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<p> This dissertation is based on the hydro(solvo)thermal syntheses and characterization of uranyl (UO₂²⁺) coordination polymers (CPs) via single-crystal X-ray diffraction (SC-XRD), powder X-ray diffraction (PXRD), and luminescence spectroscopy. The rich structural portfolio of uranyl CPs arises from the UO₂²⁺ cation&rsquo;s tendency to undergo hydrolysis, and form uranyl oligomeric species (or secondary building units, SBUs). Because of hydrolysis, synthetic control of SBUs is difficult and more often then not, their solid-state crystallization is random and unpredictable. Thus, it is challenging to know what building unit will be observed in a uranyl CP. </p><p> Our strategy to address such challenges and potentially thwart hydrolysis is to use N-donor chelating ligands. These ligands offer potential chelating sites that may allow for direct coordination to UO₂²⁺ and thus essentially promote specific uranyl building units. The N-donor ligands chosen in our study are 2,2&rsquo;:6,2&rdquo;-terpyridine (TPY), analogs of 2,2&rsquo;-bipyridine (BPY), 2,4,6-tripyridyl-s-triazine (TPTZ), and 2,3,5,6-tetrakis(2-pyridyl)pyrazine (TPPZ). By restricting UO₂²⁺ speciation, assembly of aromatic or aliphatic O-donor linkers to available coordination sites on UO₂²⁺ allowed us to synthesize a series of uranyl CPs containing N-donor (TPY, TPTZ, BPY analogs) and O-donor co-ligands. These coordination polymers resulted in extended structures with unique structural topologies and luminescent features. </p><p> Depending on the choice of N- and O-donors, structural variations in the local UO₂²⁺ coordination sphere and global structure within a uranyl CP were observed. N-donor chelating ligands were also explored as guest molecules, in which a series of CPs containing TPTZ, BPY analogs, or TPPZ and different O-donor aliphatic or aromatic linkers were synthesized. These guests were found to stabilize the structure through non-covalent interactions or participate as charge balancing species. Beyond structural manipulation of our materials, we also studied UO₂²⁺ luminescence and lifetimes within our uranyl CPs. We observe that modifications on either the N- or O-donor (i.e. sterics, functional groups, and/or non-covalent interactions) or a change in the local and global structure of a CP influences UO₂²⁺ luminescence thus resulting in unique spectral signatures. </p><p> Given the influence of N-donors and O-donors on the structure and luminescence of an uranyl CP, we also explored the synthesis of uranyl complexes using N-donor BPY, 5,5&rsquo;-dimethyl-2,2&rsquo;-bipyridine (MeBPY), and TPY ligands exclusively via self assembly conditions in the presence of sunlight and ambient light. Unexpectedly, we observe the presence of peroxo ligands in our crystal structures. To explore the origin of the peroxo ligand, rigorous synthetic experiments were performed in which the presence of peroxo most likely arises from a mechanism consistent to photo-excitation of UO₂²⁺.</p>

<p> This dissertation describes the synthesis of a series of transition metal compounds and their reactivity with hydrogen and carbon dioxide for application in reversible hydrogen storage in organic molecules. Chapter 1 is a review of hydrogen storage molecules and discusses each from the perspectives of safety, availability, and environmental impact. Heterogeneous and homogeneous catalysts for dehydrogenation of these molecules are also discussed here. In Chapter 2, a family of PNP pincer-supported iron compounds is investigated by M&ouml;ssbauer spectroscopy and magnetic circular dichroism with the goal of elucidating the degree of solution-state flexibility of the PNP pincer ligand. Chapter 3 expands on this family of PNP pincer-supported iron compounds with the synthesis of several new compounds through reaction with hydrogen and carbon dioxide. Furthermore, these compounds are shown to be highly active catalysts for formic acid dehydrogenation in the presence of a Lewis acid co-catalyst. The action of the Lewis acid co-catalyst is further demonstrated in Chapter 4, where PNP pincer-supported iron compounds are used as catalysts for aqueous-phase methanol dehydrogenation. Chapter 5 describes the synthesis, characterization and reactivity of a family of palladium and nickel compounds supported by allyl, cyclopentadienyl, and indenyl ligands. These compounds are shown to react with simple electrophiles, although they do not show the desired reactivity with carbon dioxide.</p>

