# Advances in Organic and Organic-Inorganic Hybrid Polymeric Supports for Catalytic Applications
## 2 Organocatalysed Non-Asymmetric Reactions
### Synthesis of Cyclic Carbonates
The catalytic activity was comparable to that of homogeneous catalyst **23** (99.5% of propylene carbonate) and was higher than homopolymers synthesized using **23** and EGDMA as monomers. Besides, **24** exhibited superior catalytic performance than polymer nanoparticles synthesized by copolymerization of triphenylpropylphosphonium bromide with EGDMA, showing the important role of hydroxyl groups. The catalyst had a good thermal stability and excellent reusability up to six cycles without any significant loss of activity. Figure 10: Synthesis of poly(ionic liquid) **22** and its application in the formation of cyclic carbonates. Most immobilized organocatalyst systems for the conversion of epoxides to cyclic carbonates, require operating temperatures above 100 \({}^{\circ}\)C, which challenges their overall sustainability. The following example reports a recyclable catalyst system that promotes the conversion of CO2 under mild conditions. The bifunctional catalyst **25**, where the triazolium and pyrogallol units were linked to distinct positions along the polymer backbone, was prepared starting from azidomethyl polystyrene and tested as catalyst in coupling reaction between CO2 and 1,2-epoxyhexane at 45 \({}^{\circ}\)C (Scheme 12) [24]. **Scheme 12. Preparation of bifunctional resin **25** and its use as catalyst in the synthesis of cyclic carbonates. This bifunctional resin **25** maintained its activity level for a longer period than binary catalyst system **26** and the one-component bifunctional catalyst **27**. An appreciable reduction in activity only started to occur after five runs, but a regenerative treatment with methyl iodide permitted the recovery of catalytic activity; for example, the resin **25** was used in 11 consecutive runs giving a total of 938 turnovers/1,2,3-trihydroxybenzene unit which was significantly higher than those that might be obtained with **26** or **27**. The bifunctional catalyst **25** was employed in the synthesis of other cyclic carbonates. High yields were obtained with terminal epoxides and low yields with internal epoxides. Among internal epoxides, only conversion of indene oxide proceeded smoothly (yield > 99%). A new class of nanoporous polymers incorporating sterically-confined \(N\)-heterocyclic carbenes (NP-NHCs), as heterogeneous nanoporous organocatalysts for the conversion of CO\({}_{2}\) into cyclic carbonates at atmospheric pressure, was reported [25]. Particularly, the nanoporous polymer NP-NHC **33** was prepared following the synthetic strategy depicted in Scheme 13. **Scheme 13. Preparation of NHC-nanoporous polymer **33** and its application in the synthesis of cyclic carbonates. At first, a tetrahedral core based on tetraphenyl methane incorporating 2,6-disopropyl aniline moieties at the terminal positions, denoted as **30**, was synthesized by reaction between tetrakis(4-bromophenylyl)methane (**28**) and borane **29**. After, three synthetic steps led to the polymer **33**: (a) copolymerization of **30** with glyoxal in order to obtain the polymer **31**; (b) reaction with paraformaldehyde in the presence of HCl to form **32** having the corresponding imidazolium chloride moieties and (c) generation of sterically-confined \(N\)-heterocyclic carbenes **33** by neutralization of the imidazolium chloride moieties with potassium _tert_-butoxide in THF. The catalytic activity of the NP-NHC polymer **33** was tested in the conversion of CO\({}_{2}\) into cyclic carbonates under atmospheric pressure of CO\({}_{2}\) (0.1 MPa) at 120 \({}^{\circ}\)C with 5 wt % catalyst loading. Excellent yields (92%-98%) and 100% product selectivity were obtained with mono aliphatic substituted terminal epoxides. Traces or no conversion for the phenyl and benzyl substituted epoxides were observed. According to the authors, this could be due to the molecular sieving property of polymer **33**, conferred by the pore diameter of polymer (~0.4 nm), which was less than that of kinetic diameter of the aromatic epoxides.