Silicon halides, synthesis

The chemistry of silicone halides was recently reviewed by Collins.13 The primary use for SiCU is in the manufacturing of fumed silica, but it is also used in the manufacture of polycrystalline silicon for the semiconductor industry. It is also commonly used in the synthesis of silicate esters. T richlorosilane (another important product of the reaction of silicon or silicon alloys with chlorine) is primarily used in the manufacture of semiconductor-grade silicon, and in the synthesis of organotrichlorosilane by the hydrosilylation reactions. The silicon halohydrides are particularly useful intermediate chemicals because of their ability to add to alkenes, allowing the production of a broad range of alkyl- and functional alkyltrihalosilanes. These alkylsilanes have important commercial value as monomers, and are also used in the production of silicon fluids and resins. On the other hand, trichlorosilane is a basic precursor to the synthesis of functional silsesquioxanes and other highly branched siloxane structures. 

Herzog, U. Organosilicon Halides - Synthesis and Properties. In The Chemistry of Organic Silicon Compounds Rappoport, Z., Apeloig, Y., Eds. ... 

The reactions of silicon halides with organomagnesium or organolithium compounds for the synthesis of organosilicon compounds are oversimplified in Eqs. (3) and (4). If several reactive groups are attached to the silicon atom, as in C2H5SiCl3, the reaction cannot be controlled so as to yield a particular substitution product, since all possible substitutions will occur simultaneously. All that can be done is to favor the yield of the desired compound by manipulation of reaction conditions. 

Silyl cyclopentadienes1,2 3 have been formed through the interaction of a cyclopentadienide prepared in situ with an appropriate silicon halide however, purification of the desired product required filtration, removal of solvent, and vacuum distillation at elevated temperatures. The synthesis of the silicon compounds, C5H5(SiH3) and C5H4(CH3)(SiH3), described here utilizes a low-temperature reaction between liquid bromosilane and the salt K[RC5H4] (where R = H, CH3), in a 1 2 mole ratio, respectively.4 5... 

Much of the early work on the synthesis of organosilicon compounds was based on reactions between Grignard reagents and silicon halides (and to a lesser extent on silicate esters), and much effort was devoted to optimizing stepwise reactions ... 

These results led Schumb and Sailer to devise a two-stage synthesis 6 which allows a much better control. The sodium first is allowed to react with a halide such as chlorobenzene in a solvent to yield phenyl sodium. After the heat of this reaction is dissipated, the phenyl sodium is mixed with the silicon halide in solution, and a milder reaction ensues. In this way hexaphenyldisilane was made from hexachlorodisilane, and hexaphenyldisiloxane from hexachlorodisiloxane. Moreover, phenyltrichlorosilane was made by the action of less than one equivalent of sodium phenyl on silicon tetrachloride. The use of a separately prepared sodium alkyl in this way provides the same degree of control as in a Grignard synthesis, and the reactions indeed are very similar. Organolithium compounds probably could be used in the same way. 

The diruthenium and diosmium species M2(SiMe3)2(CO)g are obtainable in high yield and are reduced by sodium amalgam to [M(SiMe3XCO)4] , whose reactions with various halides provide a route to silicon-metal complexes - . Addition of silicon halides to [M(CO)4] " is successful only in the synthesis of Fe(SiH3)2(CO)4 (see 5.8.3.3.1.) and is not a route generally available for M(SiR3)2(CO)4. 

Silicon halides react with complex hydrides to form silanes. Complex hydrides used are LiAlH and to a lesser extent MBH (M = Li, Na, K) . Reductions are carried out in aprotic ether solvents, e.g., Et O, glymes, THE or n-BUjO. These reactions are adaptable to Si—D bond synthesis (see 1.6.7.1.2). Typical syntheses of monosilanes are shown in Table 1. Chlorosilanes are preferred the fluorides react less readily. Bromo- and iodosilanes react easily but offer no advantage over the more available chlorides. ... 

In this section we discuss the synthesis of tri- and tetraorganylsilanes. A routine method to obtain tetraorganylsilanes is the reaction of lithiated alkyl compounds with silicon halides which affords the desired organylsilanes (equation la) with yields of up to 97%—illustrated by the synthesis of tetrabutylsilane (3) (equation lb)21. Alternatively,... 

The synthesis of organosilicon compounds (i.e., formation of the Si—C bond) starting from a silicon halide and an organometallic compound (RMgX, LiR) (9, H, 60) is well known ... 

Silicon tetraalkyl and tetraaryl derivatives (R4Si), as well as alkyl or aryl silicon halides (R SiCl4 , n = 1-3) can be prepared by reaction types 18.38-18.42. Note that variation in stoichiometry provides flexibility in synthesis, although the product specificity may be influenced by steric requirements of the organic substituents. Reaction 18.38 is used industrially (the Rochow process). 

Organosilicon compounds can be prepared by reaction of silicon halides with other organometallic compounds. The first such synthesis (1865) was that by Friedel and Crafts270 who heated silicon tetrachloride with dimethyl-zinc in a sealed tube at 200° ... 

However, the most far-reaching and almost universally applicable method for synthesis of organosilicon compounds is by the action of Grignard reagents on silicon halides. With silicon tetrachloride this gives a mixture of products in which one to four chlorine atoms have been replaced by hydrocarbon groups ... 

There is another synthesis of organosilicon halides, not generally applicable, but important in industry because the starting materials are cheap this is the treatment of silicon halides with hydrocarbons at high temperatures. As examples, tetrachlorosilane and benzene in the gas phase at 840° give dichloro(diphenyl)silane 372 tetrachlorosilane and methane in the gas phase give trichloro(methyl)silane at 960° in the presence of an iron catalyst372 and at 500° in the presence of a brick or pumice catalyst.373... 

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