| POM-based organic-inorganic hybrid materials combine POMs and functional organic ligands through various chemical bonds at nanoscale level,taking advantages of both components.Such materials give rise to many potential applications in the fields of organic catalysis,nonlinear optics,nanomaterials and anti-virus activity.The design synthesis and characterization of those materials have considerably attentions.This study utilizing POMs and chiral organic ligands as the building block constructes two kinds of chiral POM-based organic-inorganic hybrid materials.1.Monolacunary Keggin-type anions(XW11O39n-,x=P and W)have higher charges,hence increased basicity and nucleophilicity than their parent complete species.Thus they react quite easily with electrophilic organosilone derivative PICS in water or in non-aqueous solvents,leading to the isolation of new optically pure chiral PICS-grafted POMshybrid molecules:[?C4H9?4N]H2{PW11O39O[3,5-ditertbutylphenolimino-?1R,2R?-cyclohexyl-2-amino-propylsilyl]2}·4CH3CN?I1?[?C4H9?4N]H2{PW11O39O[3,5-ditertbutylphenolimino-?1S,2S?-cyclohexyl-2-amino-propylsilyl]2}·4CH3CN?I2?[?C4H9?4N]2H2{SiW11O39O[3,5-ditertbutylphenolimino-?1R,2R?-cyclohexyl-2-amino-propylsilyl]2}·4CH3CN?I3?[?C4H9?4N]2H2{SiW11O39O[3,5-ditertbutylphenolimino-?1S,2S?-cyclohexyl-2-amino-propylsilyl]2}·4CH3CN?I4?IR,31P and 29Si NMR,ESI-MS spectroscopy confirm that two chemical equal organic silicon groups are bonded to the surface of the lacunary XW11O39n+.The asymmetric catalytic study of compound I1-I4 are investigated with aldol reaction,showing excellent selectivities.The ee value and dr value of commpoud I3is 98%and 95:5.In addition,the reusability of catalyst I3 is stable after 8 times of cycles.2.Immobilization on MNPs,chiral organosilone derivative R-PICS electrostatic interacting with keggin-type anionsh as obtained hybrid materials MNP-?R-PICS?-POM?II?.The asymmetric catalytic properties of hybrid materials II are investigated with aldol reaction.The hybrid materials with a 1:1 stoichiometry of R-PICS-POMare better than those with the corresponding 1:2 catalyst.The activity sequence is MNP-?R-PICS?-SiW12?II2?>MNP-?R-PICS?-PW12?II1?>MNP-?R-PICS?-PMo12?II3?.The ee value and dr value of hybrid material II2 is 86%and 80:20.With the loss of R-PICS,the asymmetric catalytic properties of hybrid materials II2 leads to a dramatically decreased after 2 times of cycles.Hybrid materials are characterized by EA,IR and TEM.Through the experiment and the simulation of this paper,some conclusions are obtained.Switching organic moiety from DACH to PICS mainly provided the stereo chemical control of the reaction,indicates that an efficient enantio switching of the aldol adducts could be achieved through the modification of the organic moiety grafted POMs hybrid molecules structure.The immobilization of chiral amines on MNP is realized via electrostatic assemble with POMs.The resulted electrostatic assemblycatalyst could be used by taking advantage of their large framework,high surface area,good dispersion,and efficient separation behavior.However,it also has problems with application development involving general catalytic activity and loss of organic moiety.As the direct result from the high selectivity of organic moiety grafted POMs hybrid molecules,which is the new direction of asymmetric catalysis. |
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