Size and stability modulation of Pd nanoparticles on porous hypercrosslinked ionic polymer for heterogeneous aerobic oxidative coupling of diaryl ether

Oxidative coupling of two aromatic C–H bonds is normally catalyzed by Pd(II) species involving an electrophilic attacking step. Herein, we demonstrated surprisingly the high activity of heterogeneous Pd(0) nanoparticles (NPs) in catalyzing the intramolecular oxidative coupling of diaryl ether with O₂. The Pd(0) NPs with different average particle sizes were constructed by using the supports of ionic hypercrosslinked porous polymers that were straightforwardly synthesized through the copolymerization of 2,3-pyridinedicarboxylic anhydride and biphenyl in a chlorosulfonic acid-catalyzed route. In the case of moderate ionic moiety content, the constructed Pd(0) NPs were highly active in the coupling of diphenylether to dibenzofuran, affording a high yield of 72 % associated with a large turnover number of 91 that exceeded 18-folds of homogeneous palladium acetate. Kinetic analysis and radical quenching results demonstrate a carbon radical related catalytic pathway. Following the same methodology, various other diaryl ether with electro-donating and electro-withdrawing groups were converted into the corresponding dibenzofuran derivatives.