Silicon with activated alkyl chlorides

III. Direct Reaction of Elemental Silicon with Activated Alkyl Chlorides. 160... 

Recent studies on the direct reaction of elemental silicon with alkyl chlorides such as methyl chloride, activated alkyl chlorides, polychloro-methanes, (chloromethyl)silanes, (dichloromethyl)silanes, etc. are summarized in this review. In the direct reaction of elemental silicon with activated alkyl chlorides and polychloromethanes, the decomposition of the reactants can be suppressed and the production of polymeric carbosilanes reduced by adding hydrogen chloride to the reactants. These reactions provide a variety of new organosilicon compounds containing Si-H and Si- Cl functionalities, which should find considerable application in the silicone industry. 

Thousands of papers and patents have appeared on the direct synthesis of organochlorosilanes since 1940 when Rochow reported the direct reaction.4 These results are comprehensively accounted for in a number of earlier reviews and books.3 8 The purpose of this review is to describe the recent developing trend of the direct reaction of elemental silicon with activated or unactivated alkyl chlorides, in particular, emphasizing direct reactions with a mixture of hydrogen chloride and activated alkyl chlorides such as polychlorinated methanes, silylmethyl chlorides and dichlorides, allyl chloride, etc. 

More than 60 years after its simultaneous discovery by Rochow and Muller, the direct reaction of copper-activated silicon with alkyl chlorides is arguably still the most important industrial process for the preparation of basic organosilanes. An inspiring historic account highlighting the significance of this seminal work has been given by Seyferth.12 A comprehensive review on the subject has been written by Jung and Yoo.13 The most recent work associated with the direct process is concerned with the role of metallic promoters, such as Zn and Cd, as well as mechanistic aspects.14... 

In the reaction with ferrocene, allyldimethylchlorosilane reacts at 0 °C, allyl-(methyl)dichlorosilane reacts at the reflux temperature of methylene chloride, but allylsilanes containing two or more chlorine substituents at the silicon do not give alkylation products. In alkylations of ferrocene, allyldimethylchlorosilane shows the highest activity, allyl(methyl)dichlorosilane is less reactive, and allylsilanes containing two or more chlorine-substituents at the silicon have no activity. Allyl-trimethylsilane reacts with both benzene and ferrocene to give allylsilylation products but no alkylation product. 

However, not only microporous active carbon of high surface area but also mesoporous carbon black of lower surface area (216 m /g) can serve as an excellent support for Pt—Cu catalyst in the addition of trichlorosilane to alkenes as well as of polyhydrosiloxanes of allyl chloride and 1-octene to produce silicone waxes, with a long alkyl chain (>C8) (123). Platinum catalyst (0.5%) supported on porous (acidic) AI2O3 is very attractive in the industrially important hydrosilylation of cyclopentene and cyclohexene (130). 

Cyclopentenone Synthesis. When activated with Lewis acid catalysts or silver ion, 1-phenylthio-l-trimethylsilylethylene reacts with a,/3-unsaturated acid chlorides at a low temperature in CH2Cl2. The cation intermediates undergo a silicon-directed Nazarov cyclization to give 3-phenylthio-substituted cyclopentenone derivatives (eq 3). The phenylthio moiety at the /3-position of cyclopentenones can be effectively utilized for the introduction of an alkyl substituent by addition/elimination. 

It is of interest to note that in several instances the effect of a catalyst such as aluminum chloride or boron fluoride is enhanced by the presence of an acidic assistant. Alkylation by olefins with aluminum chloride as a catalyst is favored by the presence of anhydrous hydrogen chloride, and the condensation of primary alcohols with benzene uting boron fluoride is possible only with the aid of an. assistant such as phosr phoric anhydride, benzenesulfonic acid, or sulfuric acid. It has been foimd also that chlorides of tin, silicon, or titanium increase the catalytic activity of aluminum chloride, whereas ferric chloride decreases the... 

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