ASYMMETRIC CATALYST DERIVED FROM POLYMER IMOBILIZED CHIRAL 1,2-DIAMINES

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Starting from benzoin derivative we have synthesized new chiral 1,2-diamine having two phenolic hydroxyl groups. This chiral 1,2-diamine was attached to chloromethylated polystyrene. Chiral monomers having 1,2-diamine structure were also prepared and polymerized with styrene and other achiral monomers to give the polymer-supported chiral 1,2-diamine. We have synthesized various kinds of chiral 1,2-diamine monomers. A 1,2-diamine monomer having two p-vinylbenzyl groups as polymerizable group gave the crosslinked polymer. A 1,2-diamine monomer having one p-vinylbenzyl group was polymerized with styrene to give a linear soluble polymer. In the presence of cross-linking agent the insoluble polymer having chiral 1,2-diamine pendant was obtained. Dendritic monomer structure was also introduced and polymerized.In order to evaluate the performance of the polymeric chiral 1,2-diamine ligands, we chose asymmetric hydrogenation of ketone as a model reaction. Chiral complex of 1,2-diamine-BINAP-Ru … More Cl_2 developed by Noyori et al is a powerful tool to obtain optically active secondary alcohols in high level of enantioselectivity. We have prepared the same complex using polymer-supported chiral 1,2-diamine mentioned above. The asymmetric hydrogenation is usually performed in 2-propanol to give the alcohol in quantitative conversion with high enantioselectivity. Unfortunately, no reaction occurred with the polystyrene based polymeric chiral 1,2-diamine ligand mainly due to its shrinkage in the solvent. We found that the mixed solvent of DMF and 2-propanol allowed the hydrogenation using polymeric chiral ligand to give the alcohol. Polymeric catalyst derived from cross-linked polymer having 1,2-diamine pendant showed the best performance in the hydrogenation of ketones. Enantioselectivities attained with this type of polymeric catalyst are almost same as those from the low-molecular-weight catalyst in homogeneous solution system. The insoluble polymeric catalysts could be easily separated from the reaction mixture and recycled many times without loss of catalytic activity. Less