Green recyclable resin-supported sulfur ionic liquid for efficient CO₂ cycloaddition to cyclic carbonates

The efficient conversion of CO₂ into cyclic carbonates constitutes a significant research direction in green chemistry. While researchers have long focused on developing heterogeneous catalytic systems to advance this process, the construction of such systems that are highly active, easily recyclable, halogen-free, and co-catalyst-free remains challenging. To address this challenge, a straightforward amidation strategy was employed to construct a resin-supported sulfur-containing ionic liquid catalyst. Specifically, 6-mercaptonicotinic acid was anchored onto Rink Amide resin (RAR) via a glycine linker, and the thiol group on the nicotinic acid moiety formed an ion pair with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), resulting in the heterogeneous catalyst RAR-G-S^-·DBUH⁺. Detailed characterization by elemental analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy mapping confirmed the successful synthesis and structural integrity of the catalyst, with an active site loading of 0.444 mmol/g. Remarkably, RAR-G-S^-·DBUH ⁺ exhibited excellent performance in the cycloaddition of CO₂ with various terminal epoxides, achieving near-quantitative yields (up to 99%) under optimized conditions. Its practical applicability was further demonstrated in gram-scale reactions, maintaining yields above 93%. Moreover, the catalyst displayed a unique switching ability in the reaction pathway when applied to challenging N-aryl-substituted epoxides with low selectivity: by modulating the electronic nature of the substituents, the product selectivity could be precisely controlled to favor either cyclic carbonates or oxazolidinones. This work provides an efficient, stable, and easily separable heterogeneous catalytic system for CO₂ utilization, showing promising potential for industrial application.