Thesis (Ph. D.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1971. / Typescript. Vita. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

- / -

Ruthenium carbene complexes, with the general structure, [LL’Ru=CHR], are commonly known as Grubbs type catalysts, named after the discoverer of these metathesis catalysts. The discovery was quite revolutionary, since the catalysts proved to be easy to handle, tolerant towards various functional groups and more stable with regard to air and water than previous transition metal catalysts. Another important advantage was that all types of olefin metathesis reactions could be initiated without the help of co-catalysts or promoters. Today Grubbs type catalysts find wide application in especially organic and synthetic chemistry. A well-known example is the SHOP-process which produces long chain -olefins, while other important applications include the synthesis of macro-cyclic and cyclic olefins. The current study involved experimental and theoretical work to investigate various aspects comprising synthetic procedures, reactivity, kinetics, geometry and electronic properties of the complexes. Results are discussed briefly in the following paragraphs. The first aim of the project was to synthesise a Grubbs type catalyst. Initial efforts were focused on the preparation of a first generation catalyst through various methods. This included modifying the reported method for the synthesis of [(PPh3)2Cl2Ru=CH-CH=CMe2] to yield [(PPh2Cy)2Cl2Ru=CHCH= CMe2] instead; a phosphine exchange reaction with the complex [(PPh3)2Cl2Ru=CH-CH=CMe2] and free phosphine PPh2Cy; and utilising the analogue arsine ligand, AsPh3, to synthesise [(AsPh3)2Cl2Ru=CHCH=CMe2]; but unfortunately no success was achieved. However, it was possible to synthesise a novel second generation Grubbs type catalyst, [(IMesH2)(PPh2Cy)Cl2Ru=CHPh], through the phosphine exchange reaction of [(IMesH2)(NC5H5)2Cl2Ru=CHPh] and PPh2Cy. The new complex was tested in kinetic reaction studies and phosphine exchange reactions. Results showed that [(IMesH2)(PPh2Cy)Cl2Ru=CHPh] was catalytically active for the ring closing metathesis of commercial diethyl diallylmalonate. The reaction was first order with regard to the olefin, contrary to the second order kinetic results reported for similar reactions catalysed by first generation Grubbs catalysts. The phosphine exchange reactions were very successful and a rate constant could be determined. The rate constant was independent of the free phosphine concentration and activation parameters had relatively large, positive values; results indicative of a dissociative mechanism. These findings are in correlation with literature reports. A kinetic investigation was done on the catalyst-olefin coordination involving the functionalized olefins vinyl acetate, allyl acetate and allyl cyanide; and the first generation Grubbs catalyst, [(PCy3)2Cl2Ru=CHPh]. A two-step rate law, similar to an interchange mechanism, was determined. Phobcat, [(PhobCy)2Cl2Ru=CHPh], is modified first generation Grubbs type catalyst with rigid bicyclic phosphine rings which was recently developed by the Sasol Homogeneous Metathesis Group. In the current study Phobcat was compared to Grubbs1-PCy3 in the cross metathesis reaction of 1-octene. Results showed that Phobcat was up to 60% more active and had a 5 hour longer lifetime than Grubbs 1-PCy3. Theoretical studies were done on the three functionalized olefins of the earlier experimental study to gain fundamental understanding of steric and electronic influences on these catalyst-olefin systems. Without exception, coordination via the heteroatom of the olefin was significantly more favourable than coordination via the double bond functionality. This result indicates that metathesis of these olefins is highly unlikely, since the stable heteroatom coordination will suppress the parallel Ru=C/C=C interaction which is compulsory for the metathesis reaction. Orbital studies highlighted the difference between coordination of acetate and cyanide, but no trend of an electronic nature could be recognised. / Prof. A. Roodt

The aim of this investigation was to study model complexes containing strong p- ligands as potential nitrogen, oxygen and ligand transfer catalysts. Nitrido containing cyano complexes of group 6 to 8 metals were selected as potential nitrogen transfer catalysts. Solid state and solution studies, investigating different aspects of these systems, were performed. Finally, the knowledge on mechanistic studies were applied to selected examples of 1st generation Grubbs catalyst [Ru(=CR)(PX3)2Cl2] (=CR = carbene) to investigate olefin coordination and oxygen decomposition reactions (both involving strong p-interactions at the metal center thereof). / Prof. A. Roodt

