Palladium clusters on dicarboxyl-functional hypercrosslinked porous polymers for oxidative homocoupling of benzene with O₂

Aerobic oxidative homocoupling of benzene with dioxygen (O₂) is one of the promising routes for the synthesis of important chemical intermediate biphenyl. In the most cases, high valent palladium (Pd) species are regarded as the active sites, while metallic stage Pd° species are inactive. Herein, we presented the fabrication of highly dispersive Pd clusters with the average size of 1.2 nm on a dicarboxylic acid-functional hypercrosslinked polymer (HCP) with large pore volume and high surface area, which was directly synthesized through the copolymerization of phthalic acid and biphenyl via Bronsted acid-catalyzed Friedel-Crafts alkylation. Catalyst behaved excellent catalytic activity in converting benzene into biphenyl via oxidative homocoupling with O₂, exhibiting a high yield up to 18 % plus a record turnover number and turnover frequency as larger as 505 and 253 h⁻¹, respectively. Such catalytic behavior is mainly attributed to the formation of ultrafine Pd clusters promoted by the surface dicarboxyl functional groups.