The synthesis and application of polymer immobilised ionic liquid phase catalysts

Abstract

The utilisation of Ionic Liquids (ILs) and Supported Ionic Liquid Phase (SILP) materials in the support of transition metals has been an area of increasing interest in recent years. Drawing from existing literature the Knight-Doherty group has recently developed a range of Ring Opening Metathesis Polymerisation (ROMP) based Polymer Immobilised Ionic Liquid Phase (PIILP) materials for hydrogen peroxide mediated sulfide oxidation and asymmetric carboncarbon bond formation. The aim of this project was to extend this range of materials incorporating novel functionalities via different polymerisation techniques and subsequently utilising these materials in new areas of catalysis. In Chapter 2 of the thesis radical polymerisation was utilised to synthesise two imidazoliumbased cross-linked polymers incorporating different heteroatom donors, to support palladium nanoparticles (NPs) (Scheme A). Scheme A Formation of palladium NPs from imidazolium-based cross-linked polymers. Transmission Electron Microscopy (TEM) along with other techniques was used to determine the size of the NPs which were shown to be in the region of 1.5 nm in diameter. These supported materials were shown to be highly active in the Suzuki-Miyaura cross-coupling of a large range of aryl bromides with phenylboronic acid as part of an extensive catalytic investigation. iv Chapter 3 of the thesis covers the synthesis and characterisation of a range of linear imidazolium-based polymeric supports for the immobilisation of the active Venturello peroxophosphotungstate species [PO4{WO(O2)2}4]3- (Scheme B). Scheme B Reaction pathway to POM@PIILP materials. These amorphous insoluble solid materials were synthesised in high yields requiring no chromatographic purification and fully characterised by a range of techniques. The benzylated imidazolium POM@PIILP III was shown to be highly efficient in the oxidation of a range of sulfides under mild reaction conditions utilising hydrogen peroxide as the oxidant in short reaction times. The kinetics of this system were studied and the relative rates of the first and second oxidations determined. A recycling study showed good promise and POM@PIILP III was transferred to a segmented flow process. High conversion and sulfoxide selectivity was achieved at a residence time of 4 min corresponding to a flow rate of just 1.1 mL min-1 in both ethanol and acetonitrile systems. A lifetime study showed the catalyst to be extremely robust in acetonitrile and a stable activity selectivity profile was achieved under continuous flow conditions over 8 h. Chapter 4 builds upon the work carried out in the previous chapter via the application of POM@PIILP III to the oxidative desulfurisation of model oil. It was shown to be highly efficient and achieved 100 % removal of sulfur in the presence of MeOH after 140 min at 60 oC. Promising recyclability results indicate this system also has future potential for transferral to a flow based system.