A crown ether–functionalized natural asphalt derivative as a support for palladium immobilization: An efficient heterogeneous catalyst for Suzuki–Miyaura biaryl synthesis

ABSTRACT In this study, a novel heterogeneous palladium catalyst based on natural asphalt was designed and synthesized via stepwise construction of a 1-aza-15-crown-5 ether ligand followed by selective immobilization of palladium species. The synthetic route involved sonobromination of natural asphalt, subsequent functionalization with diethanolamine through reaction with alkyl bromide sites, and its sequential S N 2 and ring-closure reactions with 1,2-dichloroethane and dichloroethane to generate the aza-crown ether framework, which served as a multidentate coordination site for Pd incorporation. The resulting natural asphalt supported 1-aza-15-crown-5 ether-Pd catalyst was thoroughly characterized and evaluated in the Suzuki–Miyaura cross-coupling reaction of various aryl halides with phenylboronic acid using ethanol as a green solvent. The catalyst exhibited excellent activity, affording biaryl products in high yields (81–97%) within short reaction times (10–180 min). The catalyst demonstrated good stability and recyclability, maintaining its performance over at least five consecutive cycles with negligible loss of activity (from 94% in the first cycle to 91% in the fifth cycle). Furthermore, hot filtration and ICP-OES analyses confirmed the heterogeneous nature of the catalyst with minimal palladium leaching. The combination of a low-cost natural carbon support, well-defined ligand environment, high efficiency, and green reaction conditions highlights the potential of this system as a practical and sustainable platform for C–C bond formation.