Engineering And Catalysis Studies On Functional Polyoxometalate-based Metal-organic Frameworks

Metal-organic frameworks (MOFs), with large surface area, well-ordered porous structures and tailorable functionality, have shown great promise in heterogeneous asymmetrically catalytic conversions, since they not only can impose size and shape selective restriction through readily fine-tuned channels or pores, but also can be tailored by judicious combinations of the building blocks for specific application. Polyoxometalates (POMs) are well-known catalysts studied in the olefin epoxidation with high proton acid property, false liquid phase behavior and excellent thermal and oxidative stability toward oxygen donors. The introduction of POMs into these hierarchicral MOFs at the molecular level possibly increases the stability and corresponding functions, providing a promising way to combine the organic and inorganic catalytic components synergistically.This thesis mainly concerns on the construction and catalysis studies of POMOFs. The main contents are as follows:1) A series of crystalline materials constructed by PW12O403-, Zn2+and Ln3+(Ln=Eu, Yb, Er), and dpdo with diversity structures from1D to3D POMOFs through hydrothermal reaction and first were explored in the hydrolysis of phosphodiester bond cleavage. These POMOFs greatly accelerated the cleavage rate of BNPP, with the pseudo-first-order rate constant in the range of10-7～10-6s-1, which were comparable with that of homogeneous system.2) By incorporating an oxidation catalyst [BW12O40]5-a nd a chiral group, L or D-PYI, into one single framework, two enantiomorphs Ni-PYI1and Ni-PYI2were obtained via self-assembly, respectively. The coexistence of both the chiral directors and the oxidants within a confined space provided a special environment for the formation of reaction intermediates in a stereoselective fashion with high yeild (>75%) and high selectivity (95%ee). They are the first example of chiral POMOFs as the heterogeneous synergy catalysts in asymmetric catalytic reactions.3) By incorporating an oxidation catalyst H3PW12O40and a chiral group, L or D-PYI, into one single framework, two enantiomorphs Cu-PYI1and Cu-PYI2were obtained via self-assembly, respectively. They acted as multifunctional catalysts for olefin oxidations, aldol reaction, and cyanosilylations.4) By incorporating an oxidation catalyst [ZnW12040]6-, a chiral group, L or D-PYI, and a3-amino-4,4’-bipyridine (NH2-BPY) into one single framework. Two nbo topology enantiomorphs Zn-NH2-PYI1and Zn-NH2-PYI2were achieved with a high density of well-oriented Lewis acid and basic sites, the chiral directors and the oxidation catalysts. The coexistence of both the chiral directors and the oxidants within a confined space provided a special environment for the formation of reaction intermediates in an enantioselectivity fashion with high selectivity. The synergy of both the Lewis acid and the Lewis basic were desirable for high catalytic activity for the chemical fixation of CO2into cyclic carbonates at mild reaction conditions. These POMOFs as the heterogeneous synergistic catalyst realized the cascade enantioselectivity transformation of styrene to cyclic carbonates by one-pot reaction with about90%yield and about85%ee.