F Dichlorosilane

Summary Several lithium l,3-diphospha-2-sila-allyl complexes 3a-f and the diphosphino-dichlorosilane 2 have been prepared and characterized. The hydrolysis and substitution reactions of these compounds are described yielding a number of phosphino- and diphosphino-silaphosphenes 5a-d, 4a,b and 6. The compounds have been characterized by NMR and by X-ray analyses in the cases of 2, 3a-c and 4a. 

The coupling of dichlorosilanes (30 mmol) with excess of Me3SiCl (10 mol. eq.) led, after the passage of 4.2 F moP, to the respective trisilanes (Eq. 9) in isolated yields much higher than those obtained from chemical routes (Table 3). Both, A1 and Mg anodes gave similar results. 

Chlorosilane derivatives in the presence of magnesium undergo fran -addition to the 4,5-double bonds of ethyl 1/f-azepine-l-carboxylate <83B(H175>. For example, the reaction with dimethyl-dichlorosilane, after treatment with water during workup, gives (32), which loses water to form the cyclic derivative (33). The reaction is considered to proceed by way of the radical anion (34) formed by one-electron transfer from magnesium. 

Silicon nitride is usually deposited using one of the following silicon precursors silane, dichlorosilane, trichlorosilane, or silicon tetrachloride. Silicon tetrachloride, the most common silicon precursor, is used with an ammonia and nitrogen mixture to obtain silieon nitride at temperatures of 800 to 1,400X (1,472 to 2,552 F). Silicon carbide is usually produeed by cracking methyl trichlorosilane at 800 to 1,400°C (1,472 to 2,552 F). 

The intermediacy of silylenes, equivalent to carbenes, is suggested from hindered dichlorosilanes, e.g., dimesityldichlorosilane.2i6 Their sonochemical dimerization gives tetramesitylsilene in ca, 90% yield instead of 20% electro-chemically. The reaction of di-f-butyldichlorosilane, in the presence of triethyl-silane as a trapping agent, gives mainly the symmetrical disilane with sodium or potassium but also the product of insertion into the Si-H bond with lithium, in 85% yield. In the presence of an olefin, the intermediate is trapped to give silacyclopropanes stereoselectively.2i7 Sonication is essential for success. 

Note The measured autoignition temperature of dichlorosilane is above 212°F (100°C), but accumulated ... 

Dichlorosilane is a highly flammable, corrosive, and toxic gas at room temperature and atmospheric pressure. It causes severe bums on contact with eyes, skin, and mucous membranes. With water or moisture, it hydrolyzes rapidly to yield silica and silicon oxyhydride along with hydrochloric acid. It is shipped as a liquefied gas in low pressure cylinders at its vapor pressure of 9.1 psig (62.7 kPa) at 70°F (21.1°C). It can form flammable mixtures with air and oxidizing agents. 

Because of reactivity with.water, dichlorosilane should always be handled in dry equipment with a dry inert gas, such as nitrogen. For transfer service, dry inert gas is preferred to pumping. Some examples of other common compatible materials used include Viton, Teflon, Kel-F, nickel. Monel, and some types of stainless steel. 

The most common cylinder valve used for dichlorosilane is a stainless steel diaphragm valve with a Connection CGA 678 outlet. The cylinder valve body has a combination CG-4 type pressure relief device consisting of a fusible metal plug, melting about 165°F (74°C), which is protected from the cylinder contents by a frangible metal disk, i.e. a rupture disk, rated at 250 psig (1724 kPa). 

Dichlorosilane Product Information Sheet (F-4190), Union Carbide Corporation, Linde Division, 39 Old Ridgebury Road, Danbury, CT 06817. (1980) Encylopedie Des Gaz L Air Liquide. Elsevier/North-Holland Inc., 52 Vanderbilt Avenue, New York, NY 10017. 

To reduce the inductive effect on the Si—C bond, the perfluorinated group has to be isolated from the silicon atom. Fluorination of an alkylsilane even in the P position yields hydrolytically unstable compounds which undergo thermal rearrangements and liberate Cp2=CR2- Fluorination of an alkyl group in the 7 position, CF3CH2CH2—, does not affect the Si— F bond significantly and the hydrolytic stability is adequate for practical use [132]. The dichlorosilane CF3CH2CH2Si(CH3)Cl2 hydrolyzes to form a polysiloxane. However, the ethylene link increases the bulkiness of the side chains, increases the hydrocarbon/flu-orocarbon ratio, and causes fluorocarbon-hydrocarbon and fluorine-silicone interactions and orientation effects which may reduce the surface activity of the fluorinated compound. 

Knowing that the reduction potentials of dichlorosilanes are much less cathodic than that of Me3SiCl, we can assume that the dichlorosilanes are first reduced to monochlorosilyl anions which are then trapped by the Me3SiQ present in large excess rather than by the dichlorosilane. Moreover, the kinetic curves (obtained from GC analysis) of the electrochemical reduction of PhMeSiCl2 with an A1 anode, as an example, show that the two silicon-chlorine bonds are reduced in two well-separated steps that is the monochlorinated disilane was formed initially until 2.1 F/mol of PhMeSiCl2 had been consumed (Equations 11, Figure 4). 

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