Light-Driven Iron Catalysis: A Strategy for Heteroarene Borylation

Abstract

Transition-metal-catalyzed C–H borylation is a powerful strategy for constructing C–B bonds, which are valuable intermediates in organic synthesis. However, many existing methods require precious metal catalysts, harsh conditions, or stoichiometric oxidants, and often demand strict exclusion of moisture and oxygen, limiting their practicality. Herein, we report a mild method for direct C(sp²)–H borylation of (hetero)arenes and perfluoroarenes using air as a green oxidant. The approach employs inexpensive FeCl₃ as a photocatalyst and chlorine radicals as hydrogen atom transfer (HAT) reagents. The transformation is driven by chlorine radicals generated via ligand-to-metal charge transfer (LMCT), which abstract hydrogen atoms from B–H bonds to form boryl radicals, thereby enabling subsequent C–B bond formation. Using only catalytic amounts of FeCl₃ and air as a green terminal oxidant, this strategy overcomes the limitations previously associated with oxygen radical mediated B–H activation. A key advantage of our protocol is its remarkable robustness under ambient conditions, requiring neither anhydrous solvents nor inert-atmosphere protection. Only a catalytic amount of FeCl₃ is needed, with air serving as the sole stoichiometric oxidant to regenerate the active iron species, thereby rendering the overall process atom-economical and waste-minimizing. The synthetic utility of this method was demonstrated by the successful preparation of a broad spectrum of (hetero)aryl and perfluoroaryl boronates bearing diverse functional groups. Furthermore, a one-pot, two-step Suzuki–Miyaura cross-coupling of perfluoroarenes was accomplished without intermediate isolation, affording biaryl products in good overall yields. This tandem procedure highlights the considerable industrial potential of our strategy for the sustainable synthesis of pharmaceuticals, agrochemicals, and advanced functional materials.