Iron catalysis in the reaction of grignard reagents with alkyl halides

Abstract

The stoichiometry and kinetics of the reaction between various Grignard reagents and alkyl halides with an iron catalyst have been examined in tetrahydrofuran solutions. The catalytic iron species is produced in situ by the reduction of iron-(II) and -(III) halides by Grignard reagent. The activity of the catalyst is dependent on the solvent and deactivation by ageing is attributed to aggregation of the catalytic iron species. The catalytic process is postulated to occur via a redox cycle, in which the oxidative addition of alkyl halide to a reduced form of iron is followed by disproportionation of the alkyliron intermediates to regenerate the iron catalyst. Alkyl radicals are formed in the step involving oxidative addition. Thus, styrenepreferentially scavenges only that alkyl moiety derived from the alkyl halide. Side reactions involving the catalytic exchange of Grignard reagent with alkene and alkyl halide are also described.