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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Improved and new iron-catalysed cross-coupling reactions

Pye, Dominic Richard January 2014 (has links)
Iron-catalysed cross-coupling chemistry is undergoing a renaissance due advantages in cost, toxicity and abundance compared to traditional cross-coupling catalysts. In Chapter 2 it is shown that expensive, synthetically challenging bis-phosphines used in the iron-catalysed cross-coupling of alkyl halides and arylboronic acid pinacol esters can be replaced in many cases with simple iron salts in phosphine-free procedures. More challenging substrates require the use of cheap, widely available bis-phosphines such as dppe (l,2-bis(diphenylphosphino)ethane) or dppp (1,3- bis(diphenylphosphino)propane). An EPR spectrum of the reaction mixture shows the presence of previously reported iron(l) complex [FeBr(dppehL which is the likely resting state in the catalytic cycle. Kinetic studies indicate oxidative addition of the alkyl halide via single-electron transfer to a three-coordinate iron species to be the rate-determining step. Having demonstrated that the key feature for facilitating iron-catalysed Suzuki coupling is the activation of a boronic acid pinacol ester with an organometallic nucleophile, in Chapter 3 it was shown that this form of activation could be applied to bis(pinacolato)diboron, allowing the iron catalysed borylation of alkyl, allyl, benzyl and, to a lesser extent, aryl halides. A unique, low-valent, phosphine-supported iron-boryl complex, [Fe(Bpin)(dpbzhL (pin = pinacolato) was isolated from the reaction of [FeCI₂(dpbz)₂] (l,2-bis(diphenylphosphino)benzene) and Li[B₂pin₂(¹Bu)], however this complex failed to react in stoichiometric reactions with 1- bromobutane, reflecting the finding that excess phosphine greatly retards the rate of ironcatalysed borylation. The uniqueness of these low-valent iron-boryl intermediates provided an opportunity to investigate new forms of catalysis based on these complexes. Chapter 4 describes attempts to catalyse the boryl/electrophile difunctionalisation of styrene using Li[B₂pin₂(¹Bu)) and iron precatalysts. It was found that stoichiometric iron is capable of mediating the boryl protonation of styrene; however attempts to trap the organometallic intermediate proved fruitless, and deuterium labelling studies were unable to determine the origin of the a-hydrogen in the resultant product. In order to expand the utility of iron-catalysed cross-coupling, in Chapter 5 attempts to couple electrophiles ·derived from enantiomerically pure l,2-amino alcohols are described. A range of electrophiles including l,2-amino halides, cyclic sulfamidates, oxazolidinones, and oxazolinethiones were screened for activity in iron- and nickel-catalysed cross-coupling; however none of these furnished the desired products.

Precipitation of calcium sulfates on modified cellulose interfaces

Nissinen, Tomi Pekka Bernhard January 2014 (has links)
Precipitation of calcium sulfates has been investigated on modified cellulose interfaces and in situ. Spin-coated cellulose thin films were used as model substrates to investigate the crystallization of calcium sulfate dihydrate (gypsum) under industrially relevant conditions using highly concentrated dispersions of calcium sulfate hemihydrate (bassanite). The films were pre-treated in aqueous solutions of calcium, magnesium or iron ions, where regeneration in a solution of Ca 2 + promoted gypsum crystallization on the polysaccharide substrate in the presence of bassanite or in control solutions comprising supersaturated calcium sulfate. Cellulose-bassanite hybrid thin films were also applied as crystallization substrates for gypsum from a dispersion of bassanite. Hybrid thin films were prepared by adding bassanite into a mixture of dissolved polymeric cellulose and nmethyl- morpholine-n-oxide (NMMO) before regeneration of the cellulose structure. The bassanite aggregates acted as crystal growth sites for gypsum, which promoted the crystal growth of gypsum on the hybrid thin film substrate. In situ characterisation of the precipitation of gypsum on the cellulose interface with Raman spectroscopy and X-ray diffraction showed the crystallization to proceed via a bassanite intermediate phase in a solution of calcium and sulfate ions. The existence of the otherwise thermodynamically unstable phase was attributed to the stabilizing effect of dissolved polymeric cellulose and dehydrated NMMO. Precipitation of calcium sulfates in situ produced nanoparticulate amorphous calcium sulfate within a cellulose polymer network. The composite material was prepared by adding aqueous solutions of calcium and sulfate ions into NMMO prior to the dissolution of cellulose, where the hydration of NMMO controlled the transformation of amorphous calcium sulfate to crystalline gypsum.

Thermal stability and deformation of nanocrystalline nickel

Darnbrough, J. E. January 2014 (has links)
This work is conducted on nanocrystalline nickel using a range of novel techniques in order to investigate the thermal stability of the microstructure and the mechanical properties of subsequent microstructures. Work is focused on two sources of nanocrystalline nickel produced via electrodeposition with varying levels of impurity sulphur. Impurity sulphur alters the thermal stability of the material; a low sulphur system is stable up to a temperature of 400°C and then coarsens normally to produce a micro-polycrystalline structure, a high sulphur material coarsens at 300°C and the coarsening quickly stagnates leaving a stable microstructure of rv550nm grains. Above 485°C, the high sulphur material is observed to undergo abnormal growth of large planar faceted grains. Observation of the growth post heat treatment via standard electron microscopy techniques gave statistical data complemented by in-situ heat treatment scanning electron microscopy and high temperature resistivity measurement tests to elucidate the stages of growth. A range of macro and micro scale tests were undertaken to investigate the physical properties of the materials; from Vickers hardness and four point bend, to novel in-situ micro-cantilever bend tests. The effect of the increased grain size from heat treatment leads to a reduction in the hardness and yield strength of the materials and in the case of the high sulphur material, segregation of the impurity to the grain boundary led to a ductile to brittle transition.

