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Some cyclic trans-vicinal di-secondary thiols have been synthesised in high yields by reduction of the corresponding trithiocarbonates with lithium aluminium hydride. Various approaches to the synthesis of tetrahydrofuran-trans-31 4-dithiol, sulpholane-trans- 3,4-dithiol and indane-trans-1,2-dithiol were investigated, but without success. Further evidence on the course of acetyl migration during the alkaline hydrolysis of trans-2-acetylthiocyclopentanol has been obtained. Quantitative alkaline deacetylation of this compound in the presence of a competitive acceptor confirms the original proposal by Harding and Owen that acetyl migration is intramolecular. A crucial test was performed in which cyclopentene sulphide was prepared in 75% yield from trans-2-mercaptocyclopentyl acetate, which, according to the present theory, is the direct precursor of the episuiphide. Some cyclic trans-vicinal hydroxy-thiols have been synthesised via the corresponding epoxides. A number of isopropylidene derivatives and cyclic carbonates were prepared under mild conditions from the ABSTRACT (cont.) various dithiols and hydroxy-thiols. Some of,these derivatives provide further examples of compounds containing the highly strained system in which two five-membered rings are transfused. Kinetic investigations were made to study the formation of the isopropylidene derivatives by the acid catalysed condensation of acetone with the appropriate dithiols and hydroxy-thiols. A method has been developed in which the progress of the reaction is followed by the disappearance of the thiol value of the mercapto compound. It has been shown that in a large excess of acetone the rate is first-order with respect to thiol, and that it varies approximately with the square of the catalyst concentration. The mechanism proposed by Ross for this type of reaction is discussed and critisized, and a modified mechanism is proposed.

Whilst Group 2 elements continue to emerge from their obscurity, with a plethora of heterofunctionalisation thus described, such extensive investigations into cross metathesis, remain limited. Described herein is an extensive investigation into a variety of factors which contribute to the understanding of the complexity of the mechanistic surface upon which Group 2 mediated catalytic cross- and stoichiometric σ-bond-metatheses sit. An initial study into the synthetic potential of σ-bond metathesis yielded a range of unprecedented and structurally fascinating compounds- mixed metal amidoalkyls and amidohydrides of Groups 1 and 2. Subsequently, a pair of variables in Group 2 mediated dehydrocoupling was investigated: a) The effect of congeneric variation upon Group 2 (magnesium, calcium and strontium) mediated dehydrocoupling of amines and silanes, most notably indicating the significance of ancillary ligation, solution molecularity and precatalyst activation mechanisms. b) The effect of variation in hydridic coupling partner on the dehydrocoupling of a range of amines with 9-BBN, pinacol(borane) and diphenylsilane mediated by a β-diketiminate supported magnesium centre, most notably indicating the profound effect of coupling partner Lewis acidity and contingent variations in catalyst molecularity and rate determining step. Finally, an investigation into the introduction of unprecedented steps in Group 2 catalysis is reported herein. Specifically, the activity of the stable radical TEMPO is investigated for its propensity to induce single electron transfer upon labile, reactive ligands around magnesium and the ability for its anionic analogue to undergo σ-bond metathesis.

The aim of work described in this thesis is to gain insight into the role of interfaces on atomic transport processes in polycrystalline uranium dioxide at high temperatures. Previous studies have highlighted the importance of grain boundaries as fast diffusion pathways and their potential to significantly effect the oxidation of nuclear fuel samples. The effect of interfacial transport is also significant in terms of helium produced through the α-decay of actinides throughout the life-cycle of nuclear fuels. The resultant swelling can have important implications for the long term storage of nuclear materials and can even lead to radionuclide release. Chapter 1 comprises a review of the relevant literature focussing on the uranium oxide system, oxide microstructure and the transport properties of both helium and oxygen. In Chapter 2 the computational methodologies used throughout this investigation are described in detail including both energy minimisation and molecular dynamics. Chapter 3 focuses on the development of a new potential for uranium dioxide derived to be computationally efficient and suitable for large simulation cells. Additionally the model needed to be capable of modelling the high temperature structures of tilt and twist grain boundaries and accurately representing oxygen transport. Having developed and validated the model, we explored protocols for generating grain boundaries and in Chapters 4 and 5 model a range of tilt and twist grain boundaries. In each case the structure, stability and transport properties of each were investigated in depth. Chapter 6 introduces a new helium potential model and uses it to evaluate the diffusion and segregation in a range of tilt grain boundaries. Also introduced is a new type of interface that models the interface where grain boundaries and surfaces meet. The approach of routinely generating such interfaces is explored and is then applied to look at the release of helium from bulk UO2 to the gas phase. The thesis concludes in Chapter 8 with a summary of the thesis and possible direction of future work.

The aim of this thesis is to investigate the synthetic utility of insertion reactions with Group two complexes, specifically towards the activation of the small molecular gas; carbon monoxide. Extension of this Group two mediated reactivity into catalytic regimes exploits both σ–bond metathesis and insertion chemistries with hydride sources such as PhSiH3 or HBpin to generate value added chemicals. Chapter Two demonstrates organoisocyanates are readily converted to methyl amines through hydrodeoxygenation with HBpin in the presence of the β–diketiminato magnesium catalyst, Ib. A series of catalytically relevant species have been identified and fully characterized through stoichiometric reactivity studies. These data suggest that overall reduction and C–O activation occur through the intermediacy of well–defined magnesium formamidato and magnesium boryloxide species. This reaction is further explored through a DFT study which complements the experimental findings. Chapter Three explores the reaction between both β–diketiminato magnesium, Ih, and calcium, Ii, hydride complexes with carbon monoxide, resulting in the isolation of dimeric cis–enediolate species by the reductive coupling of two CO molecules. Under catalytic conditions with PhSiH3, an observable magnesium formyl species may be intercepted for the mild reductive cleavage of the CO triple bond to a methane analogue in the case of Ih. The related calcium formyl species could not be identified but under identical catalytic conditions reduced CO to a methoxysilane species, demonstrating the variability in the chemistries of the group two elements. Chapter Four investigates the carbonylation of a range of in situ generated β–diketiminato Ae–NRRʹ (Ae = Mg or Ca, R = H or Me and Rʹ = H, Alkyl or aryl) complexes, resulting in the isolation of a number of formamidate complexes and including a carbenic formamide dimagnesium species. The hydrodeoxygenation chemistry that was explored in Chapter Two is then extended to the range of isolated compounds providing a novel route to methyl amines.

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