title: Activation of aryl and heteroaryl halides by an iron(I) complex generated in the reduction of [Fe(acac)₃] by PhMgBr: electron transfer versus oxidative addition.
abstract: The mechanism of the reactions of aryl/heteroaryl halides with aryl Grignard reagents catalyzed by [Fe(III)(acac)3] (acac=acetylacetonate) has been investigated. It is shown that in the presence of excess PhMgBr, [Fe(III)(acac)3] affords two reduced complexes: [PhFe(II)(acac)(thf)n] (n=1 or 2) (characterized by (1)H NMR and cyclic voltammetry) and [PhFe(I)(acac)(thf)](-) (characterized by cyclic voltammetry, (1)H NMR, EPR and DFT). Whereas [PhFe(II)(acac)(thf)n] does not react with any of the investigated aryl or heteroaryl halides, the Fe(I) complex [PhFe(I)(acac)(thf)](-) reacts with ArX (Ar=Ph, 4-tolyl; X=I, Br) through an inner-sphere monoelectronic reduction (promoted by halogen bonding) to afford the corresponding arene ArH together with the Grignard homocoupling product PhPh. In contrast, [PhFe(I)(acac)(thf)](-) reacts with a heteroaryl chloride (2-chloropyridine) to afford the cross-coupling product (2-phenylpyridine) through an oxidative addition/reductive elimination sequence. The mechanism of the reaction of [PhFe(I)(acac)(thf)](-) with the aryl and heteroaryl halides has been explored on the basis of DFT calculations.
authors.affiliation: Ecole Normale Supérieure, Département de Chimie, UMR CNRS-ENS-UPMC 8640, 24 Rue Lhomond, 75231 Paris Cedex 5 (France), Fax: (+33) 1-4432-2502; Department of Chemistry, The University of British Columbia, Vancouver, British Columbia, V6T 1Z1 (Canada). glefevre@chem.ubc.ca.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Lefèvre
authors.forename: Anny
authors.initials: A
authors.lastname: Jutand
keywords: Grignard reaction; electron transfer; iron; oxidative addition; redox chemistry