Ultrasonic studies of the electronic structure of cadmium crystals

Peck, David Raymond January 1970 (has links)
No description available.

Selective oxidation reactions catalysed by Palladium (II)

Dornan, Laura M. January 2016 (has links)
Carbonyls are an extremely important class of compounds and have been used in many different industries, including pharmaceuticals, fine chemicals, polymers and bulk commodities. The synthesis of carbonyl compounds through the oxidation of an alcohol or an alkene is an inherently straightforward protocol but despite this, oxidation reactions tend to be avoided industrially. This avoidance can be attributed to the lack of useful and safe methods for oxidation reactions. In this thesis, the oxidation of both alcohols and alkenes to their corresponding carbonyl compounds will be investigated using Pd(ll) catalysis. In Chapter two, the aerobic oxidation of alcohols will be examined using N,O-ligated Pd(ll) complexes. The substrate scope of the reaction will be investigated and methods to increase the turnover number (TON) will be explored. In Chapter three, the use of electron transfer mediators (ETMs) will be examined as a method to increase the TON of aerobic alcohol oxidation. Polyoxometalates will be compared to other traditional ETMs and the applicability of this system to a range of substrates will be studied. In Chapter four, the use of cationic Pd(ll) complexes will be explored for Wacker-type oxidation of terminal alkenes to methyl ketones using hydrogen peroxide. The mechanism of oxidation will be examined through kinetic studies, isotopic labelling and electrospray ionisation spectroscopy.

Exploring and developing candidate materials for production of transition metal based synthetic ferrimagnets

Forbes, Colin Malcolm January 2016 (has links)
Through the exploration and development of candidate materials it was discovered that a a variety of transition metals could be coupled together via a range og non-magnetic materials to produce several synthetic ferrimagnets (SFiM). These SFiM exhibited a wide range of magnetic properties were the optimum SFiM was achieved through coupling the A1 FePt phase to Co via a non-magnetic Ru layer. From the development of these optimum SFiM structures it was found that the multi-layered structures were much more thermally robust in comparison to the tri-layer structures. Through structural analysis it was discovered that this thermal stability was not a result of interlayer mixing or grain growth. Therefore it was demostrated that a variety of SFiM structures could be produced for applications such as all optical switching.

Impact-parameter calculations : application to proton-hydrogen and He p2 s - hydrogen collisions

Morrison, Hugh Gerard January 1977 (has links)
No description available.

Reactions of hydridocarbonyltertiaryphenylphosphine complexes of iridium

Morrison, Robert John January 1971 (has links)
No description available.

Some solid state reactions of transition metal oxides

Pick, A. N. January 1973 (has links)
No description available.

Rapid radiochemical separations of americium from actinides, mixed fission products and matrix elements

Higginson, Matthew January 2015 (has links)
In analysis of complex nuclear forensic matrices containing lanthanides, actinides and matrix elements, rapid selective extraction of Am/Cm for quantification is challenging due to the difficult separation of Am/Cm from lanthanides. This project attempts to develop novel separation processes for Am/Cm separation utilising liquid-liquid extraction and extraction chromatography based on soft N-donor triazine extractants. Selective extractants were identified and synthesized and a liquid-liquid separation procedure was developed. Of these ligands, CyMe4-BTPhen, CyMe4-BTBP, CA-BTP and CA-BTPhen were compared for application to complex matrices. The developed process allows for purification and quantification of Am and Cm (recoveries 80–100%) and other major actinides in < 2 days without the use of multiple columns or thiocyanate, yielding a full data set. The process developed was shown to be unaffected by Ca/Fe/Al (10 mg mL-1) and thus requires little pre-treatment of samples. Due to limited availability of media for separation of americium using EC, we synthesized and tested a novel covalently-linked EC resin, utilising a triazine soft N-donor (Me4BTPhen) extractant for americium extraction. The resin was generated by conjugation of a Me4BTPhen derivative with poly(vinylbenzyl) chloride to generate PVB-Me4BTPhen. PVB-Me4BTPhen was shown to extract americium from a complex matrix simulating nuclear forensic samples, and containing lanthanides, actinides and matrix elements with high Am (III) recovery ( > 90%) and low extraction of other elements, and provides an alternative separation process for Am (III) extraction. Adsorption was also investigated as an alternative, more flexible approach to resin preparation. BTBP/BTPhen Am selective triazine ligands were adsorbed onto Amberlite XAD-7, then characterised and tested for Am/Eu selectivity, complexation kinetics and polymer loading. These polymers were tested with complex matrices in conjunction with AG1-X8 anion exchange chromatography to achieve a complete isotope separation and quantification method. From these results, the resin capacity factor (KD) as a function of HNO3 concentration was calculated, allowing potential separation methods to be designed. Selective americium extractants from the BTPhen ligand family have been identified through this work, and we also report a study of functionalisation of BTPhen ligands to help design new selective Am extractants by determining the effects on solubilities and americium extraction capabilities of variations in substituents. The data obtained show trends that could assist in future ligand design.

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