published_or_final_version / abstract / toc / Chemistry / Doctoral / Doctor of Philosophy

Although known since the 1930s, organogold chemistry has been dormant until recently, primarily due to preconceptions about the inertness of gold in transformations. However, this last decade has witnessed the emergence of a Golden Age with the development of a wealth of reports on gold in a plethora of reactions. In recent years, the drive for more atom- and step-economical and environmentally friendly reactions has become a field of intense research. In our on-going research on well-defined transition metal complexes bearing NHC ligands, our group recently discovered a new gold(I) hydroxide complex [Au(OH)(IPr)] (1a) that can be easily synthesised from the chloride precursor [AuCl(IPr)] (1b). A preliminary survey of the reactivity of this gold synthon has demonstrated interesting reactivity that holds great potential in bond activation reactions and the development of useful synthetic methods. Simplistically, this gold hydroxide complex can be seen as a strong Brønsted base. This thesis is dedicated to an in-depth examination of the reactivity of this complex in base-free bond activation reactions. Two themes predominate in the following chapters: the first part demonstrates the activity of gold(I) hydroxide as a bond activation agent to readily and efficiently access organogold complexes while the second part studies the reactivity of this compound in decarboxylation processes with carboxylic acids. Chapter 2 and 3 were dedicated to the development of new synthetic routes to access organogold complexes via base-free transmetalation reactions with organoborons and silanes using 1a. The combination of experimental and computational studies allowed identification and isolation of key intermediates in these reactions. Chapter 4 can be seen as a transition between the development of novel methodologies to synthesise aryl and heteroarylgold complexes and the first steps of gold hydroxide 1a as mediator in decarboxylation reaction. As a result, a novel mode of reactivity for gold was discovered and the synthetic route developed constitutes one of the greenest procedures to prepare organogold complexes with the generation of water and CO₂ as only side products. Chapter 5 and 6 venture further into the exploration of 1a in decarboxylation reactions and detail the development of a catalytic process for the protodecarboxylation reaction and subsequent mechanistic investigations of this reaction through stoichiometric experiments and kinetic and computational studies.

No description available.

This thesis presents an investigation into the synthesis of metal complexes of (Nheterocyclic carbene)-based cyclophanes. There were three main areas of focus: synthesis and complexation of bis(4,5-dihydroimidazolium) salts; the synthesis and complexation of phenol-functionalised imidazolium cyclophanes; and the synthesis and complexation of (N-heterocyclic carbene)-based cyclophanes by C-C bond activation of biimidazolium salts with electron-rich metals. The synthesis of xylyl-linked bis(4,5-dihydroimidazolium) salts was investigated. Attempts to prepare these compounds by the cyclisation of a tetraamine (linear or macrocyclic) were unsuccessful due difficulties in preparing the tetraamines. The target compounds could be prepared by adapting the methods developed for the synthesis of bis(imidazolium) salts however problems associated with purification and stability of the products prevented complexation studies. A series of phenol-, phenoxide- and anisole-functionalised imidazolium cyclophanes were prepared. Their structural properties were investigated using dynamic nmr studies and X-ray crystallography. Complexation of the functionalised cyclophanes was investigated. The phenol cyclophane I formed a dinuclear complex with mercury(II). This complex is the first example of a complex derived from a phenol-functionalised imidazolium cyclophane. However the anisole cyclophane II and the unsymmetrical phenol/ortho cyclophane III were unable to form complexes possibly due to steric hindrance and instability of the cyclophane respectively. Preliminary complexation studies of the bis(imidazolium)phenol V suggested that complexation with palladium(II) and mercury(II) were possible but more work is required to determine the optimum reaction conditions. A series of biimidazolium salts VI (both new and known) were prepared. Previously reported biimidazolium salts have very low solubility in common solvents therefore the incorporation of long alkyl chains to the bridging group was investigated as a means to improve the solubility. The structure of the salts was explored using a range of techniques including dynamic nmr spectroscopy, cyclic voltammetry, UV/Visible spectroscopy, X-ray crystallography and mass spectrometry. Some of the biimidazolium salts were able to rotate about the C2-C2' bond and the free energy of activation for this process was estimated using dynamic nmr studies. C-C bond activation of the biimidazolium salts with palladium(0) was used to form a series of palladium(II) complexes (VII) of (NHC)-based cyclophanes. These reactions are the first examples of the synthesis of bis(NHC) complexes by C-C bond activation. The reactivity of the biimidazolium salts with palladium(0) was compared to their solution structure and it was found that only the biimidazolium that were able to rotate about the C2-C2' bond could react with palladium(0).

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

The design, synthesis, characterization, and applications of annulated bis(imidazolium) salts are described. New synthetic methodologies have been developed that allow access to a broad structural range of bis(imidazolium) salts. Initial studies focused on thee use of bis(imidazolium) salts as comonomers in the formation of mainchain organometallic polymers. Two distinct polymer scaffolds were synthesized, one featuring metal(II)dihalides in the main-chain, and the other featuring a chelated metal center. Ultimately, polymerizations were conducted under ambient atmosphere, proceeded in excellent overall yield, and provided main-chain organometallic polymers comprising Ni(II), Pd(II), and Pt(II) with molecular weights up to 106 Da. Departing polymer studies, focus was shifted toward the study of the physical and photophysical properties of the bis(imidazolium) salts. In few synthetic manipulations, a series of highly photoluminescent bis(imidazolium) salts were prepared whose substituents enable emission in solution, in the solid-state, and, uniquely, as free-flowing liquids. Importantly, these materials display excellent physical properties, such as low glass-transition temperatures (< 0 °C) and high thermal stabilities (> 300 °C). In addition, the bis(imidazolium) platform enabled access to two new fluorescent ionic liquid crystals, demonstrating an ability to also control mesomorphic properties of these materials. Further investigations were conducted regarding the photophysical properties of bis(imidazolium) salts. Focus was placed upon absorption and emission wavelength tunability, solvatochromism, red-edge excitation, and chemical stability. Through functional group modulation, the [lambda]em were varied from 329 -- 561 nm with [Phi]fs up to 0.91. Both the absorption and emission characteristics were found to display strong solventdependencies which were found to be strongly influenced by the nature of the bis(imidazolium) core. The red-edge effect was investigated for a series of bis(imidazolium) salts and was found to be similar between Br and BF4 salts, but distinctly different when MeSO4 anions were incorporated. The stability of an amphiphilic BBI was quantified in aqueous solutions of varying pH and > 85% of the emission intensity was retained after 2 h at pH levels of 3 -- 9.

published_or_final_version / abstract / toc / Chemistry / Doctoral / Doctor of Philosophy

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 440-459).

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.