Palladium immobilized on lignin-based hypercrosslinked polymers as robust and efficient heterogeneous catalyst for Suzuki-Miyaura reactions in water

Lignin is an important organic polymer and a potential renewable resource. In this work, two novel palladium immobilized on lignin-based hypercrosslinked polymers were successfully fabricated via the Friedel-Crafts alkylation reaction and metallization. The protocol is associated with mild conditions, low cost, high yield, easy separation. The structure of the catalysts were studied by FT-IR, N2 sorption, XPS, ICP, TGA, TEM, and SEM. Analysis indicates that the polymers exhibit significant characteristics such as large pore volume, highly distributed palladium, excellent chemical and thermal stability, and high specific surface areas. Subsequently, the heterogeneous catalysts were deployed within the context of the Suzuki-Miyaura reaction as a means to evaluate their catalytic activity. In the realm of aqueous environments, HCP-L&Pd-I showcases remarkable efficiency in catalyzing the Suzuki-Miyaura reaction, which benefited from the synergistic effect between the hierarchical pore structure in the material and numerous hydroxyl groups in lignin coordinating with palladium. Under optimum conditions, 0.1 mol% Pd content was enough to react with 97 % yield of biphenyl. Moreover, the catalyst was simply regenerated and reused six times without significant activity loss. This protocol perhaps provides a new perspective on the effective preparation of biphenyl aromatic compounds utilizing lignin-based heterogeneous catalysts in the Suzuki-Miyaura reaction.