# Advances in Organic and Organic-Inorganic Hybrid Polymeric Supports for Catalytic Applications
## 4 Metal-Catalysed Non-Asymmetric Reactions
### C-C Coupling Reactions
Material **137** was employed in 0.1 mol % in Heck reaction between syrenes or methyl acrylate and various aryl iodides in DMF/H\({}_{2}\)O 4:1 in the presence of TEA at 90 \({}^{\circ}\)C, showing good results. Under these conditions, catalyst **137** released Pd species in solution and the leached Pd species  
Figure 49: Polystyrene-supported Cu(II) complex **136** as catalyst for Sonogashira reaction. catalysed the reaction. Adding a six-fold amount of the imidazolium-based support **21a**, they were very efficiently scavenged. The new supported Pd species (0.5-0.6 wt %) were not catalytically active. The non-catalytic activity of low loaded Pd material was explained assuming that such Pd species were strongly bound into the inner surface of the multilayered structure of support **21a**. The use of the highly cross-linked imidazolium-based materials as palladium scavengers was also extended [82]. A novel and highly sustainable protocol for flow Heck reaction in presence of the catalyst **138**, constituted by palladium (10 wt %) supported on cross-linked imidazolium network, was reported (Scheme 51) [83]. Flow reactors and protocols were defined in order to optimize the recovery and reuse of the catalyst, minimize waste and in particular, the amount of organic solvent needed to isolate the final products. The flow protocol was defined by charging a mixture of the catalyst **138** (0.1 mol %) and the supported base, diethylaminomethyl-polystirene (PS-TEA) (1.5 equiv. ), in a stainless steel HPLC column, while the reactants solution was charged in another glass column, acting as the reservoir. After setting the temperature at 130 \({}^{\circ}\)C, the reaction mixture was cyclically pumped through the columns at a 2.0 mL/min flow rate for the time required to obtain quantitative conversion. Reusability of catalyst **138** was investigated in Heck reaction to methyl cinnamate. The reuse of the catalyst was repeated for four consecutive runs, achieving a TON of about 4000 and a TOF of about 0.08 s\({}^{-1}\). No apparent activity loss was observed and a Pd content of about 4 ppm was found in the products obtained after each cycle of the flow protocol. Furthermore, the CH\({}_{3}\)CN aqueous azeotrope used in the reaction was distilled off and recovered with a high purity (GLC analysis), totally comparable to the starting azeotropic mixture, thus being reusable without affecting the reaction yield. The flow procedure at 130 \({}^{\circ}\)C was extended to the reactions between two aryl iodide and styrene or methyl acrylate, obtaining good yields (76%-97%) and Pd content into the products <5 ppm. The combination of the flow technique and sustainable reaction conditions led to a substantial reduction of the waste production, as proved by the low E-factor value of 12. Taking advantage of application of highly cross-linked imidazolium-based materials as supports for palladium nanoparticles, another approach for the palladium immobilization, based on the highly loaded thiazolite-functionalized silica support **49**, was described (Scheme 21) [84]. The thiazolite-based support **49** was treated with an aqueous solution of Na\({}_{2}\)PdCl\({}_{4}\) and successively with sodium borohydride, to afford the catalyst **139** (Scheme 52). Catalyst **139** in 0.1 mol % loading was used in the Suzuki-Miyaura reaction between phenylboronic acid or 4-formylphenylboronic acid and a set of aryl bromides (or iodides) in ethanol/water at 50 \({}^{\circ}\)C in the presence of K\({}_{2}\)CO\({}_{3}\) as base. Biphenyl compounds were obtained in high yields (58%-99%). The catalyst was also used in the Heckreaction between aryl iodides and methyl acrylate or styrene. Good to excellent yields were obtained, except in the reaction between 2-iodothiophene and methyl acrylate. The recyclability was studied in Suzuki reaction. The catalyst was used three times without loss of catalytic activity.