Cobalt(III) Halide Metal-Organic Frameworks Drive Catalytic Halogen Exchange

The selective halogenation of complex (hetero)aromatic systems is a critical yet challenging transformation relevant to medicinal chemistry, agriculture, and biomedical imaging. However, current methods are limited by toxic reagents, ex-pensive homogeneous second- and third-row transition metal catalysts, and/or poor substrate tolerance. Herein, we demonstrate that porous metal–organic frameworks (MOFs) containing terminal Co(III) halide sites represent a rare and general class of heterogeneous catalysts for the controlled installation of chlorine and fluorine centers into electron-deficient (hetero)aryl bromides using simple metal halide salts. Mechanistic studies support that these halogen exchange (halex) reactions proceed via redox-neutral nucleophilic aromatic substitution (SNAr) at the Co(III) sites. The MOF-based halex catalysts are recyclable, enable scalable halogenation with minimal waste generation, and facilitate halex in contin-uous flow. Our findings represent the first example of SNAr catalysis using MOFs, expanding the lexicon of synthetic trans-formations enabled by these materials.