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Since the discovery of Wilkinson’s catalyst and its usefulness in the homogeneous hydrogenation of olefins many investigations have been carried out on trivalent, tertiary phosphine–rhodium complexes.¹ Studies have shown that N-Heterocyclic carbenes as ligands offer increased stability to the complex and possess similar electronic properties as phosphine ligands.² The applications of the traditional catalyst are limited due to the limited stability of its solutions and its susceptibility to attack from the environment i.e. oxygen and moisture. The hydrogenation of olefins and other unsaturated compound is of great importance for the fine chemical and petroleum industries. The aim is to produce more stable and active versions of the traditional catalyst and also to demonstrate their improved stability and activity in catalytic applications. This study involves the investigation of the effects of ligand modification on Wilkinson type hydrogenation catalysts. Five Rhodium-phosphine complexes 1a: Rh(PPh₃)₃Cl, 1b: Rh(PPh₂Me)₃Cl, 1c: Rh(PPh₂Et)₃Cl, 1d: Rh(PPhMe₂)₃Cl, 1e: Rh(PPhMe₂)₃Cl have been synthesised and characterised by means of melting point,¹H NMR, ¹³C NMR, ³¹P NMR, IR and Mass Spectroscopy. Complexes 1d and 1e have also been characterised by means of elemental analysis and single crystal XRD. Five rhodium-N-heterocyclic carbene complexes 2a: Rh(COD)ImesCl [Imes =1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] , 2b: Rh(COD)(diisopropylphenyl)₂Cl 2c: Rh(COD)(adamantyl)²Cl, 2d: Rh(COD)(diisopropyl)²Cl 2e: Rh(COD)(ditertbutyl)²Cl have been synthesised and characterised by means of melting point, ¹H NMR, ¹³C NMR, IR and Mass Spectroscopy. Five rhodium-NHC-CO complexes 3a: Rh(CO)₂ImesCl, 3b: Rh(CO)₂(diisopropylphenyl)₂Cl, 3c: Rh(CO)₂(adamantyl)₂Cl , 3d: Rh(CO)₂(diisopropyl)₂Cl, 3e: Rh(CO)₂(ditertbutyl)₂Cl, have been synthesised and characterised by means of ¹H NMR, ¹³C NMR, IR and Mass Spectroscopy. Complexes 1a, 1d, 1e, 2a, 2b, 2c, 2d, 2e were tested in the hydrogenation of simple alkenes under mild conditions. For the rhodium-phosphine complexes the catalyst efficiency based on TOF increases in the following order: 1a > 1d > 1e or RhCl₃(PPhMe₂)₃ > RhCl₃(PPhEt₂)₃ > RhCl(PPh₃)₃. For the rhodium-(COD)-NHC complexes catalyst efficiency based on TOF increases in the following order: 2d > 2b > 2e > 2a > 2c. While rhodium-phosphine complexes are far more active than rhodium-(COD)-NHC complexes, the latter seem to be active for a longer time and hence more stable under mild hydrogenation conditions. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2010.

Semiconductor nanocrystals exhibit unique optical and physical properties that make them an attractive alternative to organic dyes for fluorescent bioapplications. Although significant advances have been made since their first reported use in biology a decade ago, it still remains a challenge to prepare high quality, biocompatible semiconductor nanocrystals. / In this thesis, studies are described with the aim to prepare robust, biocompatible semiconductor nanocrystals that exhibit each of the properties necessary for their implementation in biological applications. Two different approaches were investigated: ligand exchange and polymer encapsulation, and advances in each are presented. A heterobifunctional ligand suitable for bioconjugation, carboxyl terminated dihydrolipoic acid poly(ethylene glycol) (DHLA-PEG-COOH), was synthesised and characterised to prepare water-soluble, biocompatible semiconductor nanocrystals via ligand exchange. It was found that nanocrystals transferred into water using DHLA-PEG-COOH exhibit the same optical properties and colloidal stability as those prepared using DHLA-PEG. It was demonstrated that the surface charge of the nanocrystals may be controlled by altering the ratio of DHLA-PEG:DHLA-PEG- COOH ligands. In a different approach, colloidally stable, biocompatible nanocrystals were prepared via polymer encapsulation. It was found that by employing a low molecular weight polymer, biocompatible nanocrystals that exhibit a small hydrodynamic diameter could be realised. / Experimental results are presented on the conjugation of biocompatible nanocrystals to protein targets. It was found that while standard coupling chemistries yield protein-dye conjugates, these chemistries did not result in protein-nanocrystal conjugates. In order to overcome the drawbacks of standard coupling chemistries, which are susceptible to hydrolysis, a novel conjugation scheme utilising copper-free click chemistry is proposed. / Finally, the success of nanocrystals in bioapplications depends on the ability to characterise nanocrystal-protein conjugates. By means of analytical ultracentrifugation, data on the sedimentation properties of nanocrystals and nanocrystal-protein conjugates was obtained. Analysis of these data provided information on fundamental physical properties of biocompatible nanocrystals and nanocrystal-protein conjugates, in particular the core crystal size, hydrodynamic size, number of surface ligands and nanocrystal:protein stoichiometry. Such a precise, comprehensive characterisation of nanocrystals in general, and nanocrystal-protein conjugates in particular, will greatly facilitate their use in bioapplications.

Thesis (M.S.)--Brigham Young University. Dept. of Chemistry and Biochemistry, 2005. / Includes bibliographical references.