Effect of the substituents at the silicon of (omega-chloroalkyl)silanes onthe alkylation to benzene

(omega-Chloroalkyl)silanes [Cl3-mMemSi(CH2)(n)-Cl: m = 0-3, n = 1-3] underw ent Friedel-Crafts alkylation with benzene in the presence of aluminum chlo ride to give alkylated products. Such alkylation reactions took place at te mperatures ranging from room temperature (m=0-1, n =2, 3; m = 3, n= 1) to 8 0 (m = 1, 2; n := 1) and 200 degrees C (m =0; n = 1), depending on the subs tituent(s) of the silicon and the alkylene-chain s:pacer between the silico n and C-CI bond of (omega-chloroalkyl)silanes. In the alkylation to benzene , the reactivities of (omega-chloroalkyl)silanes increase as the number (m) of methyl-group(s) at the silicon and the alkylene length between the sili con and C-CI bond increases. While decomposition of alkylation products was observed at two more methyl groups substituted at silicon in the cases of (chloromethyl)silanes such as (chloromethyl)dimethylchlorosilane and (chlor omethyl)trimethylsilane. The reaction with (chloromethyl)trimethylsilane oc curred at room temperature to give trimethylchlorosilane, toluene and xylen e via a decomposition reaction of the products. No (trimethylsilylmethyI)be nzene was formed. In the alkylation to benzene, the reactivity of (omega-ch loroalkyl)silanes decreases in the following order: m = 3 > 2 > 1 > 0; n=3> 2 much greater than 1. The results are consistent with the stability of the carbocation generated by the complexation of (omega-chloroalkyl)silanes wi th aluminum chloride. (C) 2000 Elsevier Science S.A. All rights reserved.