# Advances in Organic and Organic-Inorganic Hybrid Polymeric Supports for Catalytic Applications
## 2 Organocatalysed Non-Asymmetric Reactions
### Synthesis of Cyclic Carbonates
Bis-imidazolium salts with different organic linkers (ethane, butane, octane, \(p\)-xylene) between the two imidazolium units and two types of halides as counterions (X = Br or I) were used. Since the materials were synthesized using an excess of bis-imidazolium salts with respect to the SH groups of thiol-functionalized silica, a cross-linked oligomeric network of imidazolium units on the silica support was obtained. The catalytic activity of materials **18**, **19a-b**, **20a-b**, **21a-b** was valued and compared in the coupling reaction between CO\({}_{2}\), under supercritical conditions, and two different epoxides, an aliphatic terminal epoxide (1,2-epoxyhexane) and an aromatic terminal epoxide (styrene oxide). With all catalysts, higher epoxide conversions were observed with styrene oxide as compared to 1,2-epoxy-hexane. The materials **20b** and **21b**, having octane and \(p\)-xylene as linker, respectively, and iodide as counterion, were identified as the most active catalysts. These results indicated that the leaving ability of the halide played a role in determining the reaction rate and that a better separation between the imidazolium units, obtained with the linker with the longest chain (octane), could prove favourable for simultaneous reaction at both of them. The results with these new catalysts were markedly superior compared to the previous optimum mlc-SILP catalyst (SiO\({}_{2}\)-\(p\)-xylene-Br) [20]. Material **20b** was also employed in the synthesis of cyclic carbonates from different epoxides and CO\({}_{2}\). In this case, higher carbonate yields were observed with the terminal epoxides, while cyclohexene oxide and cyclopentene oxide showed lower reactivity, leading to only low carbonate yields. Recently, a new type of stable highly cross-linked cationic polymer microspheres, denoted as **22**, was solvothermally synthesized from the reaction of 1,2,4,5-tetrakis(bromomethyl)benzene and 4,4\({}^{\prime}\)-bipyridine (Scheme 10) [21]. Various solvents, including THF, toluene, acetonitrile, and ethyl acetate were applied. The spherical particles **22** (with sizes of approximately 2-3 nm) formed in THF were the most stable and exhibited high activity and selectivity in the coupling reaction between CO\({}_{2}\) and different substituted epoxides at 120 \({}^{\circ}\)C under metal-free and solvent-free conditions. In addition, spherical particles **22**, insoluble in the reaction system, had good recyclability, which was mainly attributed to the cross-linked covalent cationic structure. After the reaction, the cross-linked cationic polymer microspheres **22** could be easily recycled by filtration or centrifugation and reused six successive times without a significant decrease in the efficiency or structural deterioration. Among ionic liquids used as catalysts for the cycloaddition of CO\({}_{2}\), the quaternary phosphonium-based ionic liquids have not been extensively studied due to their less tailored structures, limited heterogenizing method and required harsh reaction conditions. In 2014, phosphonium-based ionic liquids functionalized with hydroxyl and carboxyl groups showed good catalytic activity in the synthesis of cyclic carbonates in the absence of co-catalyst and solvent [22]. In light of the superiority of the functionalized phosphonium-based ionic liquids, recently polymer nanoparticles grafted with hydroxyl-functionalized phosphonium-based ionic liquid **24** were prepared by radical copolymerization of diphenyl(\(p\)-vinylphenyl)(3-hydroxypropyl)-phosphonium bromide (**23**) with ethylene glycol dimethylacrylate (EGDMA) (Scheme 11) [23]. Under optimized conditions, the cross-linked polymer **24** exhibited good catalytic activity in the coupling reaction between CO\({}_{2}\) and various terminal epoxides (yield 90.0%-97.3%). Cyclohexene oxide gave relatively low activity (46.8%), due to large steric hindrance.