Nonheme iron catalyst mimics heme-dependent haloperoxidase for efficient bromination and oxidation

Abstract

The [Fe]/H₂O₂ oxidation system has found wide applications in chemistry and biology. Halogenation with this [Fe]/H₂O₂ oxidation protocol and halide (X⁻) in the biological system is well established with the identification of heme-iron–dependent haloperoxidases. However, mimicking such halogenation process is rarely explored for practical use in organic synthesis. Here, we report the development of a nonheme iron catalyst that mimics the heme-iron–dependent haloperoxidases to catalyze the generation of HOBr from H₂O₂/Br⁻ with high efficiency. We discovered that a tridentate terpyridine (TPY) ligand designed for Fenton chemistry was optimal for FeBr₃ to form a stable nonheme iron catalyst [Fe(TPY)Br₃], which catalyzed arene bromination, Hunsdiecker-type decarboxylative bromination, bromolactonization, and oxidation of sulfides and thiols. Mechanistic studies revealed that Fenton chemistry ([Fe]/H₂O₂) might operate to generate hydroxyl radical (HO^•), which oxidize bromide ion [Br⁻] into reactive HOBr. This nonheme iron catalyst represents a biomimetic model for heme-iron–dependent haloperoxidases with potential applications in organic synthesis, drug discovery, and biology.