A new electron-transport material using a triarylboron-functionalized 2,4,6-triphenyltriazine core has been synthesized. This compound exhibits reversible reduction with low-lying HOMO and LUMO energy levels, as well as a high-energy triplet state. Preliminary experiments incorporating this material into phosphorescent OLEDs as an electron transport layer gave devices with high current and external quantum efficiencies at brightness levels appropriate for applications in the display industry. Furthermore, a nitrogen-containing alkynyltriarylboron compound, 2-(2’-(dimesitylboryl)phenylethynyl)pyridine, has been found to undergo a facile alkyne hydration reaction in the presence of copper(I) iodide and triethylamine. The copper(I)-catalyzed addition of water occurs at room temperature, and produces a brightly luminescent boron-enol compound that is stable under air. Studies of the reaction mechanism were carried out by monitoring product formation under different conditions using 1H NMR. The cooperativity between the Lewis acidic triarylboryl group and Lewis basic pyridyl group is determined to be vital in promoting the hydration process and in stabilizing the enol structure of the product. Finally, we have discovered that diarylplatinum(II) complexes of 2-(2’-(dimesitylboryl)phenylethynyl)pyridine are capable of undergoing an unusual intramolecular double aryl migration/cyclization reaction, resulting in the formation of a unique bicyclic organometallic scaffold. The structures of these remarkable products have been characterized by X-ray crystallography, as well as by 1D and 2D 1H NMR. The reaction mechanism was established by 1H NMR studies and by DFT calculations. The complementary electronic properties of the electron-deficient triarylborane and the electron-rich platinum centers were found to play a key role in this unprecedented transformation. / Thesis (Master, Chemistry) -- Queen's University, 2012-06-20 10:24:39.074

abstract: ABSTRACT Transition metals have been extensively employed to address various challenges related to catalytic organic transformations, small molecule activation, and energy storage over the last few decades. Inspired by recent catalytic advances mediated by redox noninnocent pyridine diimine (PDI) and α-diimine (DI) ligand supported transition metals, our group has designed new PDI and DI ligands by modifying the imine substituents to feature donor atoms. My doctoral research is focused on the development of PDI and DI ligand supported low valent first row metal complexes (Mn, Fe, Co) and their application in bond activation reactions and the hydrofunctionalization of unsaturated bonds. First two chapters of this dissertation are centered on the synthesis and application of redox non-innocent ligand supported low valent iron complexes. Notably, reduction of a DI-based iron dibromide led to the formation of a low valent iron dinitrogen compound. This compound was found to undergo a sequential C-H and C-P bond activation processes upon heating to form a dimeric compound. The plausible mechanism for dimer formation is also described here. Inspired by the excellent carbonyl hydrosilylation activity of our previously reported Mn catalyst, (Ph2PPrPDI)Mn, attempts were made to synthesize second generation Mn catalyst, which is described in the third chapter. Reduction of (PyEtPDI)MnCl2 furnished a deprotonated backbone methyl group containing Mn compound [(PyEtPDEA)Mn] whereas reduction of (Ph2PEtPDI)MnCl2 produced a dimeric compound, [(Ph2PEtPDI)Mn]2. Both compounds were characterized by NMR spectroscopy and XRD analysis. Hydrosilylation of aldehydes and ketones have been studied using [(PyEtPDEA)Mn] as a pre-catalyst. Similarly, 14 different aldehydes and 6 different ii formates were successfully hydrosilylated using [(Ph2PEtPDI)Mn]2 as a pre-catalyst. Encouraged by the limited number of cobalt catalysts for nitrile hydroboration, we sought to develop a cobalt catalyst that is active for hydroboration under mild conditions, which is discussed in the last chapter. Treatment of (PyEtPDI)CoCl2 with excess NaEt3BH furnished a diamagnetic Co(I) complex [(PyEtPDIH)Co], which exhibits a reduced imine functionality. Having this compound characterized, a broad substrate scope for both nitriles and imines have been investigated. The operative mechanism for nitrile dihydroboration has been investigated based on the outcomes of a series of stoichiometric reactions using NMR spectroscopy. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2018

