Study On Synthesis Of Inorganic-Organic Hybrid Compounds Based On Polyoxometalates And Their Catalytic Oxidation Performance For Thioethers

Polyoxometalate(POM),as the multinuclear complexes with redox and acid properties,could be the high-performance catalysts due to their the soft base character,through the controllable molecular design and synthetic method.Selective oxidation of thioethers,affords diverse sulfoxides and sulfones,is an important method in synthesis of fine chemicals.And it can also degrade the toxic or pungent chemicals,such as 2-chloroethyl ethyl sulfide(CEES).However,most of POMs are usually soluble in solvents,causing difficulities in recovery and recycling of the catalysts.By combining POMs with metal cations and organic ligands to get the hybrid inorganic-organic heterogeneous compounds is an important way to solve the problems.Based on these considerations,it is highly desirable and significant to design new POMs materials with high activity and selectivity for catalytic oxidation of thioethers.In this paper,we have obtained a series of inorganic-organic hybrid POMs through the self-assembly between the heteropolymolybdates and different containing N-donor ligands,carboxylic acid ligands.The selective oxidation of thioethers have also been systematically studied in the presence of these compounds,which provide theoretical guidance for the synthesis and design of catalysts based on POMs.(1)Four new high-dimensional hybrid architectures containing Evans-Showell-type POMs and Cu-organic subunits were obtained.Compound 1 represents the first 3D host-guest structure constructed from Evans-Showell-type POM.More interestingly,four hybrid compounds as heterogeneous catalysts show high activity and interesting selectivity in the oxidation reactions of sulfides.In presence of 1,the methyl phenyl sulfide can be almost converted to the corresponding sulfoxide with 100%selectivity,which achieved the high activity and high selectivity for catalyzing sulfides.(2)Through the conventional method,thirteen dimeric hybrid compounds have been synthesized through self-assembly.These dimeric compounds are isostructural and obtained by combining two modified POM clusters {P/As/Te/SeMo6(PABA)3} with transiton metal cations.All these compounds can efficiently catalyze various thioethers(phenyl sulfide and sulfur mustard simulant 2-chloroethyl ethyl sulfide(CEES))through the heterogeneous manner.According to the catalytic mechanism of these POMs,we find that the catalytic activity are original form the PABA modified POMs {P/As/Te/SeMO6(PABA)3} and the transition metal cations(Co>Ni,Zn,Mn).And the center atom of heteropolymolybdates also play certain role on the oxidation of thioether.(3)Four dimeric hybrid compounds and four 1D chain hybrid compounds have been synthesized through self-assembly.All the 1D chains are isostructural and represent the first extended architectures constructed from two different organic ligands modified polyoxometalate.As the heterogeneous catalyst,these compounds not only exhibit excellent catalytic activity in selective oxidation of thioethers,but no obvious change of the catalytic activity was found for the following 10 cycles.Within 16 min,methyl phenyl sulfide can almost convert to sulfoxide,and CEES was high-selectively oxidized to the corresponding nontoxic 2-chloroethyl ethyl sulfoxide(CEESO)within 5 min.By comparing the catalytic performances with the third chapter,we find that the carboxylic acid ligands also produce certain role on the oxidation of thioethers:PABA>PHBA/Ala/Ac.