Halosilanes reactions

Alkali-metal deuteride reduction of halosilanes produces deuteriosilanes readily, but yields are less than from LiAlD, halosilane reactions ... 

Synthetic alkali metal or alkaline earth metal silicoaluminate rendered hydrophobic by reaction with halosilane, Reaction made in the oil... 

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. 

The heat of reaction of tetrachlorosilane with an excess of water is 290.0 kJ /mol (69.3 kcal/mol). The reaction of tetraduorosilane with excess water contrasts with the other halosilanes, because it leads to formation of hexaduorosiUcic acid and a hydrous siUca. 

The reaction of halosilanes with alcohols proceeds analogously. Dihinctional amines react with tetrahalosilanes to yield tetrakis(dialkylamino)silanes. 

Organometalhcs. Halosilanes undergo substitution reactions with alkali metal organics, Grignard reagents, and alkylaluininums. These reactions lead to carbon—siUcon bond formation. 

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... 

An alternative method for preparing phosphinous amides makes a profit on the high affinity between silicon and halogen atoms. This is the driving force of the reactions between halophosphanes and Ar-(trimethylsilyl)anilines, AT-(tri-methylsilyl)amides or AT-(trimethylsilyl)ureas and thioureas, as represented in the Scheme 6. In these processes the desired P-N bond and an halosilane are simultaneously formed [53,58-60]. 

Silicon substituents can be introduced into alkenes and alkynes by hydrosilation.70 This reaction, in contrast to hydroboration, does not occur spontaneously, but it can be carried out in the presence of catalysts such as H2PtCl6, hexachloroplatinic acid. Other catalysts are also available.71 Halosilanes are more reactive than trialkylsilanes.72... 

While trifluoro and other halosilanes function by increased electrophilicity at silicon, nucleophilic reactivity of allylic silanes can be enhanced by formation of anionic adducts (silicates). Reaction of allylic silanes with aldehydes and ketones can... 

An important reaction of silicon compounds containing electronegative substituents, such as the halogens or a Group 15 or 16 element, is hydrolysis, which often occurs very readily even with atmospheric moisture. The primary reaction in silicone production is the hydrolysis of halosilanes, usually the readily available chlorosilanes, to give silanols, which then undergo acid-catalyzed condensation with loss of water, as shown in Scheme 1. 

The reaction of phenyldisilanes PhnSi2H8 n and phenyltrisilanes PhnSi3H8 n with hydrogen halides [5] poses an inherent problem which is the formation of azeotropic mixtures between benzene (generated during the reaction) and the halosilanes. The use of mesityldisilanes and 1-naphthyldisilanes completely avoids these difficulties. 

II) Silylhydrazines are formed in the reaction of hydrazine with halosilanes. They react with BuLi to yield mono- and dilithiated derivatives (6, 8) [4-7]. 

An important method of preparing cyclic siloxanes and aminosiloxanes involves metallation of functionalized silanols, aminosilanols, or siloxanols followed by treatment with appropriate halosilanes. Intra- and intermolecular ring closure reactions are possible [10]. 

Six-membered rings are either formed by thermal LiF-elimination of lithiated fluorosilanols [10] or by the reaction of siloxandiolates with halosilanes, e.g. ... 

The rate of step 4 involving elimination of halosilane also depends on the nature of the halogen atom but in the inverse order F < < Br. For Hal=Br, intermediates (32) are impossible to detect. By contrast, for Hal=F, elimination of Si F is the rate-determining step, which requires a special procedure, for example, refluxing of intermediate (32) (Hal=F) in acetonitrile for 1 h. (Preliminary data show that the microwave technology makes it possible to sharply decrease the time required for completion of step 4 (90)). A decrease in the elimination rate in the series F < < Br is evidence that this reaction is not... 

Although halosilanes undergo smooth nucleophilic substitution at the silicon, they are rather inert to redox reactions. Therefore, chlorosilanes are usually used as trapping agents of anionic intermediates generated by electroreduction of organic compounds. However, in the absence of other reactive substrates halosilanes are reduced electrochemically to form Si-Si bonds. Indeed, there are a number of reports in the literature of the cathodic reduction of chlorosilanes (Sect. 4.2). 

In the absence of other substrates which are easily reduced, halosilanes can be reduced by cathodic reaction. However, it is rather difficult to determine the reduction potentials of halosilanes, because halosilanes are readily hydrolyzed during voltammetric measurements. Although early reports stated that the reduction potential of Me3SiCl is not very negative, extensive studies by Corriu... 

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,... 

Silyl alkyl and silyl aryl peroxides 7 are prepared by reaction of alkyl, aryl or aralkyl hydroperoxides with halosilanes (equation 12). Such reactions are carried out in an inert solvent in the presence of an acid acceptor, such as pyridine, ammonia or a tertiary amine in ether or petroleum ether (Table 3) . ... 

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. 

Caution. Owing to the lachrymatory properties of bromine reagent and halosilane product, this reaction should be carried out in a well-ventilated hood. 

As part of a study to elucidate the mechanisms of reactions of complexed halosilanes, we discovered that N,N,N, N -tetraethylethylenediamine (teeda) reacts with trichlorosilane in an unexpected fashion to give [SiH2Cl2 teeda]. 

Reaction of ot-halocarbanions with aldehydes. The reaction of a- or (3-poly-halosilanes with 1 at 25° generates halocarbanions which are sufficiently stable to undergo addition to aldehydes in moderate to high yield. 

As outlined in our previous review (5), coupling reactions of a nucleophilic reagent Nu with an organosilane RaSi—X occur only by a one-stage nucleophilic mechanism [Eq. (1)]. The halosilanes are not prone to one-electron transfer which could lead to a two-stage mechanism [Eq. (2)]. 

A reaction related to the nucleophile-catalysed hydrolysis of silanes is the nucleophile-catalysed racemization of silanes. The racemization of a range of halosilanes was found to have an order with respect to nucleophile varying from 1 to 346,47. The reactions have entropies of activation which are large and negative, and enthalpies of activation which are small and sometimes negative. Both racemization and hydrolysis are slowed by increasing steric crowding at silicon.48... 

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