TMEDA in iron-catalyzed Kumada coupling: amine adduct versus homoleptic "ate" complex formation

Robin B Bedford; Peter B Brenner; Emma Carter; Paul M Cogswell; Mairi F Haddow; Jeremy N Harvey; Damien M Murphy; Joshua Nunn; Christopher H Woodall

doi:10.1002/anie.201308395

TMEDA in iron-catalyzed Kumada coupling: amine adduct versus homoleptic "ate" complex formation

Angew Chem Int Ed Engl. 2014 Feb 10;53(7):1804-8. doi: 10.1002/anie.201308395. Epub 2014 Jan 21.

Authors

Robin B Bedford¹, Peter B Brenner, Emma Carter, Paul M Cogswell, Mairi F Haddow, Jeremy N Harvey, Damien M Murphy, Joshua Nunn, Christopher H Woodall

Affiliation

¹ School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS (UK). r.bedford@bristol.ac.uk.

PMID: 24505000
DOI: 10.1002/anie.201308395

Abstract

The reactions of iron chlorides with mesityl Grignard reagents and tetramethylethylenediamine (TMEDA) under catalytically relevant conditions tend to yield the homoleptic "ate" complex [Fe(mes)3 ](-) (mes=mesityl) rather than adducts of the diamine, and it is this ate complex that accounts for the catalytic activity. Both [Fe(mes)3 ](-) and the related complex [Fe(Bn)3 ](-) (Bn=benzyl) react faster with representative electrophiles than the equivalent neutral [FeR2 (TMEDA)] complexes. Fe(I) species are observed under catalytically relevant conditions with both benzyl and smaller aryl Grignard reagents. The X-ray structures of [Fe(Bn)3 ](-) and [Fe(Bn)4 ](-) were determined; [Fe(Bn)4 ](-) is the first homoleptic σ-hydrocarbyl Fe(III) complex that has been structurally characterized.

Keywords: Grignard reagents; catalysis; cross-coupling; iron.