Preparation And Catalytic Application Of Imidazole Salts Supported By SiO₂-g-polymer Brush

In order to achieve the separation and reuse of catalysts,the main catalytic strategies currently used are the homogeneous catalytic-multiphase separation strategy and the insoluble solids loading strategy.The advantage of the homogeneous catalytic-multiphase separation strategy is that the catalyst activity and selectivity are essentially the same as in the homogeneous system,but the disadvantage is that the separation process is more cumbersome.The advantage of the insoluble solids loading strategy is the simplicity of the separation process,but its catalytic activity and selectivity are usually lower than those of the corresponding homogeneous catalysts.Loaded polymer brush catalysts obtained by loading a homogeneous catalyst onto the surface of an insoluble solid have the physical properties of a solid catalyst:rapid separation and reuse of the product is easily achieved;and the chemical properties of a homogeneous catalyst:the catalytic activity is similar to or higher than that of a homogeneous catalyst.In this thesis,loaded polymer brush catalysts were prepared using the atomic transfer radical polymerisation（ATRP）method:a more stable all-carbon chain initiator was chosen to initiate the ATRP polymerisation instead of the commonly used ester-based initiator,in the hope of obtaining a more active and stable polymer brush catalyst.This thesis consists of two parts.The first part is the copolymerisation of vinylimidazole with styrene on the surface of SiO₂ nanoparticles（≈350 nm）containing a solid initiator by ATRP polymerisation to give polymer brush material SiO₂@PVI（2.9）.The polymer brush material 2.9 is then structurally modified:it is reacted with chlorosulfonic acid to give sulfonic acid polymer brush catalyst SiO₂@PVI-SO₃H（2.1）;it is reacted with iodomethane and then ion exchanged with trifluoromethanesulfonic acid to give Neutral catalyst SiO₂@PVI-SO₃CF₃（2.2）.The catalytic performance of catalysts 2.1 and 2.2 was tested using oleic acid esterification,triglyceride exchange and aldehyde protection of p-nitrocinnamaldehyde.The0.1 equivalent catalyst 2.1 catalyzed the oleic acid esterification reaction with 99%conversion in three hours;and the yield remained constant for three cycles,dropping to 50%for the fourth use.The corresponding homogeneous catalyst gave 96%yield in 10 h.The commercially available benzenesulphonic acid catalyst Amberlyst-15 gave 94%yield in 10 h.In the second part,（1R,2R）-1,2-diphenylethylenediamine was used as the starting material to obtain the first ethylene-phenyl-functionalized chiral nitrogen-containing heterocyclic carbene（NHC）precursor in a four-step reaction including Buchwald-Hartwing C-N coupling,Suzuki coupling,and ring closure.ATRP polymerization of the NHC precursor on the surface of SiO₂ nanoparticles with initiator was carried out to obtain the loaded polymer brush precursor SiO₂@NHC.Elemental analysis showed that the loading of chiral NHC in the loaded polymer brush precursor was 0.125 mmol/g.The borohydride reaction of ethyl cinnamate catalyzed by complexing the loaded polymer brush precursor with cuprous chloride gave a catalytic yield of 70%with an ee value of 0.The catalytic yield of the homogeneous catalyst was 90%and the ee value was 32%.