# Advances in Organic and Organic-Inorganic Hybrid Polymeric Supports for Catalytic Applications
## 4 Metal-Catalysed Non-Asymmetric Reactions
### C-C Coupling Reactions
New polymer supports for palladium catalysts were prepared by immobilization of poly(amidoamine) PAMAM type hyperbranched systems on an epoxy-functionalized polymer(GMA resin) derived from terpolymers of glycidyl methacrylate, styrene, and divinylbenzene [85]. The supported PAMAM **141** and **142** were synthesized considering two methods (Scheme 53). The first included the immobilization of the zeroth order PAMAM dendrimer **140**[86] on the GMA resin. The second relied on multi-stage chemical modification of the GMA resin in turn with tris(2-aminoethyl)-amine (TAEA), methyl acrylate and ethylenediamineime (EDA). Palladium(II) ions were immobilized onto supported PAMAM **141** and **142** thus obtaining the catalysts **141-Pd** and **142-Pd** with Pd(II) loading of 16.3 and 8.1% Pd(II) ions, respectively. Polymer-supported Pd(II) complexes **141-Pd** and **142-Pd** were tested as catalysts in the Suzuki-Miyaura reaction. Kinetic plots obtainedfor the reaction of bromobenzene with phenylboronic acid performed in the presence of **141-Pd** and **142-Pd**, in i-PrOH-H\({}_{2}\)O mixture, at 70 \({}^{\circ}\)C, using KOH as base and 0.5 mol % of catalyst, showed that **141-Pd** was more active than **142-Pd**. Therefore, **141-Pd** was used for the further catalytic studies with a series aryl bromides and phenylboronic acid obtaining high conversions (90%-100%). An incomplete conversion (about 90%) was noted only in the case of _p_-bromophenyl. The recyclability of catalyst **141-Pd** was studied in the reaction of _p_-bromoanisole with phenylboronic acid. The catalyst beads were reused nine times without regeneration. Despite, the loading of palladium diminished in about 9% after 5 th run and about 12.5% after 10 th run, the efficiency of **141-Pd** was not influenced. Recently, polyamidoamine dendrimers (PAMAM) were also immobilized onto single-walled carbon nanotubes (SWCNTs) to obtain suitable supports for palladium nanoparticles [87]. In detail, hybrid supports SWCNT-PAMAM **144a** and **144b** were prepared by direct reaction between pristine SWCNTs and cystamin-based PAMAM dendrimers 2.5 G **143a** and 3.0 G **143b**, respectively (Scheme 54). Then, heterogeneous catalysts **144a-Pd** and **144b-Pd** were obtained by treatment of **144a** and **144b** with [PdCl4]2- and successive reduction with sodium borohydride, respectively. By this strategy, materials **144a** and **144b** were uniformly decorated with small palladium nanoparticles with mean diameters of 3.2 and 1.6 nm, respectively, in 10 wt % loading of Pd. Both catalysts were tested in Suzuki-Miyaura and Mizoroki-Heck reactions and catalyst **144b-Pd** showed the best performances. The authors proposed a \"release and catch\" mechanism [88] for both reactions. During the Suzuki reaction, the re-deposition of soluble Pd-species was highly effective. During the Heck coupling instead, part of the soluble Pd species was stabilized by both the base and the solvent and subsequently leached away. The reusability of nanocatalyst **144b-Pd** was also studied. It was shown to be recyclable at least four times in the Suzuki reaction and six times in the Heck coupling with quantitative yields. A novel strategy for the preparation of highly efficient Pd-based heterogeneous catalyst, using a porous organic polymer containing phenanthroline ligands, was reported [89]. Particularly, catalyst **147** was obtained by metalation with Pd(OAc)\({}_{2}\) of polymer organic **146** synthesized through the copolymerization of divinylbenzene and vinyl-functionalized phenanthroline monomer **145** under solvothermal conditions (Scheme 55). The activity of catalyst **147** was tested in Suzuki, Heck and Sonogashira reactions. The Suzuki coupling between phenylboronic acid and aryl bromides or aryl iodides at 80 \({}^{\circ}\)C gave biphenyl products with excellent yields (94%-99%).