Halosilanes synthesis

Dkect synthesis is the preparative method that ultimately accounts for most of the commercial siUcon hydride production. This is the synthesis of halosilanes by the dkect reaction of a halogen or haUde with siUcon metal, siUcon dioxide, siUcon carbide, or metal sihcide without an intervening chemical step or reagent. Trichlorosilane is produced by the reaction of hydrogen chloride and siUcon, ferrosiUcon, or calcium sihcide with or without a copper catalyst (82,83). Standard purity is produced in a static bed at 400—900°C. 

Basically the same methods known from the synthesis of classical metal-silyl complexes can also be applied to the preparation of low valent Si compounds. The procedures given here are summarized with the focus on silylene complexes These are a) reactions of appropriate metal anions with halosilanes, which are the most important methods for the formation of M-Si bonds. Alternatively, silyl... 

The properties and applications of five commercially important groups of silanes those containing Si-H (hydride functional silanes), Si-X (halosilanes), Si-C (organosilanes), Si-OSi (siloxanes), and Si-OR (silicon esters) are thoroughly discussed by Arkles.14 As the role of functional siloxanes grows, so does the importance of the hydrosilylation reactions in this field. A broad introduction to hydrosilylation processes as applied to the synthesis of silicone precursors and to the functionalization of siloxanes is provided in the earlier editions of COMC, and,... 

Disilathianes, for example (SiH3)2S and [(CH3)3Si] 2S, have been prepared by several routes, namely, the reaction of iodosilane with silver8 and mercuric2 sulfides halosilanes with lithium sulfide,7 [NH4]SH,9 and [Me3NH]SH7 disilaselenane with H2S10 and trisilylphosphine with sulfur.10 Recently, the synthesis of hexamethyldisilathiane, [(CH3)3Si] 2S, was described from the protolysis of l-(trimethylsilyl)imidazole with H2S and from the dehydrohalogen-ation of chlorotrimethylsilane and H2S with a tertiary amine.11 Both of these methods require about 18 hours. 

Isocyanates and isothiocyanates both react with water in a manner similar to the halosilanes to give hydrated silica. They also react with primary and secondary amines to give silylamines which, on hydrolysis, afford A-mono- and N,N-disubstituted ureas and thioureas (Scheme 31), which is a useful synthesis of these compounds. ... 

As a general mle, unless an anion-stabilizing group, such as phenyl, or a heteroatom such as sulfur is present, the alkylsilane is not readily deprotonated. The a-halosilane can be deprotonated but, unlike the readily available chloromethyltrimethylsilane, there are few general methods to this approach. Al-kyllithium reagents add to vinylsilanes ( ) to produce the carbanion (287). Silyl derivatives with heteroatoms, such as sulfur, selenium, silicon or tin, in the a-position (288) may be transmetallated (Scheme 41). Besides the difficulty in synthesizing the anion, alkene formation lacks specificity for simple di- and tri-alkyl-substituted alkenes. As a result, the Peterson reaction of an a-silyl carbanion with a carbonyl has found the greatest utility in the synthesis of methylene derivatives, (as discussed in Section 3.1.3), heterosubstituted alkenes and a,p-unsaturated esters, aldehydes and nitriles. 

Since the preparation of anionic species or organosilicon compounds is largely restricted by its reaction conditions, the synthetic utility of silyl anions for the synthesis of organosilicon compounds is limited. However silyllithiums possessing one or more phenyl groups on a silicon atom are readily prepared by the reductive metallation of the corresponding halosilanes with lithium. Allylsilanes are synthesized by the reaction of allyl acetates with the cuprate prepared from such a reagent (eq (47)) [43]. 

Practically all of the above reactions have, with some variation in the halosilane, been applied to the synthesis of higher polysilanes. Reactions which are strictly analogous to those described above have been employed in the synthesis of tetra- and hexasilanes. 

The two most general means of synthesis of organosilanes are nucleophilic displacement of halogen from a halosilane by an organometallic reagent and addition of silanes at double or triple bonds (hydrosilation). Organomagnesium and organolithium compounds... 

A method for the preparation of halosilyl carbamates and isocyanate involves direct synthesis from amines via halosilyl carbamate intermediates [277]. A primary amine is converted to its carbamic acid salt, which is then treated with a silane containing > 2 halogen atoms bonded to Si. Gentle heating of the resulting halosilyl carbamate gives the isocyanate. In an alternative (exchange) procedure, the carbamic acid salt is treated with any halosilane to form a silyl carbamate, which is trans-silylated. 

Interestingly bismuth(III) halides (BiXs with X = Cl, Br, I) have been found to be efficient catalysts for the activation of halosilanes leading to their use as halogenating agents [17a,bj. Using polychlorosilanes, polysiloxanes have been obtained. This unprecedented exaltation of the Si-Cl bond has found an application in the synthesis of a series of -halo ketones and esters [17cj. 

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