Doctoral Degrees (Chemistry)

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Browsing Doctoral Degrees (Chemistry) by Advisor "Bezuidenhout, Ben"

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    Bulky metal complexes as model nanoscale catalysts
    (University of the Free State, 2012-11) Young, Cyril; Roodt, Andreas; Bezuidenhout, Ben
    English: The lifestyle of modern society has created a massive demand for various chemicals such as fuels, chlorine-free refrigerants, high-strength polymers, stain-resistant fibres, cancer treatment drugs and thousands of other products. The demand for these compounds can only be met through the use of catalysts. Heterogeneous catalysis has become a fundamental part of the industrial scale production of these chemicals. Although heterogeneous catalysis is better suited for these processes than its homogeneous counterpart, some of the systems are plagued by poor distribution of the active metal species throughout the support. The aim of this study was to investigate the feasibility of synthesising robust, planar, bridging ligands that could act as spacers between active metal species in the deposition of active catalysts onto heterogeneous supports. By choosing different building blocks, for the simple Schiff base reaction, the distance and proximity between active metal species could theoretically be controlled for a desired application. 1,10-Phenanthroline and diamide type ligands (Figure 1) were identified as possible candidates for this application Figure 1: Different ligand systems identified as possible dispersion spacers. (A) represents the diamide type ligands and (B) the 1,10-phenanthroline ligands. The aim of this study was pursued by the identification and synthesis of building blocks such as 5,6-diamino-1,10-phenanthroline and 1,10-phenanthroline-5,6-dione which could act as bridging ligands and could be used to construct larger bridging systems. The bridging ligands and building blocks were coordinated to square planar metal centres such as platinum and palladium. This would enhance the possibility of creating a single layer network on the surface of the support. The ligands and complexes were characterised using solid state techniques and single crystal X-Ray Diffractometry to investigate the planarity of these species and the coordination mode to some of the diamide type complexes that have not found many applications in this field. The Heck coupling was identified as a standard reaction which could be utilised to test the catalytic properties of the palladium species. The catalytic activity of a range of diamide and 1,10-phenanthroline type ligands was evaluated after the optimisation of the Heck coupling. It was found that reducing the electron density on the five and six position of the phenanthroline ring drastically enhances the catalytic capabilities of these compounds. The diamide type complexes and larger bridging ligands showed less promising results.