Silanes with halogens

Some inorganic cyclic silanes with halogen substituents have been investigated, thoug their properties are almost unknown, and even their existence is controversial. 

Silanes with electronegative ligands did not react, except in the presence of the tertiary base EtjN [e.g., Eq. (19)] (62, 63). This then provides an attractive route to Si—Pt(II) compounds since the starting materials are readily available and the reaction gives pure products in high (60-90%) yields. Only aromatic phosphine Pt complexes reacted readily, and the use of an excess of silane failed to bring about replacement of the second halogen atom. 

MRH Bromine 1.21/91, carbon tetrachloride 2.89/83, chlorine 3.85/82 Silane burns in contact with bromine, chlorine or covalent chlorides (carbonyl chloride, antimony pentachloride, tin(IV) chloride, etc.) [1], Extreme caution is necessary when handling silane in systems with halogenated compounds, as a trace of free halogen may cause violent explosions [2],... 

Several reactions of halogen-substituted carbon-centered radicals with silanes have been studied, but limited kinetic information is available for reactions of halogen-substituted radicals with tin hydrides. A rate constant for reaction of the perfluorooctyl radical with Bu3SnH was determined by competition against addition of this radical to styrenes, reactions that were calibrated directly by LFP methods.93 At ambient temperature, the n-C8F17 radical reacts with tin hydride two orders of magnitude faster than does an alkyl radical, consistent with the electron-deficient nature of the perflu-oroalkyl radical and the electron-rich character of the tin hydride. Similar behavior was noted previously for reactions of silanes with perhaloalkyl radicals. 

The kinetic data for halogenated carbon-centred radicals with silicon hydrides are also numerous and a few examples are shown in Table 3.2. The kinetic data for perfluoroalkyl radicals were obtained by competition of the appropriate silane with the addition to an olefin [16-18]. The kinetic deuterium isotope effects (/ h/ d) on the attack of on the Si—D bond of... 

Silane reacts explosively with halogens at ordinary temperatures forming halogenated silane derivatives. Reaction is vigorous to moderate at very low temperatures ... 

To resolve this dilema, we propose that the polymer is interacting with the additive in the excited state, (27) perhaps via electron transfer, and that this interaction leads to the irreversible degradation of the polymer. The direct interaction of photoexcited monomeric polysilanes with halogen derivatives resulting in the cleavage of Si-Si bonds had been reported (28). In a similar fashion, we must conclude either that this interaction does not occur with the alkyl silane polymers or that it does not result in rapid polymer degradation. 

The trimethylsilylated ylides (1), easily generated from trimethyl chlorosilane and ylides, react with aldehydes 2 to form vi-nylsilanes 3 (2,3). The vinylphosphonium silanolates 4 are also formed. Compounds 3 are versatile reagents for further reactions (4). The ylide J (with R1 =H) reacts with aldehydes 2 to give the dienes j). The oxidation of with the adduct 6, from triphenyl-phosphite and ozone, gives access to a generaT synthesis of acyl-silanes (trimethylsilylketones) (2). The silylated ylides react to form phosphonium salts 7 with halogen compounds. The salts 7.can be desilylated by fluorine ions. The disubstituted ylides JO Tormed can be converted in statu nascendi with aldehydes V[ into the tris-substituted olefin J2 (2,3). In the case of R3-I, vinyl... 

Additional CaSi reactions were carried out with halogens, PC15, and other halogenating agents. In all cases a decomposition of the silicon chains to monomeric silane derivatives occurred before reaction of the calcium was complete, so no definable products could be obtained. 

For the synthesis of the known two poly(lithiomethyl)silanes the halogen-lithium exchange (for 1 [2]) and the reductive cleavage of C-S bonds with lithium (for 3 [3]) were used [4] (Scheme 1). 

Condensation of Hydro silanes with Hydrocarbons and Halogenated Hydrocarbons... 

SAFETY PROFILE Mildly toxic by inhalation. Silanes are irritating to skin, eyes, and mucous membranes. Easily ignited in air. Explosive reaction or ignition on contact with halogens or covalent halides (e.g., bromine, chlorine, carbonyl chloride, antimony pentachloride, tin(TV) chloride). Ignites in oxygen. Can react with oxidizers. 

By reaction oftrimethyl(trifluoromethyl)silane with difluorophosgene or trifluoroacetyl fluoride in the presence of a compound possessing an active halogen, the O-anion thus generated reacts further to give the product of the substitution of this halogen, c.g. 19.Dl-53 58 6t> 104 105... 

Apart from the reaction with halogen derivatives, use was also made, for the synthesis of silicon-containing cellulose esters, of the reaction of alcoholysis, with cellulose, of tetraalkoxysilanes or alkyl(aryl)trialkoxy-silanes and the amides of siliconic acids (64) ... 

To elucidate the question whether or not cyclosilane structures are essential for the color and fluorescence of the polymers, linear and cyclic silanes with silicon halogen or -triflate functions were prepared and hydrolyzed to siloxene-like structures. 

A convenient method for the preparation of penta- and hexacoordinate silicon complexes was recently developed and reported [1]. The synthesis was based on an exchange reaction between poly-halogenated silanes with the O- or A-trimethylsilylated acylhydrazines and led to the formation of (0-Si)- and (N-Si)- mono and bis- chelate complexes (Scheme 1). 

Carbon-silicon bonds can be formed by treating the lithio intermediate with halogen-containing silanes (Reaction 22) (28). Carbon-phosphorus bonds can be prepared similarly (Reaction 23) (29). 

The treatment of an amino acid per se by means of halogenoorganylsilanes cannot be accomplished, since the formation of dipolar ions eNH3CHRCOOe impedes any reaction with halogenated silanes. Hence, a viable approach is to esterify the amino acid first to 474 and then convert it in the presence of a HC1 acceptor into the corresponding N-TMS-amino acid (475) (equation 225)240,241. Another method is to employ the sodium salts of amino acids (476) which yields iV-TMS-amino acid TMS-ester (477) (equation 226)242. 

The perphenylcyclosilanes, (Ph2Si)4 and (Ph2Si)5, can be cleaved with halogenating agents, hydrogen halides or alkali metals to give linear silanes ... 

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