Synthesis of gel-type imino-amino functionalized methacrylate-styrene terpolymers as supports for palladium catalysts for the Suzuki–Miyaura reaction

Gel-type polymers uploaded with 8.5–15.4 wt% of palladium(II) ions based on the low cross-linked glycidyl methacrylate resins with imino-amino functionalities coupled with heterocyclic rings were prepared, characterized (FT-IR, DR UV–vis, HR-SEM, ICP-OES methods) and tested as catalysts in the Suzuki–Miyaura reactions of a series bromo- and chloroarenes with phenylboronic acid at 25–70 °C. The effects of the reaction medium, temperature, catalyst structure and concentration on the activity of the catalysts and Pd leaching were studied for the model reaction of bromobenzene with phenyl boronic acids. It was found that the catalysts with the branched system of TAEA were more active than those with the linear one (EDA). The activity of the catalysts strongly depended on the nature of heteroatoms of heterocyclic aldehyde moieties in imine ligands. The catalyst activity decreased in the order: 2-pyridinecarboxaldehyde (PA) > furfural (FA) > 2-thiophenecarboxaldehyde (TA). The best of the catalysts was used additionally in the reactions of substituted bromo- and chloroarenes. It turned out to catalyze efficiently the cross-coupling of bromoarenes bearing both electron donor and electron acceptor substituents. The reactivity of bromoarenes changed in the order: CHO > H∼F > Me > OMe ≫ OH. The catalyst was found inactive in coupling of 4-nitrochlorobenzene under the same reaction conditions. The catalyst with TAEA moieties was recycled in the reaction of bromobenzene minimum five times. Its activity, however, decreased gradually on each stage.

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► Novel recyclable Pd catalysts for Suzuki–Miyaura reaction under mild conditions.
► Imino-amino functionalized methacrylate-styrene gels as supports for Pd catalysts.
► Pd(II) ion loading as a factor in determining the activity of polymer catalysts.
► An advantageous effect of branching ligand systems on the activity of Pd catalysts.