# Advances in Organic and Organic-Inorganic Hybrid Polymeric Supports for Catalytic Applications
## 5 Metal-Catalysed Asymmetric Reactions
The resulting soluble monomeric metal complexes acted as true homogeneous catalysts. At the end of each reaction, the release-capture strategy for the recovery and reuse of enantioselective catalysts, based on the precipitation of an insoluble coordination polymer, was shown to be effective in all cases. In the reaction between \(o\)-anisaldehyde and nitromethane,the best performances were obtained with ditopic ligand **171. ** The use of the complex **171**-Cu(OAc)\({}_{2}\) provided excellent results in both yield and enantioselectivity (96% and 91% respectively). It was reused up to 12 runs without loss of enantioselectivity and activity. In the reaction between _o_-anisaldehyde and nitroethane, the best performances were obtained with ligand **170c**. The **170c**-Cu(OAc)\({}_{2}\) could be reused up to 14 runs with a slight decrease in yield, diastere- or enantioselectivity. A new approach of fabricating core-shell structured solid catalysts for the asymmetric transfer hydrogenation (ATH) of aromatic ketones with [Cp*RhCl\({}_{2}\)]\({}_{2}\) (Cp* = pentamethylcyclopentadiene) as metal precursor was investigated [106]. In detail, the hybrid core-shell nanospheres **176** with \(N\)-(_para_-toluenesulfonyl)-1,2-diphenylethylenediamine-polystyrene (TsDPEN-PS) in the core and poly(methyl acrylate)-functionalized silica in the shell were fabricated by two synthetic steps (Scheme 65). In the first step, TsDPEN-PS latex nanoparticles **175** were prepared through the emulsion polymerization of a mixture of chiral monomer **174** and styrene. In the second step (the coating process), the hydrolysis and condensation of the mixture of tetraethoxysilane and poly(methyl acrylate)-functionalized alkoxysilyl (PMA-organosilane), in presence of TsDPEN-PS latex nanoparticles **175** and cetyltrimethylammonium bromide (CTAB) as a structure-directing agent, were carried out. The hybrid core-shell nanospheres **176** with different compositions and surface properties were tested in the Rh-catalysed ATH of acetophenone in aqueous HCOONa. The core-shell structured solid catalyst **177** was generated in situ by reaction between the hybrid core-shell nanospheres **176** and [Cp*RhCl2]2 (Cp* = pentamethylcyclopentadiene). The studies showed that the presence of CTAB and poly(methyl acrylate) polymer in the shell favoured high activity, which was mainly due to the increased surface hydrophobicity. Furthermore, the hybrid core-shell nanospheres **176**, obtained by using 10 mol % of the chiral monomer, in the process of the formation of the core, and 10 mol % of PMA-organosilane, in process of the formation of shell, were employed in the Rh-catalysed ATH of a wide range of simple aromatic ketones obtaining high enantioselectivity (ee: 73%-99%). The catalyst was seperated through filtration and was recycled. Recycling study was carried out by ATH of acetophenone. After each run, the reaction time was prolonged to maintain the catalytic activity but the ee value of each run kept up well. The gradual decrease in the catalytic activity was due to the slight loss of Rh, which was confirmed by inductively coupled plasma analysis (5.4% in total Rh loading). Recently, the modular solid-phase synthesis of a library of 16 supported phosphine-phosphite (P-OP) ligands, denoted as **181a-r**, and its application in rhodium catalysed asymmetric hydrogenation were reported (Scheme 66) [107]. Variations in structure of supported phosphine-phosphite (P-OP) ligands **181a-r** were generated by using phosphines bearing different substituents (R1), cyclic sulfates having a varying backbone length (n) and different substituents (R2) and by employing various chlorophosphites. The starting synths of the solid-phase synthesis were supported phosphine-boranes **178a-b**, synthesized starting from Merrifield resin and primary lithium phosphides having different substituents (R1). Upon deprotonation of **178a-b** with lithium diisopropylamide (LDA), the lithiated phosphine-boranes reacted with a cyclic sulphate, affording compounds **179a-h**.