Construction Of Catalytic Active Centers In Functionalized Organic Macromolecule For Green Catalysis

With the increasing attention of the global energy and environmental issues, as well as the deepening of the concept of green chemistry,efficient and recyclable catalyst and green catalytic process has become the frontier and hot research in the field of international catalysis. Based on the unique solubility of functionalized organic macromolecule, as well as its role in the regulation of catalytic active center, we constructed the catalytic active center in organic macromolecule through covalent/non-covalent method to realize the heterogenization of homogeneous catalyst, and also the development of a new system of catalytic oxidation reaction based on green oxidant.(1) Keggin-type phosphotungstic acid(HPW) was successfully incorporated into the PAMAM matrix with different generation through ionic interactions and hydrogen bonds, resulting in novel dendritic phosphotungstate hybrids(dendri-PW hybrids). The dendritic PAMAM matrix as a countercation not only fine-tunes the redox properties of the PW anions but also has a positive “dendrimer effect” on the enhancement of the catalytic activity of the hybrids. Efficient performance was observed over the dendri-PW hybrids in the selective oxidation of alcohols with H2O2. Furthermore, the dendritic ammonium cations impartreactioncontrolled phase-transfer function to the dendri-PW hybrids. The catalysts precipitated from the solvent upon consumption of H2O2 and could be reused several times without loss of activity and selectivity.(2) Chiral salen Ti(IV) complex was successfully grafted on the ionic liquid decorated PAMAM dendrimer periphery through covalent linkage.Dense packing of the chiral salen Ti(IV) complex at the periphery benefited for the formation of a catalytically active dimeric titanium complex [{(salen)Ti(μ-O)}2], resulting in the enhanced catalytic activity due to cooperative effect. Furthermore, the ionic liquid moiety provided an unique ionic environment in favor of stabilizing the active intermediate. The catalyst thus exhibited excellent catalytic efficiency in asymmetric oxidation of sulfide with H2O2(30 wt%) as oxidant. In addition, the selective solubility of PAMAM dendrimer made the catalysts selectively dissolve in organic solvents. The catalysts could be facily separated from the reaction system by simply controlling the solvents, resulting in efficient reuse.(3) An series of chiral salen Mn(III) polymers with build-in phase transfer capability was prepared by bridging the chiral salen Mn(III) units with polyethylene glycol(PEG)-based di-imidazolium ionic liquid(IL)side by side by covalently-polymerization. Amphipathic nature of PEG-based di-imidazolium IL moiety allowed the obtained catalysts to undergo inherentphase transfer catalysis in asymmetric epoxidation ofunfunctionalized olefins with NaClO, which in turn increased the reaction rate of epoxidation in water–dichloromethane biphasic system. High activity and entioselectivity were observed over the novel catalysts than those over neat complex. Furthermore, the efficient phase transfer catalysts could be easily recovered by solvent precipitation and be recycled for several times without significant loss of the activity and enantioselectivity.