# Advances in Organic and Organic-Inorganic Hybrid Polymeric Supports for Catalytic Applications
## 5 Metal-Catalysed Asymmetric Reactions  
Supported metal-based catalysts can be also used in asymmetric transformations. In this section, two examples of metal-catalysed asymmetric C-C forming reactions, including the allylation of ketones and the Henry reaction, and three examples of asymmetric hydrogenation are described. Synthesis of the supported 1,1-binaphthol (BINOL) ligand **169** and its application in the titanium-catalysed asymmetric allylation of ketones were reported [104]. Supported BINOL ligand **169** was prepared by anchoring the enantiopure 6-ethynyl-BINOL **168** to an azidomethylpolystyrene resin through a copper-catalysed alkyne-azide cycloaddition reaction (Scheme 63). The enantiopure 6-ethynyl-BINOL **168**, having a suitable alkyne anchoring linker, was synthesized by the following route. The selective monoesterification of the hydroxyl groups of (_R_)-1,1-binaphthol (**163**) with bulky pivaloyl chloride was performed, to allow the successive chemoselective bromination at the 6-position and thus avoid the 6,6\({}^{\prime}\)-difunctionalization of the naphthyl groups. The obtained bromide derivative **165** was treated with pivaloyl chloride, and subsequently with trimethylsilylacetylene to introduce the trimethylsilylethynyl substituent, by a palladium-catalysed Sonogashira coupling reaction, and thus to furnish intermediate **167**. Finally, the hydrolysis and desilylation of latter intermediate by treatment with K2 CO3 in methanol afforded the enantiopure 6-ethynyl-BINOL **168**. The supported BINOL ligand **169** was employed in the asymmetric allylation of a series of ketones with tetraallytin under optimized conditions in presence of titanium(IV) isopropoxide and 2-propanol in CH2 Cl2. The polystyrene (PS)-supported BINOL ligand **169** was converted into its  
Figure 62: Preparation of polystyrene-linked tris(triazolyl)methanecopper (I) cationic catalyst **162** and its application in carbene transfer reaction in batch and flow conditions. diisopropyloposyt titanium derivative in situ and the asymmetric allylation mediated by the so-formed PS-supported (BINOLate)Ti species led to alcohols with high yield (67%-96%) and enantiomeric excesses (70%-95%). Recycling of the PS-supported (BINOLate)Ti species was investigated through the asymmetric allylation of 3-methylacetophenone. The catalyst was recovered by filtration and reused. A decrease in enantioselectivity was observed. It was established by ICP-MS analysis that up to 96% of its initial titanium content is leached from the resin in a single reaction cycle. Based on these results, the intercycle remetallation with titanium tetraisopropoxidewas carried out to obtain the effective reuse. By using this approach, both yield and enantioselectivity were essentially preserved after three consecutive reaction cycles. Supported BINOL ligand **169** was also employed in the tandem asymmetric allylation/epoxidation of (_E_)-2-benzylidenecyclohexanone and the tandem asymmetric allylation/Pauson-Khand reaction of 1-(2-(phenylethylynyl)phenyl)ethanoneone, obtaining final products with high stereoselectivity in both cases. Several kinds of polytopic chiral ligands based on the bis(oxazoline) and azabis(oxazoline) motifs were used in the preparation of coordination polymers having copper as the ligand connecting metal [105]. Particularly, the ditopic ligands **170a-c** bearing _tert_-butyl, phenyl and indanyl substituents, respectively, the different ditopic ligand **171** bearing triazole units in the linker, the tritopic **172** and tetratopic **173** ligands were used (Scheme 64). The coordination polymers, formed by mixing the corresponding polytopic ligand (**170**-**173**) and Cu(OAc)\({}_{2}\) in the appropriate Cu/Ligand molar ratio, were tested as recoverable catalytic systems for the Henry reaction of \(o\)-anisaldehyde with nitromethane or nitroethane. During the reactions, the polymers disassembled due to competitive coordination of either the reactants or the reaction solvent.