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Title: The chemistry of uranium triamidoamine complexes
Author: Gardner, Benedict Matthew
ISNI:       0000 0004 2747 1283
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2012
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With the ever-diminishing reserves of fossil fuels, it is inevitable that nuclear power will represent a major source for global energy production in the not too distant future. The principal nuclear fuel, uranium, interacts with numerous other elements from all over the Periodic Table during its life in the nuclear energy cycle. A more profound appreciation of the chemical behaviour of uranium and its compounds represents a significant and important link in the chain towards the development of better nuclear fuel materials and cleaner long-term waste treatment solutions. However, the f-block elements and especially the actinides - of which uranium is one - are generally far less researched than all other areas of the Periodic Table; so much so that uranium chemistry is conservatively estimated to be thirty to forty years behind that of the transition metals. In view of the major developments in the understanding of chemical structure and bonding that have resulted historically from the exploration of metal-metal bonds, studying the nature of such interactions between uranium and unconventional metal-based ligands - as opposed to its more traditional bonding partners - represents an excellent opportunity to further our understanding of the chemistry accessible to one of the least studied groups of elements in the Periodic Table. In addition, investigations into uranium complexes that can activate important industrial feedstock materials such as molecular nitrogen (N2) and carbon monoxide (CO) - a feat which, generally, can be very difficult to achieve - has undergone significant development in recent years with a view to finding an alternative to dwindling resources of crude oil. A range of new organometallic uranium complexes that feature the tripodal TrenR triamidoamine ligand [TrenR = {N(CH2CH2NR)3}3-, R = SiMe3, SiMe21Bu] have been prepared. These include halide, triflate, amide, alkyl, ion pair and diazoalkane derivatives, representing valuable precursors for a range of non-aqueous uranium chemistry including cyclometallation, metal-metal bond formation, photochemistry and redox activity. Additionally, remarkable uranium-mediated double dearylation chemistry of the tetraphenylborate anion was observed for the first time with a novel reactive dinuclear Tren-uranium alkyl complex. The first definitive examples of unsupported uranium-transition metal bonds are presented in the form of the heterobimetallic U-Re complexes [U(TrenR)(ReCp2)] which have been subject to a iii combined experimental and computational analysis. Theoretical studies revealed the presence of both (J- and n-interactions to the metal-metal bonds, although the degree of covalency was found to be modest. This was proceeded by the synthesis of the U-Ru systems [U(TrenR){RuCp(CO)2}], which are the first complexes known to contain uranium-ruthenium bonds and ab initio calculations revealed the uranium-ruthenium interactions to be entirely electrostatic in nature. It has been demonstrated that a Tren-uranium(ITI) complex can selectively achieve the reductive homologation of Cl-carbon monoxide under mild conditions to C2- ethynediolate, (C202/-. Following treatment with organosilyl halides, the functionalised acetylenes RMe2SiOC=COSiMe2R (R = Ph, Me) underwent conversion to Ca-furanones upon liberation with the direct precursor to the active trivalent species formed concurrently, thus closing the synthetic cycle. A computational study suggested that this uniquely straightforward liberation chemistry is a result of the sterically demanding, inflexible and preorganised nature of the Tren- uranium unit, revealing the potential for uranium-mediated catalytic homologation of CO into higher-order industrially relevant derivatives such as petrochemical feedstocks, fine chemicals and pharmaceuticals.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available