# Advances in Organic and Organic-Inorganic Hybrid Polymeric Supports for Catalytic Applications
## 4 Metal-Catalysed Non-Asymmetric Reactions
### Epoxidation of Alkenes
A new process, which employed polybenzimidazole-supported Mo(VI) complex **119** as catalyst for epoxidation of cyclododecene and dodecene with TBHP as oxidant, was investigated (Scheme 42) [71]. The polymer-supported Mo(VI) complex **119** was prepared through ligand exchange procedure carried out in presence of polybenzimidazole and an excess of molybdenum acetylacetonate relative to polymer bound ligands under reflux in toluene. The catalytic activity of **119** was studied under different reaction conditions in a batch reactor. The optimum reaction conditions for epoxidation of both cyclododecene and dodecene were found at 80 \({}^{\circ}\)C, 0.3 mol % Mo catalyst loading and 2.5:1 feed molar ratio of alkene to TBHP. About 98% yield of 1,2-epoxycyclododecane and about 79% yield of 1,2-epoxydodecane were obtained at 350 min. The leaching of any catalytically active Mo species from the polymer-supported catalyst **119** was investigated by supernatant studies. The results of supernatant studies of cyclododecene epoxidation revealed that catalytically active Mo species were leached from the polymer matrix, especially at the first three consecutive reactions, causing a decrease of conversion from 96% to 31%. No evidence of Mo leaching was showed for dodecene epoxidation. The authors suggested that the leaching of Mo species from catalyst **119** might be due to the release of Mo species contained in the microgels as a result of mechanical attrition of the polymer catalyst beads. However, they also suggested that this effect would be absent in continuous epoxidation process using a reactive distillation column, as the catalyst would be firmly packed inside a fixed column. [PERSON] et al. described application of two covalent metalloporphyinic polymers (CMPs) based on the azo (-N=N-) linkage, as catalysts for epoxidation of alkenes [72]. These materials, denoted as azo-CMP-**120** and azo-CMP-**121**, were obtained by reaction between manganese _meso_-tetra (4-nitro-phenyl)porphyrin and _p_-phenylenediamine or benzidine respectively, in DMF at 150 \({}^{\circ}\)C in the presence of potassium hydroxide under N\({}_{2}\) atmosphere (Scheme 43). Activity of catalysts was compared in epoxidation of styrene with TBHP in acetonitrile at 70 \({}^{\circ}\)C. The catalyst azo-CMP-**120** displayed a better performance than azo-CMP-**121**. Styrene oxide was obtained with yields of 82% and 69% with azo-CMP-**120** and azo-CMP-**121** respectively. The catalyst azo-CMP-**120** was also employed in epoxidation of other olefins showing high yields with cyclic olefin (79%-100%) and lower yields with linear olefin (35%-58%). Low yield was obtained in reaction with _trans_-stilbene (31%). The catalyst azo-CMP-**120** was recycled five times with a slight decrease in catalytic activity. Recently, Mn(III)salophen supported on nanosilica triazine dendrimer **124** was synthesized and used as new nanocatalyst for epoxidation of different alkenes with NaIO\({}_{4}\) (Scheme 44) [73]. **Scheme 43. ** Metalloporphyinic polymers azo-CMP-**120** and azo-CMP-**121** as catalysts for the epoxidation of alkenes. **Scheme 44. ** Preparation of Mn(III)salophen supported on nanosilica triazine dendrimer **124** and its catalytic activity in the epoxidation of alkenes. Catalyst **124** was prepared by coordination reaction of nano-silica-supported triazine dendritic polymer (G2) **123** with Mn(salophen)Cl. Polymer **123** was previously synthesized starting from a propylamine-functionalized nano-silica by using an iterative method that included the nucleophilic substitution reaction between the chloride groups of cyanuric chloride and amino groups of nano-silica followed by reaction with bis(3-aminopropyl)amine [74]. The optimization of epoxidation reaction conditions was studied and several alkenes were oxidized to their corresponding epoxides in good to excellent yield (52%-95%) in CH\({}_{3}\)CN/H\({}_{2}\)O at room temperature with 4 mol % of catalyst **124**. The reusability of **124** was studied in the epoxidation of cyclootene.