The development of procedures for the synthesis of valuable organic molecules constitutes an important part of chemistry. The goal of improving the efficiency of existing methodologies can be fulfilled by use of metal catalysts. Recent developments in the field of homogeneous gold catalysis have contributed to these efforts and continued investigations assure future innovations. Chapter 1 summarises the properties of gold and ligand-supported gold(I) complexes and demonstrates how a detailed understanding of its reactivity and possible bonding interactions with various substrates facilitates the development of well-defined catalytic systems. Particular attention is given to N-heterocyclic carbenes, highly tunable ligands that stabilise a wide range of different transition metal complexes. Three chapters describe syntheses and studies of known and new complexes. Chapter 2 discusses expedient syntheses of key NHC-gold(I) complexes and catalysts. Chapter 3 constitutes studies to the behaviour of the commonly used tetrafluoroborate counterion in a particular IPrCl -gold(I) complex. Chapter 4 de- scribes the synthesis of a range of IPr-gold(I) carbanion complexes from the widely studied IPr-gold(I) hydroxide synthon, the study of their properties and exploration of their reactivity. Catalytic applications in transformations of alkynes and alcohols are described in the last three chapters. Chapter 5 details the development of efficient NHC-gold(I)-catalysed procedures for the synthesis of vinyl ethers through addition reactions of aliphatic and benzylic alcohols to alkynes. Benzylic alcohols were found to undergo gold-catalysed dehydration under specific conditions and Chapter 6 discloses the NHC-gold(I)-catalysed dehydrative formation of ethers from phenols and benzylic alcohols. Appendix A describes preliminary explorations to the complimentary use of Brønsted acidic compounds as catalysts for the formation of products with new C – C bonds from benzylic alcohols and phenols.

