Dissertation
Synthesis of organometallic tantalum indenyl and thorium guanidinate complexes
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Autumn 2024
DOI: 10.25820/etd.007556
Abstract
Metal complexes, particularly those in unique coordination environments, have been known to display a high degree of reactivity, often with small molecules of energy relevance. In an interest to expand that reactivity, three research projects were undertaken: the synthesis of the first permethylindenyl complex of the Group 5 metals, -heptamethylindenyltantalum tetrachloride (Ind*TaCl4), and its spectroscopic, electrochemical, and reduction chemistry to compare with known tantalum-pentamethylcyclopentadienyl complexes; the use of potentially dinucleating ligands: 3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate (hpp), its tetramethylated analogue (hpp*), and 2,3,5,6-tetrahydro-1H-imidazo[1,2-a]imidazolate (tbo-) in reactions with thorium(IV) and the attempted synthesis of a highly-novel dinucleating ligand featuring two fused six-membered rings in a conjoined di-N-heterocyclic dicarbene, a neutral cousin to bicyclic guanidinate ligands.
Chapter 1 introduces the reactivity of metal complexes with small molecules relevant to environmental sustainability and energy production. Chapter 2 is a review of transition metal compounds featuring homometallic bonding and their reactivity, and π-bound organometallics of niobium and tantalum from 2005 to August 2020. Chapter 3 begins the original research conducted by the author, namely with the synthesis and study of the first permethylindenyl complex of the Group 5 metals, the blue, four-legged piano stool Ind*TaCl4. Its synthesis, spectroscopy, electrochemistry, and solid-state structure are described. Its surprisingly substantial max red-shift by UV-vis spectroscopy, when compared to that of luminescent yellow Cp*TaCl4, is explained by time-dependent DFT. TD-DFT calculations predict very-close values of the max for both compounds and explains this red-shift in terms of a lowering of the HOMO-LUMO gap for Ind*TaCl4 compared to Cp*TaCl4. The reduction products and their reactivity are then probed briefly. Chapter 4 details the synthesis of four new thorium guanidinate molecules, two molecular and mononuclear [Th(hpp*)Br3(THF)2 and Th(hpp*)4], and two mononuclear salts [(hpp*(SiMe3)2]2[ThBr6] and [tbo(SiMe3)2]2[ThBr6], and their structural characterizations. Comparisons to analogous uranium chemistry are made. Chapter 5 gives an overview of the various routes attempted to synthesize a di-NHC ligand, theoretically a good candidate for the dinucleation of two zirconium atoms and their potential bonding. While numerous and varied routes were investigated, the compound remains elusive, as the syntheses become unviable, or led to unanticipated products. Chapter 6 provides a conclusion as well as future outlook for the research discussed within this thesis.
Details
- Title: Subtitle
- Synthesis of organometallic tantalum indenyl and thorium guanidinate complexes
- Creators
- Grant Emerson P. Forsythe
- Contributors
- Louis Messerle (Advisor)F. Christopher Pigge (Committee Member)Scott R. Daly (Committee Member)Scott K. Shaw (Committee Member)Gregory K. Friestad (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Chemistry
- Date degree season
- Autumn 2024
- DOI
- 10.25820/etd.007556
- Publisher
- University of Iowa
- Number of pages
- xviii, 201 pages
- Copyright
- Copyright 2024 Grant Emerson P. Forsythe
- Language
- English
- Date submitted
- 12/08/2024
- Description illustrations
- Illustrations, tables, graphs, charts
- Description bibliographic
- Includes bibliographical references (pages 186-201).
- Public Abstract (ETD)
A great societal goal is the increase in efficiency of chemical processes that contribute to human well-being, but also in a serious way to climate change, usually through the generation of the energy required to perform difficult chemical reactions. One such example is the Haber-Bosch process, a means of producing ammonia for fertilizers from dinitrogen and hydrogen that consumes ~2% of the energy used annually. The reason for the great consumption in the Haber-Bosch and other processes is the energy cost incurred in breaking very strong chemical bonds, e.g. the nitrogen-nitrogen triple bond. In previous work, the Messerle research group has been able to synthesize small molecules containing unique coordination environments, particularly a ditantalum core with two bonds between the tantalum atoms. These molecules react cleanly with small molecules of energy importance, like dinitrogen, at room temperature and at pressures not exceeding 100 psi. Indeed, many examples of organometallic complexes have shown varied and remarkable reactivity towards small molecules, easily cleaving apart otherwise difficult chemical bonds.
The work to follow describes three projects aimed at the discovery of new organometallic complexes with potentially promising reactivity, particularly from a member of the fourth group of transition metals and thorium, and the synthesis of a new tantalum-tantalum dinuclear molecule for comparison with those already known. Two new tantalum molecules, four new thorium molecules, and a variety of new organic molecules were synthesized, and subjected to spectroscopic and X-ray crystallographic investigations in order to determine their structures and chemical properties, and some initial studies of reactivity are reported.
- Academic Unit
- Chemistry
- Record Identifier
- 9984774664402771