A six-membered N-heterocyclic polyionic liquids with palladium nanoparticles as a heterogeneous catalyst for the multicomponent one-pot reaction of carbon dioxide.

A series of heterogeneous catalysts, designated as POP-n-Pd (where n = 1, 2, 3, or 4), were synthesized by polymerizing a six-membered N-heterocyclic compound with an alkyl substituted group monomer (S1), using divinylbenzene (DVB) as crosslinkers. This process was followed by the incorporation of palladium (Pd) nanoparticles. The impact of the substituted group and the S1:DVB ratio in the catalysts, together with the reaction conditions, was investigated to assess their influence on the catalytic performance in converting propylamine, carbon dioxide (CO) and 4-iodoanisole to oxazolidinones. The POP-1-Pd catalyst, featuring a methyl substituted group and a S1:DVB ratio of 1:4, exhibited remarkable efficiency, resulting in an excellent yield of 96 % under room temperature and ambient pressure conditions. Furthermore, it has demonstrated wide applicability across a variety of substrates and in the treatment of lime kiln exhaust gas. Additionally, POP-1-Pd can be used in a gram-scale reaction and maintains its performance after six recycles, with no significant decline in yield. The possible catalytic mechanism is proposed as follows: the catalyst's pores adsorb both CO and substrates, creating a high concentration reactant enrichment microenvironment. This facilitates the activation of both CO and substrates by the imidazole moiety and Pd nanoparticles in the catalyst, thereby generating oxazolidinones.