Friedel–Crafts alkylation of benzene with (polychloromethyl)silanes

(Polychloromethyl)silanes (Cl3−mMemSiCH3−nCln: m=0–3; n=2, 3) reacted with excess benzene in the presence of aluminum chloride to give (polyphenylmethyl)silanes. Such reactions occurred at the temperatures ranging from room temperature (m=2, 3; n=2) to 80°C (m=0, 1; n=2, 3), indicating that the reactivity increases with increasing the number (m) of electron-donating methyl-group(s) at the silicon. In particular, (dichloromethyl)silanes with two or three methyl groups at the silicon (m=2 or 3; n=2) underwent the alkylation and the decomposition of their products at room temperature. The reaction with (dichloromethyl)trimethylsilane occurred immediately at room temperature to give no (diphenylmethyl)trimethylsilane, but diphenylmethane and trimethylchlorosilane via the decomposition of alkylation product. (Trichloromethyl)silanes (m=0, 1; n=3) reacted with excess benzene to give (triphenylmethyl)silanes as major products and the unusual (diphenylmethyl)silanes as minor. It was found that unusual (diphenylmethyl)silanes were formed by the decomposition of (triphenylmethyl)silanes under the reaction condition. In the alkylation to benzene, the reactivity of (polychloromethyl)silanes (Cl3−mMemSiCH3−nCln: m=0–3; n=2, 3) decreases in the following order: m=3>2>1>0; n=3>2.