Chlorosilanes/metals

The Corrositex can be used to assess corrosivity of seven categories of chemicals acids, acid derivatives, acyl halides, alkylamines/polyalkylamines, bases, chlorosilanes, metal halides and oxyhalides. Therefore, if the test substance is found to be corrosive it can be assigned packing group criteria according to the US DOT regulations. 

The reductions of chlorosilanes by lithium aluminum hydride, lithium hydride, and other metal hydrides, MH, offers the advantages of higher yield and purity as well as dexibiUty in producing a range of siUcon hydrides comparable to the range of siUcon haUdes (59). The general reaction is as follows ... 

A small by-product stream is also realized in Europe from glass-etching by HF. Laboratory-scale production is readily accomphshed by exchange between metal fluorides and chlorosilanes (172). 

Silylnitronates 1 are prepared14-24,25 by metalation of primary nitroalkanes with lithium diisopropylamide and treatment of the lithionitronates with either chlorotrimethylsilane or (/er/-butyldimethyl)chlorosilane. Nonaqueous workup and distillation gives the silylnitronates in >75% yield as moisture sensitive, but thermally stable, products. (e/7-Butyldimethylsilylni-tronates are more stable than the corresponding trimethylsilyl compounds. 

The reaction of the carbonyl metallates with chlorosilanes (Eq. (5)) can be considered to be a nucleophilic displacement at the silicon followed by NaCl elimination. Several arguments support this view First of all, strong dipolar aprotic... 

Metal-induced reductive dimerization of carbonyl compounds is a useful synthetic method for the formation of vicinally functionalized carbon-carbon bonds. For stoichiometric reductive dimerizations, low-valent metals such as aluminum amalgam, titanium, vanadium, zinc, and samarium have been employed. Alternatively, ternary systems consisting of catalytic amounts of a metal salt or metal complex, a chlorosilane, and a stoichiometric co-reductant provide a catalytic method for the formation of pinacols based on reversible redox couples.2 The homocoupling of aldehydes is effected by vanadium or titanium catalysts in the presence of Me3SiCl and Zn or A1 to give the 1,2-diol derivatives high selectivity for the /-isomer is observed in the case of secondary aliphatic or aromatic aldehydes. 

To optimize the alkylation conditions, ferrocene was reacted with allyldimethyl-chlorosilane (2) in the presence of various Lewis acids such as aluminum halides and Group lO metal chlorides. Saturated hydrocarbons and polychloromethanes such as hexane and methylene chloride or chloroform were used as solvents because of the stability of the compounds in the Lewis acid catalyzed Friedel-Crafts reactions. The results obtained from various reaction conditions are summarized in Table IV. 

The ternary system consisting of a metallic catalyst, a chlorosilane, and a stoichiometric co-reductant has been reported by us for the first time to achieve the catalytic pinacol coupling. The homo coupling of aliphatic aldehydes is catalyzed by CpV(CO)4, Cp2VCl2, or Cp2V in the presence of a chlorosilane and Zn in DME to give the 1,3-dioxolanes 1 via the coupling and acetalization (Scheme 3) [18,19]. 

This method of silanation, which uses organic solvent without the addition of water, is suitable for highly reactive silane derivatives, such as chlorosilanes, aminosilanes, and methoxysilanes. This procedure will not work for ethoxysilanes, as these compounds are not reactive enough without prior hydrolysis to create the silanol. This method is convenient to use for silica particle modification and for the functionalization of metallic nanoparticles having the requisite—OH groups present (see Chapter 14, Section 5). 

In the cathodic reduction of activated olefins, chlorosilanes also act as trapping agents of anionic intermediates. Nishiguchi and coworkers described the electrochemical reduction of a,/ -unsaturated esters, nitriles, and ketones in the presence of Me3SiCl using a reactive metal anode (Mg, Zn, Al) in an undivided cell to afford the silylated compounds [78]. This reaction provides a valuable method for the introduction of a silyl group into activated olefins. 

Synthesis is typically by alkali metal-mediated coupling of dichlorosilanes or 1,2-dichlorodisilanes, although electrochemical coupling of chlorosilanes and dehydrocoupling of primary and secondary silanes also often lead to oligomeric (as opposed to high polymer) fractions. 

In addition to the unconventional methods of the formation of siloxane bonds such as those discussed earlier, the non-hydrolytic reactions of chlorosilanes in the presence of dimethyl sulfoxide, 7 and the reaction of dichlorosilanes with metal oxides,111 a new method has recently been discovered which involves the condensation of alkoxysilanes with organohydrosilanes with the release of hydrocarbon.112... 

