The hydrosilylation of cyclic alkenes and linear alkenes with trialkylsilanes in the presence of Lewis acid catalysts under mild conditions gave the corresponding (trialkylsilyl)alkanes in fair to good yields. The reaction of 1-methylcyclohexene with triethylsilane at −20 °C gave cis-1-triethylsilyl-2-methylcyclohexane with regio- and stereoselectivity via a trans hydrosilylation pathway. Cycloalkenes having an alkyl group at the double-bonded carbon showed better reactivity than nonsubstituted compounds in the Lewis acid-catalyzed hydrosilylation. The catalytic reactivity of Lewis acids decreases in the following order:  AlBr3 > AlCl3 > HfCl4 > EtAlCl2 > ZrCl4 > TiCl4. When triorganochlorosilane was used as an activator in the aluminum chloride-catalyzed reaction, the hydrosilylation rate drastically increased. The results are consistent with a stepwise mechanism proceeding via the formation of a trialkylsilylenium ion intermediate.

Friedel-Crafts alkylations of ferrocene, 1, with allylchlorosilanes in the presence of Lewis acid catalysts under mild conditions gave regiospecific [1-methyl-2-(alkylchlorosilyl)ethyl]ferrocenes in fair to good yields depending upon the substituents on silicon, along with small amounts of dialkylated products. The alkylation of ferrocene with 1.2 equiv of (2-methylallyl)dimethylchlorosilane, 2b, at 0 °C gave monoalkylated ferrocene 3b and an isomeric mixture of dialkylated products in 76% and 4% yields, respectively. The yield of the dialkylated ferrocene mixture increased to 21% when 2 equiv of alkylating agent 2b was used. The two components of the dialkylated product mixture were identified as 1,1′-dialkylated ferrocene 4b (17%), and 1,3-dialkylated ferrocene 4b′ (4%). A higher yield of the 1,1′-diadduct compared to the 1,3-diadduct indicates that the electron-donating alkylsilyl group does not greatly enhance a second alkylation on the same ring. The reactivities of allylchlorosilanes in the ferrocene alkylations decrease in the following order: allyldialkylchlorosilane > allyl(alkyl)dichlorosilane . allyldichlorosilane ≈ allyltrichlorosilane. The catalytic efficiencies of Lewis acids for the alkylations decrease in the following order: HfCl 4 > ZrCl 4 > AlCl 3 > AlBr 3 >TiCl 4 .

Friedel−Crafts alkylation reactions of biphenyl with (dichloroalkyl)chlorosilanes [Cl3 - m Me m Si(C n H2 n - 1Cl2), m = 0−2, n = 1−3] at temperatures ranging from 120 to 160 °C in the presence of a Lewis acid catalyst gave cyclized products, fluorenyl-substituted chlorosilanes, in 47−94% yields. In these reactions, the reactivities of (dichloroalkyl)silanes generally increase as the number of methyl groups on the silicon atom and the alkyl chain length increase. However, desilylation of the alkylated products and starting chlorosilanes was observed in the case of (dichloroalkyl)silanes having two or more methyl groups on the silicon. Alkylation with (dichloromethyl)dimethylchlorosilane proceeded at 120 °C but gave fluorene and dimethyldichlorosilane resulting from desilylation of the products. The reactivities of (dichloroalkyl)silanes decrease in the following order:  m = 2 > 1 > 0; n = 2 > 1. The catalytic efficiencies of Lewis acids for the cycloalkylation reactions decrease in the following order:  AlCl3 > AlBr3 > HfCl4 > ZrCl4 ≫ TiCl4.