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Expanding the Fundamental Chemistry of Thorium Through the Synthesis and Reactivity of the First Molecular Complexes of Th(II) and New Classes of Th(III) and Th(IV) Compounds

  • Author(s): Langeslay, Ryan Richard;
  • Advisor(s): Evans, Willaim J;
  • et al.

This dissertation describes synthetic investigations aimed to expand the fundamental chemistry of thorium. Chapter 1 describes the radical reactivity of thorium-ligand bonds with the molecular radical 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO). Organothorium bonds are found to be very reactive with TEMPO and reveal previously unobserved reaction pathways for thorium. Chapter 2 discusses the isolation and characterization the first molecular complexes which contain thorium in the formal +2 oxidation state: [K(2.2.2-cryptand)]{[C5H3(SiMe3)2]3Th} and [K(18-crown-6)(THF)2]{[C5H3(SiMe3)2]3Th}. Physical, spectroscopic, and theoretical studies of these new Th2+ ions conclude they the first examples of a [Rn]6d2 electronic ground state in an isolable metal complex of any kind. The 6d2 configuration is what is expected for the radioactive fourth row transition metal ions such as Rf 2+ and Db3+. Chapters 3 and 4 describe the reactivity of the new Th2+ complexes, with comparisons to the analogous Th3+ compounds where appropriate. Substrates investigated include H2, [Et3NH][BPh4], cyclooctatetraene, iodomethane, iodoethane, benzyl bromide, chlorbenzene, fluoropentane, and benzyl isocyanide. Th2+ is shown to affect both one- and two-electron reductions of substrates. The isolation of new Th3+ complexes, including the first mixed-valent thorium complex and first hydride of Th3+, [K(18-crown-6)(Et2O)]{[C5H3(SiMe3)2)2ThH2]}2, is described, as well as evidence for the in situ generation of a transient Th2+ complex with the (C5Me4H)33− ligand set. Chapter 5 involves the synthesis and reactivity of the sterically-crowded Th3+ complex (C5Me5)3Th. Other sterically-crowded Th4+ complexes are also isolated and their reactivity is reported. Substrates examined include iodomethane, diiodide, chlorobenzene, trimethylaluminum, dihydrogen, and carbon monoxide. Investigations with carbon monoxide led to the formation of [(C5Me5)3Th(CO)][BPh4], the first room temperature stable carbonyl complex of thorium. Chapter 6 describes an initial investigation into the reactivity of the Th3+ complexes (C5Me4H)3Th and [C5H3(SiMe3)2]3Th with nitric oxide (NO). Two structurally different bimetallic complexes are isolated, namely [(C5Me4H)2Th]2(μ-ONNO), and {[C5H3(SiMe3)2]2Th(μ-O)}2. Chapter 7 describes the synthesis of the nitrile-solvated [(C5Me5)2Th(NCR)5][BPh4]2 (R = Me, Ph, tBu) complexes, which are the first examples of linear metallocenes of thorium containing cyclopentadienyl ligands. Chapter 8 presents preliminary results on other synthetic attempts to isolate low-valent thorium compounds. Evidence of transient low-valent species is described and factors leading to the instability are discussed.

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