Transition metal anions have widely been used in the synthesis of the first row transition metal derivatives of group IV metals however only in one case does the reaction take place with chlorosilanes... 

Dilithiated diamine 2 was synthesized by Karsch by a two-fold metalation of N,N,N, N tetramethylmethylenediamine (TMMDA) (1). The reaction was effected in n-pentane at low temperatures, yielding the poorly soluble Af,Af -bis(fithiomethyl)-Af,Af -dimethyl-methylenediamine (2) (Scheme 1). Due to its low solubility in toluene or THE, the highly pyrophoric compound was characterized by derivatization with several electrophiles, mainly chlorosilanes. Obviously, the addition of coordinating additives, such as TMEDA, DME (dimethoxyethane) or THE, does not enhance the solubility of the dilithium compound. Interestingly, as the author comments, TMEDA is only monolithiated in modest yields by alkyllithium bases. 

A dimerization reaction of alkenylmagnesium reagents in the presence of chlorosilanes, catalyzed by Cp2TiCl2, furnishing l,4-disilyl-2-butenes has been reported. Transition-metal-catalyzed carbon-carbon bond formation, promoted by Mn, Cr, Fe and Co, has been reviewed. ... 

Carbonation and subsequent hydrolysis of either lithiated or sodiated metallocenes lead to the corresponding carboxylic acids. Ferrocenecarboxylic acid and ferrocene-1,1 -dicarboxylic acid are readily produced in this manner and can be conveniently separated by extraction of the former with ethyl ether or benzene. The reaction of metalated ferrocenes with various chlorosilanes has led to a variety of triaryl- or trialkvlsilylferrocenes (3, 28, 90). 

Alkali metal hexafluoroantimonates arc used, like hexafluorophosphate or tetrafluoroborate salts, to effect halogen-exchange fluorination in organosilanes both in the presence and in the absence of solvents. Fluorotriphenylsilane and difluorodiphenylsilane are obtained in 87 and 95 % yield by heating the corresponding chlorides with sodium hexafluoroantimonate in tetra-ethylene glycol dimethyl ether (tetraglyme).102 Tetrafluoroborates react with chlorosilanes faster than hexafluorophosphate or hexafluoroantimonate salts. 

Metallated polystyrenes are versatile intermediates for the preparation of a number of polystyrene derivatives. Metallated polystyrene has been prepared from haloge-nated polystyrenes by halogen-metal exchange [41,42,65,66] and by direct metallation of polystyrene [67-69] (see Chapter 4). Electrophiles suitable for the derivatization of metallated polystyrene include carbon dioxide, carbonyl compounds, sulfur, trimethyl borate, isocyanates, chlorosilanes, alkyl bromides, chlorodiphenylphosphine, DMF, oxirane, selenium [70], dimethyldiselenide [71], organotin halides [69], oxygen [72], etc. [41,42,65-67],... 

Reaction with Further Electrophiles of Group IVA (Sl,Ge,Sn). IV-Silylated aziridines can be prepared from ethyleneimine by amination of chlorosilanes in the presence of an HC1 acceptor, by dehydrocondensation with an organosilicon hydride or by cleavage of a silicon—carbon bond in 2-furyl-, 2-thienyl-, benzyl-, or allylsilanes in the presence of an alkali metal catalyst (262—266). N-Silylated aziridines can react with carboxylic anhydrides to give acylated aziridines, eg, A/-acetylaziridine [460-07-1] in high yields (267). At high temperatures, A/-silylaziridines can be dimerized to piperazines (268). Aldehydes can be inserted... 

A number of metal and metalloid halides have been separated with rather conventional arrangements. For example, Keller and Freiser separated SnCl4, TiCl4, NbClj, and TaCIs at 200°C using a copper column packed with squalane on Chromsorb P (a modified diatomaceous earth).51 A variety of chlorosilanes and methylchlorosilanes have been separated using silicone oil plus diethyl ph-thalate as the stationary-phase and thermal conductivity detectors.52... 

In contrast to fluorosilanes with pentacoordinate silicon systems such as 235-237, it is very difficult to find similar compounds of chlorosilanes to establish the Si—Cl bond length in similar cases. X-ray crystal structure is available for only few of these compounds and only typical cases of the shortest and longest Si—Cl bonds are given. The shortest bond lengths are found in compounds where the silicon is bonded to a metal such as... 

The most convenient method to prepare metalated arylsilanes is the reaction of a chlorosilane with lithium or potassium in polar solvents such as THF or DME (Scheme 2). 

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