Immobilization, as a methodology to effectively recover and reuse asymmetric catalysts, has attracted the interest of many research groups resulting in a large number of catalysts being subjected to investigation.[1] Multicomponent asymmetric catalysts, [2,3] composed of plural ligands, metals, and functional moieties, have proved to be challenging systems in this regard ( Figure 1). Multicomponent asymmetric catalysts function like enzymes in facilitating a wide range of regioand stereoselective reactions that make use of the synergistic cooperation between the active sites; it is important to maintain the structural motif during immobilization if high reactivities are to be realized. The conventional approach, which involves the random introduction of ligand and functional units onto a sterically irregular polymer backbone, resulted in less effective catalysts. Multidentate ligands with attached sites for metals at the opposite sides in the molecular skeleton readily form insoluble metal-bridged polymers (Figure 2). If chiral metal-bridged regions on the generated polymer function as asymmetric catalysts, a simple and efficient approach for the immobilization of multicomponent asymmetric catalysts without the need for a polymer support would be realized. While metal-organic coordination networks, including metal-bridged polymers, have been utilized for catalytic asymmetric reactions, the enantioselectivity of the products obtained has been very low. [4]
Immobilization, as a methodology to effectively recover and reuse asymmetric catalysts, has attracted the interest of many research groups resulting in a large number of catalysts being subjected to investigation.[1] Multicomponent asymmetric catalysts, [2,3] composed of plural ligands, metals, and functional moieties, have proved to be challenging systems in this regard ( Figure 1). Multicomponent asymmetric catalysts function like enzymes in facilitating a wide range of regioand stereoselective reactions that make use of the synergistic cooperation between the active sites; it is important to maintain the structural motif during immobilization if high reactivities are to be realized. The conventional approach, which involves the random introduction of ligand and functional units onto a sterically irregular polymer backbone, resulted in less effective catalysts. Multidentate ligands with attached sites for metals at the opposite sides in the molecular skeleton readily form insoluble metal-bridged polymers (Figure 2). If chiral metal-bridged regions on the generated polymer function as asymmetric catalysts, a simple and efficient approach for the immobilization of multicomponent asymmetric catalysts without the need for a polymer support would be realized. While metal-organic coordination networks, including metal-bridged polymers, have been utilized for catalytic asymmetric reactions, the enantioselectivity of the products obtained has been very low. [4]
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