University of Sussex
Nicholls, Laura E..pdf (69.07 MB)

Uranium silicate complexes as models for surface immobilised uranium catalysts

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posted on 2023-06-08, 23:15 authored by Laura E Nicholls
Chapter 1 provides an insight into the current areas of research that could provide answers to the global energy problems outlined in Appendix A, namely the reductive functionalisation of carbon oxides and as an extension to this, the activation of other small molecules. The review predominantly concentrates on the chemistry of the 5f elements which already contain examples of reductive functionalisation of carbon oxides, albeit in homogeneous phase. In addition the chapter provides an overview of the current research in surface science and by extension, the development of molecular models that mimic such surfaces. This synopsis provides an insight into the difficulties involved in this area of research and why molecular mimics are of vital importance. Using ligating Si-O bonds to mimic a silica surface, Chapter 2 outlines the research which enabled the development of a series of uranium siloxides, centred on the previously unreported pentakis(triarylsiloxy) uranate(IV) ion. Characterisation data and full analysis are included within this chapter which provided the basis for the investigations discussed in the following chapters. This chapter also presents an interesting UV-Vis analysis of the uranium siloxides which will enable a wider understanding of the f -elements and the role f -orbitals have on the chemistry and geometry of f -element molecules. Chapter 2 develops a deeper understanding of these complexes by investigating the mechanisms of formation and the chemistry of the U(Ph3SiO)5 fragment using ESI techniques in conjunction with NMR analysis. Chapter 3 investigates the reactivities of the uranium siloxides previously developed and discusses a new dioxo species and a rare and novel UV monooxo complex which was synthesised and successfully isolated. An analysis of other dioxo and monooxo complexes is included which allows the reader to develop an appreciation of how few and far between monooxo products are. In addition, previous examples of monooxo’s are lacking characterisation data and are mostly products of oxygen atom donor reactions, not as a result of small molecule activation as is presented here. There is currently one previous example of such a system resulting from small molecule activation which is also discussed in this chapter. Chapter 4 investigates a second ligand system which could be used to mimic a silica surface. Whilst the ligand, tris tertbutoxy has been investigated previously, at the time of this work, the ligand had not been successfully used in relation to a uranium complex. The U3.5 species, [(U(OSi(OtBu)3)3)2(µ-?6:?6-tol))] is presented here alongside the complexes [((tBuO)3SiO)3U]2(µ2-O)3 and U(OSi(OtBu)3)4. During the development of this species, very similar species were published by another group and these syntheses and characterisation data are presented here as a comparison to the species developed as part of this work. Chapter 5 investigates the reactivities of the uranium siloxides developed in Chapter 4 including decomposition analysis and reactions with small molecules such as O2, I2 and CO2 and presents the resulting complexes some of which were developed by a Masters student working in collaboration with the author.


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