Synergistic Cu–OH and zeolite confinement in Cu/MCM-22 for benzaldehyde-mediated Mukaiyama epoxidation of long-chain α-olefins

The Mukaiyama epoxidation of olefins, leveraging molecular oxygen and aldehydes to generate epoxides, is a cornerstone of sustainable synthesis but is hindered by compromising epoxide selectivity and aldehyde coupling efficiency due to the high reactivity of acylperoxy radicals. Here, we report a Cu/MCM-22 catalyst that synergistically integrates Cu-OH active sites with zeolite confinement to achieve exceptional selectivity and efficiency in the aerobic epoxidation of long-chain linear α-olefins. Comprehensive characterization, including transmission electron microscopy, X-ray absorption spectroscopy and Fourier-transform infrared spectroscopy, confirms atomically dispersed Cu²⁺ ions within MCM-22's framework, enabling benzaldehyde activation via Cu²⁺/Cu⁺ redox cycling and H₂O formation. Electron paramagnetic resonance and density functional theory (DFT) studies reveal that the confined pores of MCM-22 stabilize acylperoxy radicals, suppressing undesired pathways and promoting epoxide formation. Catalytic evaluations demonstrate 97% conversion and 90% selectivity for 1-undecene epoxidation, which was further improved to 99% selectivity by deactivating the Cu sites on the zeolite external surface, resulting in a roughly 3-fold increase in aldehyde coupling efficiency and significantly outperforming unconfined Cu/Al₂O₃ and Cu/SiO₂. Kinetic analyses and DFT calculations highlight reduced energy barriers (84 kJ·mol^-1) for benzaldehyde activation and enhanced chemoselectivity driven by zeolite confinement. This work elucidates the pivotal role of tailored active sites and spatial constraints in radical catalysis for selective epoxide synthesis.