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This thesis describes the development of new osmium-mediated methodologies providing novel applications through the use of a third generation of reoxidant for osmium. Chapter 1, The introduction: Summary of past and present methodologies towards the synthesis of the 1,2 amino alcohol motif. Chapter 2, Intramolecular processes: The studies of the tethered aminohydroxylation (TA) of amide and urea derivatives are being investigated. Chapter 3, Investigations towards an intermolecular process: The transposition of the TA methodology to an intermolecular process and the requirements involved are discussed. The role of acetamide is being investigated. Chapter 4, Successful transition to an intermolecular process: Amino acid derivatives became for the first time possible nitrogen sources and were efficiently employed through osmium-mediated reaction to afford interesting biological scaffolds. Chapter 5, Experimental: Full experimental procedures and characterisation of compounds are reported. References: A complete list of citations employed in the previous five chapters is provided. Appendix: Full documentation of X-ray crystal structures, key NMR spectra and HPLC traces is provided.

The acid-mediated osmium-catalysed oxidative cyclisation of 1,2-diols bearing a pendent alkene has been shown to be a powerful method for the formation of cis-2,5-disubstituted tetrahydrofurans. This thesis describes the development of this methodology to broaden the scope of the general reaction, followed by applying the oxidative cyclisation to the synthesis of tetrahydrofuran containing natural products. Introduction: This section reports a range of ractions that osmium oxo-species will facilitate, namely the formation of carbon-oxygen and carbon-nitrogen bonds in a selective manner. In addition to this a variety of similar metal-mediated oxidative cyclisations are discussed. Results and Discussion: The process for optimising the oxidative cyclisation is documented, along with examples which directly compare newly developed methodology with existing methodology. The incorporation of a catalytic amount of a Lewis acid is shown to be more effective than using an excess of a Brønsted acid, with osmium catalyst loading being reduced to 0.2 mol%. Subsequently, this methodology is shown to facilitate the successful oxidative cyclisation of vinyl silanes to form silyl-substituted tetrahydrofurans, along with methodology to “unmask” the silane, as a potential route to lactols. Finally, the application of this methodology to synthesis is demonstrated, with the successful synthesis of neodysiherbaine A being achieved in 7 steps and the C21-30 fragment of pectenotoxin-4 in 12 steps.

A combined experimental and computational study on the reversible ortho-metalation exhibited by the triosmium cluster Os3(CO)10(dppm) (dppm = 1,1-bis(diphenylphosphino)methane is reported. The conversion of nonacarbonyl cluster HOs3(CO)9[-PhP(C6H4)CH2PPh2] to Os3(CO)10(dppm) is independent of added CO and exhibits a significant inverse equilibrium isotope effect (EIE). Reductive coupling of the C-H bond in HOs3(CO)9[-PhP(C6H4)CH2PPh2] leads to the formation of agostic C-H and two distinct aryl-π species prior to the rate-limiting formation of the unsaturated cluster Os3(CO)9(dppm). Heating the unsaturated dimer H2Re2(CO)8 with Cp*Rh(CO)2 (Cp* = 1,2,3,4,5-pentamethylcyclopentadiene) at elevated temperature affords the new trimetallic clusters H2RhRe2Cp*(CO)9 and HRh2ReCp*2(CO)6, and the spiked-triangular cluster HRhRe3Cp*(CO)14. H2Re2(CO)8 reacts with Cp*2Rh2(CO)2 under identical conditions to furnish H2RhRe2Cp*(CO)9 and HRh2ReCp*2(CO)6 as the principal products, in addition to the tetrahedral cluster H2Rh2Re2Cp*2(CO)8. H2RhRe2Cp*(CO)9 undergoes facile fragmentation in the presence of halogenated solvents and the thiols RSH (where R = H, C6H4Me-p) to afford the structurally characterized products Cp*Rh(-Cl)3Re(CO)3, S2Rh3Cp*(CO)4, Cp*Rh(-Cl)(-SC6H4Me-p)2Re(CO)3, and Cp*Rh(-SC6H4Me-p)3Re(CO)3. The new hydrazido-substituted compounds TaCl(NMe2)3[N(TMS)NMe2] (TMS = tetramethylsilyl) and Ta(NMe2)4[N(TMS)NMe2] have been synthesized and their structures established by X-ray crystallography. The latter product represents the first structurally characterized octahedral tantalum(V) complex containing a single hydrazido(I) ligand in an all-nitrogen coordinated environment about the metal center. The fluxional properties of the amido and hydrazido ligands in these new compounds have been established by VT 1H NMR spectroscopy (VT = variable temperature). Preliminary data using Ta(NMe2)4[N(TMS)NMe2] as an ALD (ALD = atomic layer deposition) precursor for the preparation of tantalum nitride and tantalum oxide thin films are presented.

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Transition metal nanoclusters are more active and selective catalysts than their bulk counterparts as the fraction of surface atoms increases with the decreasing particle size. When stabilized in organic or aqueous solutions, they can catalyze many reactions. The catalytic activity of metal nanoclusters depends on the particle size and size distribution. Particle size can be controlled by encapsulating the nanoclusters in the cavities of highly ordered porous materials such as zeolites. In this project, osmium(0) nanoclusters were formed within the void spaces of zeolite. Thus, nanoclusters of certain size were prepared as supported catalyst. Osmium(III) cations were introduced into the cavities of zeolite by ion exchange and were reduced partially or completely to form intrazeolite osmium(0) nanoclusters. The intrazeolite osmium(0) nanocusters were characterized by HRTEM, TEM, EDX, XPS, XRD, ICP-OES spectroscopic methods and N2 adsorption-desorption technique. Intrazeolite osmium(0) nanoclusters were employed as catalyst in the aerobic oxidation of alcohols in organic solution.

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Dispenser cathodes emit electrons through thermionic emission and are a critical component of space-based and telecommunication devices. The emission of electrons is enhanced when coated with a refractory metal such as osmium (Os), osmium-ruthenium (Os-Ru), or iridium (Ir). In this work the microstructure, thermionic emission, and work function of thin film Os-Ru coatings were studied in order to relate microstructural properties and thermionic emission. Os-Ru thin film coatings were prepared through magnetron sputtering and substrate biasing to produce films with an array of preferred orientations, or texture. The effect of texture on thermionic emission was studied in detail through closely-spaced diode testing, SEM imaging, and x-ray diffraction. Results indicated that there was a strong correlation with emission behavior and specific preferred orientations. An ultra-high vacuum compatible Kelvin Probe was used to measure the work function of W-Os-Ru ternary alloy films to determine the effect W interdiffusion has on work function. The results indicated that a high work function alloy coating corresponded to low work function cathodes, as expected. It was inferred that a high work function alloy coating results in a low work function cathode because it aligns more closely with ionization energy of Ba. The results also proved that this method of evaluating dispenser cathode coatings can distinguish small variations in microstructure and composition and may be a beneficial tool in the development of improved dispenser cathode coatings. A novel experimental apparatus was constructed to measure the work function of dispenser cathode coatings in-vacuo using the ultra-high vacuum Kelvin Probe. The apparatus is capable of activating cathodes at high temperature and measuring the work function at elevated temperature. The design of this apparatus allows for more rapid evaluation of dispenser cathode coatings.

Thèse (D. en ressources minérales)--Université du Québec à Montréal, 2005. / En tête du titre: Université du Québec à Montréal. Comprend des réf. bibliogr. Publié aussi en version électronique.

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