Ph.D. / Compounds, 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L1) and 2,6-bis(3,5-ditertbutylpyrazol-1-ylmethyl)pyridine (L2) were prepared by phase transfer alkylation of 2,6-bis(bromomethyl)pyridine with two mole equivalents of the appropriate pyrazole. Ligands L1 and L2 reacted with either [PdCl2(NCMe)2] or [PdClMe(COD)] to form mononuclear palladium complexes [(PdCl2(L1)] (1), [(PdClMe(L1)] (2), [(PdCl2(L2)] (3), [(PdClMe(L2)] (4). All new compounds prepared were characterised by a combination of 1H NMR, 13C NMR spectroscopy and microanalyses. The coordination of L2 in a bidentate fashion through the pyridine nitrogen atom and one pyrazolyl nitrogen atom has been confirmed by single crystal X-ray crystallography of complex 3. Reactions of 1, 2 and 3 with the halide abstractor NaBAr4 (Ar = 3,5-(CF3)2C6H3) led to the formation of the stable tridentate cationic species [(PdCl(L1)]BAr4 (5), [(PdMe(L1)]BAr4 (6) and [(PdCl(L2)]BAr4 (7) respectively. Tridentate coordination of L1 and L2 in the cationic complexes has also been confirmed by single X-ray crystallography of complexes 5 and 6. The analogous carbonyl linker cationic species, [Pd{(3,5-Me2pz-CO)2-py}Cl]+ (9) and [Pd{(3,5-tBu2pz-CO)2-py}Cl]+ (10), prepared by halide abstraction from [Pd{(3,5-Me2pz-CO)2-py}Cl2] and [Pd{(3,5-tBu2pz-CO)2-py}Cl2] with NaBAr4, were however less stable. While cationic complexes 5-7 showed indefinite stability in solution, 9 and 10 had t1/2 of 14 and 2 days respectively. Attempts to crystallise 1 and 3 from the mother liquor resulted in the isolation of the salts [PdCl(L1)]2[Pd2Cl6] (11) and [PdCl(L2)]2[Pd2Cl6] (12). Although when complexes 1-4 xviii were reacted with modified methylaluminoxane (MMAO) or NaBAr4, no active catalysts for ethylene oligomerisation or polymerisation were formed, activation with silver triflate (AgOTf) produced active catalysts that oligomerised and polymerised phenylacetylene to a mixture of cis-transoidal and trans-cisoidal polyphenylacetylene. Compounds 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L3) and 2-(3,5-di-tert-butylpyrazol-1-ylmethyl)pyridine (L4) were prepared by phase transfer alkylation of 2-picolylchloride hydrochloride with one mole equivalent of the appropriate pyrazole. Compounds 2-(3,5-bis-trifluoromethyl-pyrazol-1-ylmethyl)-6-(3,5-dimethyl-pyrazol-1-ylmethyl)-pyridine (L5) and 2-(3,5-dimethyl-pyrazol-1-ylmethyl)-6-phenoxymethyl-pyridine (L6) were isolated in good yields by reacting (2-chloromethyl-6-3,5-dimethylpyrazol-1-ylmethyl)pyridine with an equivalent amount of potassium salt of 3,5-bis(trifluoromethyl)pyrazolate and potassium phenolate respectively. L3-L6 react with either [Pd(NCMe)2Cl2] or [PdClMe(COD)] to give mononuclear palladium complexes 13-18 of the general formulae [PdCl2(L)] or [PdClMe(L)] where L = is the bidentate ligands L3, L4, L5 and L6 respectively. Single crystal X-ray crystallography of complexes 13, 15 and 16 has been used to confirm the solid state geometry of the complexes. In attempts to generate active olefin oligomerisation catalysts, the chloromethyl Pd(II) complexes 14 and 16 were reacted with the halide abstractor NaBAr4 in the presence of stabilising solvents (i.e Et2O or NCMe) but no catalytic activities were observed. Decomposition was evident as observed from the deposition of palladium black in experiments using Et2O. In experiments where NCMe was used as the stabilising solvent, the formation of cationic species stabilised by NCMe was evident from 1H NMR analyses. Reaction of complex 14 with NaBAr4 on a preparative scale in a mixture of CH2Cl2 and NCMe solvent gave the cationic complex [[PdMeNCMe(L3)]BAr4 (19) in good yields. Complex 17 reacted with NABAr4 to give tridentate cationic species [[PdMe(L5)]BAr4 (20) which is inactive towards ethylene oligomerisation or polymerisation reactions. The tridentate coordination of L5 in 20 has also been established by single crystal X-ray structure of 20. Catalysts generated from 18 and 19 catalysed ethylene polymerisation at high pressures to branched polyethylene; albeit with very low activity. The Choromethyl palladium complex 14 reacted with sulfur dioxide to form complex 21. The nature of the product has been established by 1H NMR, 13C NMR and mass spectrometry to be an insertion product of SO2 into the Pd-Me bond of 14. Compounds L1-L4 reacted with the nickel salts NiCl2 or NiBr2 in a 1:1 mole ratio to give the nickel complexes [NiCl2(L1)] (22), [NiBr2(L1)] (23), [NiCl2(L2)] (24), and [NiBr2(L2)] (25), [Ni2(μ2-Cl)2Cl2(L3)2] (26), [Ni2(μ2-Br)2Br2(L3)2] (27), [NiCl2(L4)] (29) and [NiBr2(L4)] (30) in good yields. Reaction of L3 with NiBr2 in a 2:1 mole gave the octahedral complex [NiBr2(L4)2] (28) in good yields. Complexes 22-30 were characterised by a combination micro-analyses, mass spectrometry and single crystal X-ray analyses for 27 and 30. No NMR data were acquired because of the paramagnetic nature of the complexes. When complexes 22-30 were activated with EtAlCl2, highly active olefin oligomerisation catalysts were formed. In the ethylene oligomeristion reactions, three oligomers: C11, C14 xx and C16 were identified as the major products. Selectivityof 40% towards α-olefins were generally obtained. In general catalysts that contain the bidentate ligands L3 and L4 were more active than those that contain the tridentate ligands L1 and L2. Dichloride complexes exhibited relatively higher catalytic activities than their dibromide analogues. Turn over numbers (TON) for oligomer formation showed high dependence on ethylene concentration. A Lineweaver-Burk analysis of reactions catalysed by 22 and 26 showed TON saturation of 28 393 kg oligomer/mol Ni.h and 19 000 kg oligomer/mol Ni.h respectively. Catalysts generated from complexes 22-30 also catalysed oligomerisation of the higher olefins, 1-pentene, 1-hexene and 1-heptene and displayed good catalytic activities. Only two products C12 and C15 were obtained in the 1-pentene oligomerisation reactions. The 1-hexene reactions also gave two products, C12 and C18, while 1-heptene oligomerisation reactions gave predominantly C14 oligomers. Five benzoazoles were used to prepare a series of palladium complexes that were invesitigated as Heck coupling catalysts. The compounds 2-pyridin-2-yl-1H-benzoimidazole (L7) and 2-pyridin-2-yl-benzothiazole (L8) were prepared following literature procedures. The new ligands 2-(4-tert-butylpyridin-2-yl)-benzooxazole (L9) and 2-(4-tert-butyl-pyridin-2-yl)-benzothiazole (L10) were prepared by ring closure of aminophenol and aminothiophenol with tert-butyl picolinic acid respectively. The ligand 6-tert-Butyl-2-(4-tert-butyl-pyridin-2-yl)-benzothiazole (L11) was prepared by intramolecular cyclisation under basic conditions is described. Reactions of L7-L11 with either [Pd(NCMe)2Cl2] or [Pd(COD)MeCl] afforded the corresponding mononuclear palladium complexes [PdClMe(L7)] (31), [PdClMe(L8)] (32), [PdCl2(L9)] (33), [PdMeCl(L9)] (34), [PdCl2(L10)] (5), [PdMeCl(L10)] (36) and [PdMeCl(L11)] (37) as xxi confirmed by mass spectrometry and micro-analyses. The palladium complexes 31-37 were efficient Heck coupling catalysts for the reaction of iodobenzene with butylacrylate under mild conditions and showed good stability.

