Heterogenization of Palladium Trimer and Nanoparticles Through Polymerization Boosted Catalytic Efficiencies in Recyclable Coupling and Reduction Reactions

The development of heterogeneous palladium catalysts has shown continuous vitality in the field of catalysis and materials. In this work, we report one concise free radical polymerization approach to accomplish the aromatic palladium trimer functionalized polymers PSS_y-[Pd₃]⁺ (2) and its derived palladium nanoparticles (3). Full characterizations could confirm the successful combination of cationic [Pd₃]⁺ or nanoparticles with poly(p-sulfonated styrene) skeleton. Compared to their monomeric tri-palladium precursor (1) and common Pd(dba)₂, Pd(PPh₃)₄, Pd(OAc)₂, heterogeneous PSS_y-[Pd₃]⁺ (2) shows much superior catalytic activities (0.15 mol %, TOF=1333.3 h^-1) in the SMCC reaction. The identically ligated PdNPs (3) are formed in-suit in the presence of NaBH₄ and accomplish quantitative reduction of 4-nitrophenol in just 320 s (0.50 mol %, TOF=2250 h^-1). Moreover, these heterogeneous catalysts are reused for 5-6 times without significant loss of catalytic activity. Their superior catalytic ability is probably attributed to the synergistic effect of polymer entanglement and the tri-palladium fragment. This work enlightens that the immobilization of palladium clusters or nanoparticles by polymerization could offer multiple advantages in stability, efficiency and recyclability for their involved catalyses and show far-reaching future implications.