In the past couple of decades there has been a strong interest in the organic community to switch from precious metal catalysts like palladium to iron, as it is abundant, low-cost, sustainable, non-toxic, and provides opportunities for novel reactivity. Unlike palladium-catalyzed reactions, the mechanisms of iron-catalyzed reactions are not well studied. Using a combination of spectroscopy, synthesis, and low-temperature crystallization we are able to elucidate these mechanisms at the molecular level. Not only does this provide insight into the current reaction but it also will inform the development of new reactions going forward. N,N,N’,N’-tetramethylethylenediamine (TMEDA) is one of the most widely used additives in iron-catalyzed cross coupling, however, the molecular-level role during catalysis is highly debated in the literature. Studies have focused on C(sp2)-C(sp3) Kumada cross-coupling with mesityl Grignard reagent as the model nucleophile, where either a TMEDA-bound iron complex or a homoleptic iron-ate complex was proposed to be selectively generating cross-coupled product. In recently published work, the role of TMEDA in iron-catalyzed C(sp2)-C(sp3) cross-coupling reactions is explored focusing on relevant Grignard reagents (i.e. phenyl and ethyl) and effective protocols (i.e. slow nucleophile addition), revealing that TMEDA-iron(II)-aryl intermediates are part of an iron(II)/(III)/(I) reaction study where radical recombination with FePhBr(TMEDA) results in selective product formation with high yields.

TMEDA-iron adduct reaction manifold in iron-catalyzed C(sp2)-C(sp3) cross-coupling reactions

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