Exploring fundamental reactions relevant to iron-catalyzed cross-coupling: strong-field CNC ligands enable two-electron chemistry

For a variety of organometallic catalytic processes, most notably Suzuki-Miyaura cross coupling reactions, the oxidative addition of aryl and alkyl halides is a key substrate activation step. Demonstration of this fundamental transformation with iron has little precedent, principally due to competing atom-abstraction chemistry. The aryl-substituted bis(imidazol-2-ylidene)pyridine iron dinitrogen complex, (3,5-Me₂^MesCNC)Fe(N₂)₂ (3,5-Me₂^MesCNC = 2,6-(2,4,6-Me-C₆H₂-imidazol-2-ylidene)₂-3,5-Me₂-pyridine) reacts rapidly with non-coordinating aryl and alkyl halides (R–X) at room temperature to yield the corresponding oxidative addition products, (3,5-Me₂^MesCNC)Fe(R)(X)(N₂), in good yields (70 – 80%). Mechanistic studies, specifically relative rate studies, stereochemical probes, and radical clocks, are consistent with a concerted oxidative addition pathway for aryl halides and a radical pathway for alkyl halides. Further reactivity of the (3,5-Me₂^MesCNC)Fe(R)(X)(N₂) products such as transmetalation and C–C bond forming reductive elimination will also be discussed.