Selective Decarbonylative Bromination of Aromatic Aldehydes Enabled by Ensemble-Engineered Au–Pd Alloy Nanoparticle Catalysts

Bromoarenes are important structural motifs across a wide range of chemical fields and serve as versatile synthetic intermediates. However, the direct synthesis of bromoarenes from ubiquitous and readily available aldehydes has remained challenging. Herein, we report the decarbonylative bromination of aldehydes catalyzed by supported Au–Pd alloy nanoparticles using simple bromoarenes as bromine-transfer reagents. A broad range of aromatic aldehydes bearing diverse functional groups underwent selective bromination under directing group-free and acid- or base-free conditions. Mechanistic studies combining catalyst characterization, control experiments, and kinetic analyses revealed that alloying with Au(0) species diluted contiguous Pd ensembles, thereby suppressing the CO extrusion step in the competing intramolecular decarbonylation pathway and favoring the intermolecular bromination. In addition, the weak acid–base properties of the hydroxyapatite support inhibited competing Ullmann coupling and aldehyde decomposition pathways. These synergistic ensemble and support effects enabled the highly selective bromination of aldehydes.