In part 1 of this thesis, the antidiabetic activity of a series of novel oxovanadium(IV) complexes was investigated. A range of bidentate N,O-donor ligands, which partially mimic naturally occurring bioligands, were prepared and reacted with the vanadyl ion to form the corresponding bis-coordinated complexes. Initially, 2-(2ˊ-hydroxyphenyl)-1R-imidazoline (where R = H, ethyl and ethanol) ligands were prepared. The aqueous pH-metric chemical speciation was investigated using glass electrode potentiometry which allowed for the determination of protonation and stability constants of the ligands and complexes, respectively. The species distribution diagrams generated from this information gave an indication of how the complexes might behave across the broad pH range experienced in the digestive and circulatory systems. This information was used to create an improved 2nd generation of ligands that were constructed by combining the imidazole and carboxylic acid functionalities. These corresponding bis[(imidazolyl)carboxylato]-oxovanadium(IV) complexes displayed a broader pH-metric stability. Both sets of complexes improved glucose uptake and reduced coagulation in vitro. In part 2 of this thesis, a range of homogeneous and heterogeneous oxovanadium(IV) catalysts were prepared. Firstly, Merrifield beads were functionalized with ligands from Part 1 and then reacted with vanadyl sulfate to afford the corresponding heterogeneous catalysts. These displayed promising catalytic activity for the peroxide facilitated oxidation of thioanisole, styrene and ethylbenzene as well as the oxidative bromination of phenol red. Smaller imidazole-containing beads with higher surface areas than the Merrifield beads were prepared by suspension polymerization. These beads similarly demonstrated excellent catalytic activity for the oxidation of thioanisole and were highly recyclable. In attempt to increase the exposed catalytic surface area, while retaining the ease of separation achieved in the before mentioned systems, micron to nano sized electrospun fibers containing coordinating ligands were fabricated. The corresponding oxovanadium(IV) functionalized fibers were applied to the oxidation of thioanisole using a continuous flow system. The flexible and porous nature of the fiber mats was well suited to this approach. After optimization of the reactant flow rate and catalyst amount, near quantitative (> 99%) oxidation was achieved for an extended period. In addition, leaching of vanadium was mitigated by modification of the attached ligand or polymer material.

The major topics discussed are all relevant to the bright phosphorescent emissions of coinage metal complexes (Cu(I), Ag(I) and Au(I)) with an explanation of the theoretical background, computational results and ongoing work on the application in materials and optoelectronic devices. Density functional computations have been performed on the majority of the discussed complexes and determined that the most significant distortion that occurs in Au(I)-phosphine complexes is a near and beyond a T-shape within the P-Au-P angle when the complexes are photoexcited to the lowest phosphorescent excited state. The large distortion is experimentally qualified with the large Stokes' shift that occurs between the excitation and emission spectra and can be as large as 18 000 cm-1 for the neutral Au(I) complexes. The excited state distortion has been thoroughly investigated and it is determined that not only is it pertinent to the efficient luminescence but also for the tunability in the emission. The factors that affect tunability have been determined to be electronics, sterics, rigidity of solution and temperature. The luminescent shifts determined from varying these parameters have been described systematically and have revealed emission colors that span the entire visible spectrum. These astounding features that have been discovered within studies of coinage metal phosphorescent complexes are an asset to applications ranging from materials development to electronics.