A Sustainable Buchwald-Hartwig C–N Coupling for Arylamine Synthesis with Heterogeneous Catalysis of Iron Oxide Nanoparticles

We report an efficient and sustainable synthetic method for arylamines using iron oxide nanoparticles (γ-Fe₂O₃ NPs) as a heterogeneous catalyst for the C–N coupling of aryl bromides and arylamines. Through optimization, we achieved a 93% yield at 160 °C, finding that 4 equivalents of LiBr were essential for suppressing the homocoupling byproducts. The γ-Fe₂O₃ NPs demonstrated superior selectivity compared to several homogeneous iron catalysts. A significant advantage of this system is the selective mono-amination of a dibromide (84% yield), a challenging reaction for palladium catalysts, because of the two-fold coupling of the side reaction. The ferromagnetic catalyst was easily recovered and reused for four cycles with high catalytic activity. Mechanistic studies using TEMPO suggest the reaction proceeds via a radical pathway.