화학공학소재연구정보센터
Macromolecules, Vol.31, No.22, 7581-7587, 1998
Synthesis and characterization of a polymer-supported salen ligand for enantioselective epoxidation
We report the synthesis of a covalently linked salen complex onto the surface of a 98 vol % styrene/2 vol % divinylbenzene polymeric support. The solid-phase method allows manipulation of the substituents on the salen complex in a more versatile manner than can be done for the homogeneous ligand and the production of a support for catalysis that guarantees accessibility to the supported active sites. The ligand was constructed in a stagewise manner that allows the possibility for combinatorial syntheses. Immobilized salen complex 1 was formed by the sequential treatment of the resin with 2,4,6-trihydroxybenzaldehyde, a chiral trans-1,2-diaminocyclohexane, and 3,5-di-tert-butylsalicylaldehyde. After loading the immobilized ligand with Mn, the support effected the enantioselective epoxidation of 1,2-dihydronaphthalene, cis-beta-methylstyrene, and styrene as test olefins with enantiomeric excesses of 46%, 79% (cis-epoxide), and 9%, respectively, using aqueous sodium hypochlorite as the oxidant. The heterogeneous catalyst also showed a selectivity toward the formation of the trans-epoxide in the case of cis-beta-methylstyrene. The heterogeneous system allows ease of separation and recycle, albeit with diminished enantioselectivity in reuse.