Role of TMEDA in Iron-Catalyzed Coupling Reactions

Abstract

Significance: Iron-catalyzed cross-coupling reactions are an active area of research due to the non-toxicity of iron relative to other commonly used transition metals. However, an understanding of the mechanistic processes underlying these reactions is still unclear. In the present paper, the authors study the effect of TMEDA on the crosscoupling reactions of ArMgX with alkyl halides. Based on X-ray structures of tetrahedral complexes 1 and 2 and radical clock experiments, the authors have proposed a possible catalytic cycle for this reaction.Comment: This is an excellent study providing new mechanistic insight into these coupling reactions in addition to the "ate" mechanism already proposed by Fürstner. Radical clock experiments with 1-bromo-5-hexene and bromomethylcyclopropane suggest that one-electron oxidation of Fe(II) to Fe(III) occurs in the reaction with RBr with a lifetime that allows for partial ring opening of the cyclopropylmethyl radical. Hopefully, this study will allow for more purposeful and informed design of more efficient ligand-catalyst systems for ironcatalyzed cross-coupling reactions.