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

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 MoO* 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.