Radical-Friedel–Crafts benzylation of arenes over a metallic–basic bifunctional MoO2 surface

Abstract

Selective ether bond activation is essential in organic synthesis and natural polymer depolymerization. Herein, we report that MoO₂ with negligible acidity but characterized metallic–basic bifunctional properties can efficiently catalyze the benzylation of arenes with benzyl ethers as a benzylation reagent via a radical-Friedel–Crafts mechanism. Through combining catalyst characterizations, control experiments, thermomechanical analysis, intermediates capture, and density functional theory (DFT) calculations, multiple Mo sites on the MoO₂ surface facilitate the initial transfer of oxygen-centered groups from adsorbed dibenzyl ether (DBE*). This process involved the homolytic cleavage of Bn–OBn ether bonds, promoted by adjacent-group auxiliary activation of benzyl aromatic rings adsorbed on the MoO₂ surface. The generated benzyl radical (Bn˙) attacks the aromatic ring of the arene substrates, while the first-exfoliated oxygen-centered group (BnO*) and its potential decomposition fragment, the oxidative MoO* species, abstract a H atom from the above addition-intermediate to restore aromaticity and achieve benzylation. The remaining alcohol (BnOH) can also participate in the benzylation mediated by MoO₂. This study could provide some inspiration on C–O bond activation and ether utilization mediated by a Mo-based catalyst.