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.

Chemistry (Weinheim an der Bergstrasse, Germany)

PubMedID: 24596072

Lefèvre G, Jutand A. 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. Chemistry. 2014;.
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.