<p> Several solvothermal synthetic methods have been developed to produce novel low-dimensional magnetic materials and determine their structure-properties relationships. Two main classes of compounds were investigated, including iron selenides and transition metal formate-chlorides.</p><p> Chapter 2 details the development of the first solution-based synthetic route to superconducting iron (II) selenide. Samples were found to retain superconducting properties only when air and water were rigorously excluded from the synthesis.</p><p> Chapter 3 presents the synthesis, structure, and magnetic properties of two new mixed-valence compounds with infinite &infin;¹(FeSe₂) tetrahedral chains separated by Fe-amine complexes. The use of different Fe-amine complexes allows for tuning of the magnetic properties without changing the general structural motif.</p><p> Chapters 4 and 5 report the first members of the transition metal chloride-formate family of compounds, which contain linear zig-zag chains of octahedrally coordinated metal atoms linked by &mu;₂-Cl and <i>syn-syn</i> formate bridges. These compounds order antiferromagnetically and exhibit metamagnetic transitions.</p><p> Chapter 6 describes a related set of transition metal formate-chloride compounds that are comprised of helical chains of edge-sharing M²⁺-centered octahedra. These compounds undergo 3D ferrimagnetic ordering at low temperature, and are rare examples of homospin topological ferrimagnets. </p><p>

Interprotein electron transfer (ET) is crucial for natural energy conversion and a fundamental reaction in the pursuit of understanding the broader problem of protein-protein interactions and reactivity. Simplifying the complicated nature of these natural systems has driven development of biomimetic approaches. Functionalized gold nanoparticles offer simplified, tunable surfaces that can serve as a proxy to study the reactivity and dynamics of proteins. Amino-acid functionalized gold nanoparticles (Au-TX) served as a complementary partner to cytochrome c (Cyt c) and catalyzed its ET reactivity without altering the native structure. Redox mediator and EPR experiments confirmed that the redox potential and coordination environment of the heme were unaltered. Varying the functionality of Au-TX under limiting redox reagent concentrations resulted in distinct ET reactivity. These conditions reflected the collision of a small redox reagent with the Cyt c/Au-TX adduct, introducing the possibility of Cyt c/Au-TX dynamics to modulate ET. Under high ionic strength conditions, the rate enhancement ranged from 0.0870 × 1011 for Cyt c/Au-TAsp to 1.95 × 1011 M-1 s-1 for Cyt c/Au-TPhe. Au-TAsp binds to a larger surface of the front face of Cyt c than Au-TPhe, likely reducing heme access and resulting in attenuated ET reactivity. Site-directed spin-labeling characterized the dynamic interactions and motion of Cyt c with Au-TX. Several mutants of Cyt c were utilized to extract information about the different dynamics of the Cyt c/Au-TPhe and Cyt c/Au-TAsp systems. Cyt c appeared to have a highly dynamic binding interaction with the surface of Au-TPhe while binding to Au-TAsp resulted in a more rigid interface, particularly at the heme crevice. The dynamic interaction of Cyt c/ Au-TX at the heme crevice could promote a gated ET mechanism between Cyt c and its redox partner. Thus, the reduced reactivity of Cyt c/Au-TAsp is likely a result of both slower global dynamics and more rigid binding near the heme crevice.

This research aims to optimize the synthesis of oriented inorganic semiconductor nanostructures through templated electrodeposition. Specifically, the thesis focused on cadmium selenide and cadmium telluride. The electrodepostion conditions were first optimized using nickel, gold or indium tin oxide as the electrode. These conditions were then used to deposit within the pores of polycarbonate or anodic aluminum oxide membranes to yield nanorods or nanotubes. The nanostructure synthesis was further extended to segmented nanorod or coaxial nanorod structures by addition an extra deposition cycle. The realization of these structures through electrodeposition adds a valuable tool in the synthetic tool box for the synthesis of semiconductor nanostructures for solar cells. In the other part of my research, the mechanism of copper-catalyzed cross coupling reactions was probed through chemical kinetics. The results obtained were not consistent with the normally proposed mechanistic path - oxidative elimination.