosilicon compounds often to characterize organomagnesium reagents, and those of organophosphorus compounds often to prepare phosphine ligands. 

As outlined in the previous chapters, the preparation of silicone polymers involves first the preparation of organosilicon halides or esters, secondly the hydrolysis of an appropriate mixture of these intermediates, and finally the condensation or rearrangement of the polymers to achieve the desired molecular arrangement. Only in the first step is there a choice of preparative methods the second and third steps are carried out in much the same way, regardless of how the intermediates were made. From the standpoint of synthesis, the problem therefore comes down to the preparation of the methyl-, ethyl-, and phenylchlorosilanes or ethoxysilanes. Of these the methyl compounds are the most important, because they are used directly for the water-repellent treatment and are the only intermediates required for the oils, elastomers, and some types of resin. 

Intermediate. A reactive compound containing an essential grouping which, by further processing or reaction, is conveyed to the finished product here, a reactive organosilicon compound of relatively simple structure which is used in the preparation of organosilicon polymers. 

As discussed above, the cross-coupling reaction of organosilicon compounds proceeds stereospecifically, depending on the reaction conditions. Thus, the transformation C—Si C —C is demonstrated to be accompanied by chirality transfer. Now, the question arises of how to prepare organosilicon compounds whose chiral allylic carbon is substituted by a silyl group. The most accessible solution is asymmetric hydrosilylation of olefins [35]. We studied asymmetric hydrosilylation of 1-substituted 1,3-butadienes using... 

Species that combine the properties of organosilicon compounds and phos-phazenes are prepared by the linkage of organosilicon side groups to a small molecule cyclic or linear high polymeric phosphazene skeleton. This is particularly important for high polymeric derivatives in which hybrid properties typical of polysiloxanes (silicones) and polyphosphazenes - may be obtained. 

Uses of organosilicon compounds in preparative organic chemistry... 

Silicon compounds with coordination number larger than four are the object of many studies first with respect to their application as catalysts in organic and inorganic syntheses and second as starting materials for the preparation of a broad variety of organosilicon compounds [1]. Additionally, hypervalent silicon hydride compounds can successfully be used as model compounds to study, for instance, the mechanism of nucleophilic substitution reactions, which is of great interest since the silicon atom is able to easily extend its coordination number [1]. Moreover, hypervalent silanes are suitable as starting materials for the synthesis and stabilization of low-valent silanediyl transition metal complexes [2-5]. 

Summary The development of materials with well-designed surface properties becomes increasingly important in many technological applications. Our studies particularly focus on the preparation and application of organosilicon compounds... 

For the preparation of technically important metal carbide and metal nitride materials the application of organosilicon compounds as preceramic precursors is advantageous under certain conditions [1-5]. Compared with the conventional metallurgical powder process, one benefit is the utilization of very low process temperatures for the preparation of individual ceramic materials. Another improvement is the high purity of the ceramics obtained from tailor-made preceramic precursors. Usually, after pyrolysis organosilicon compounds afford silicon-containing ceramic powders Likewise, they can also be used under certain conditions for the production of silicon carbide or silicon nitride fibers. 

Colvin, E. W. Preparation and use of organosilicon compounds in organic synthesis. Chem. Met-Carbon Bond 1987,4, 539-621. 

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