Ruthenium Complexes Immobilized on Functionalized Knitted Hypercrosslinked Polymers as Efficient and Recyclable Catalysts for Organic Transformations

A hypercrosslinked polymer (HCP)-immobilized ruthenium catalyst (HCP–PPh3–Ru) was prepared from benzene and triphenylphosphine (PPh3) through a one-step external cross-linking reaction. The structure and composition of the catalyst were fully characterized by many physicochemical methods. HCP–PPh3–Ru was found to possess high Brunauer–Emmett–Teller (BET) surface area, large pore volume, and low skeletal density. Moreover, the Ru catalyst was also featured some advantages, such as low synthetic cost and good chemical and thermal stability. HCP–PPh3–Ru was then used as a recoverable and effective catalyst for the synthesis of 2,4-diaryl-substituted pyridines from acetophenones, ammonium acetate (NH4OAc) and dimethylformamide (DMF), and the cycloaddition reaction of diazodicarbonyl compounds with olefins to afford dihydrofurans. In addition, a combination of HCP–PPh3–Ru and Amberlyst-15 enabled us to establish a simple protocol for the direct synthesis of carbazole derivatives from diazodicarbonyl compound, alkyl vinyl ether and indole. In these selected reactions, the catalyst was easily recovered and reused several times without significant activity loss.