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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Synthesis, Structures, and Reactivity of Zinc, Cadmium, and Magnesium Complexes Supported by Nitrogen Donor and Carboxylate Ligands

Shlian, Daniel January 2022 (has links)
The bis(2-pyridylthio)methyl ligand, [Bptm], offers a synthetically convenient alternative to a variety of multidentate ligands, including most notably [Tptm] (tris(2-pyridylthio)methyl) and [BptmSTol] (bis(2-pyridylthio)(p-tolylthio)methyl), and, in contrast with [Tptm], necessarily coordinates to metal centers in a κ³ fashion. As such, numerous [Bptm] complexes of zinc have been synthesized and structurally characterized. In Chapter 1, we describe the reaction of the protonated ligand [Bptm]H with the homoleptic zinc compounds Me₂Zn and Zn[N(SiMe₃)₂]₂ to afford, respectively, [Bptm]ZnMe and [Bptm]ZnN(SiMe₃)₂; the latter has been used as a starting point for a wide range of reactivity.Most notably, the terminal zinc hydride, [Bptm]ZnH, can be accessed via either (i) metathesis of the zinc siloxide, [Bptm]ZnOSiPh₃, with either PhSiH₃ or HBpin, or (ii) direct metathesis of the zinc amide [Bptm]ZnN(SiMe₃)₂ with HBpin; the latter reactivity is not precedented and offers a novel approach for the synthesis of molecular zinc hydrides. Both [Bptm]ZnN(SiMe₃)2 and [Bptm]ZnH provide access to a variety of monomeric derivatives, including the zinc halides [Bptm]ZnX (X = Cl, Br, I) and the zinc isocyanate [Bptm]ZnNCO; the latter can be accessed directly via (i) metathesis of [Bptm]ZnH with Me₃SiNCO or (ii) a multistep reaction of [Bptm]ZnN(SiMe₃)₂ with CO₂. [Bptm]ZnH also undergoes insertion of CO₂ into its Zn—H bond to afford the zinc formate, [Bptm]ZnO₂CH, in which the formate moiety exhibits a monodentate binding mode in the solid state. This reactivity enables it to serve as a catalyst for the hydrofunctionalization of CO₂; specifically, [Bptm]ZnH catalyzes the hydrosilylation of CO₂ by (RO)₃SiH (R = Me, Et) at elevated temperatures to afford the respective silyl formates (RO)3SiO₂CH, as well as the hydroboration of CO₂ by HBpin at room temperature to afford the boryl formate HCO₂Bpin. In the absence of CO₂, [Bptm]ZnH also catalyzes the reduction of HCO₂Bpin to the methanol level, MeOBpin. Similarly, [Bptm]ZnH serves as an effective catalyst for the hydrosilylation and hydroboration of a variety of ketones and aldehydes. In all cases, hydroboration is more facile than the corresponding hydrosilylation. The [Bptm]Zn system has been investigated computationally, and the kinetics of insertion of CO₂ into the Zn—H bond of [Bptm]ZnH as well as the thermodynamics of the catalytic cycle have been examined. Further mechanistic studies examine two noteworthy spectroscopic features of the system, namely rapid exchange (i) between the zinc and boryl formates [Bptm]ZnO₂CH and HCO₂Bpin, as well as (ii) between [Bptm]ZnH and [Bptm]ZnO₂CH. Both of these exchange processes have been investigated with variable-temperature NMR spectroscopy; in particular, the former exchange resolves at low temperatures and can be confirmed by exchange spectroscopy. In addition to the aforementioned monomeric zinc halides [Bptm]ZnX (X = Cl, Br, I), the dimeric bridging zinc fluoride {[Bptm]Zn(μ-F)}₂ has been synthesized via reaction of Me3SnF with either [Bptm]ZnN(SiMe₃)₂ or [Bptm]ZnH, as outlined in Chapter 2. The dimeric nature of the fluoride in contrast with the other monomeric halides can be attributed to the significant polarity of the Zn—F bond. {[Bptm]Zn(μ-F)}2 also reacts with Me₃SiCF₃ to afford an unusual instance of a structurally characterized zinc trifluoromethyl complex, [Bptm]ZnCF₃. Chapter 3 discusses cadmium analogues to the [Bptm]Zn system, which provide a comparison and a contrast both with their zinc counterparts as well as with previously reported [Tptm]Cd complexes. While the cadmium amide [Bptm]CdN(SiMe₃)2 may be synthesized in a manner corresponding to that for its zinc analogue, the siloxides {[Bptm]Zn(μ-OSiR₃)}₂ (R = Me, Ph) form dimers that are distinct from the monomeric [Bptm]ZnOSiPh₃ and [Tptm]CdOSiPh₃, although similar to {[Tptm]Cd(μ-OSiMe₃)}₂. The distinctions between the [Bptm]Zn and [Bptm]Cd siloxides have been investigated computationally, indicating that the cadmium species show a thermodynamic preference for dimer formation, which can be attributed to the larger atomic radius of cadmium relative to zinc. Attempts to synthesize a cadmium hydride are interrupted by a Schlenk-type equilibrium giving way to the bis(ligand) complex [Bptm]2Cd and CdH₂, which in turn decomposes to Cd and H2. However, spectroscopic studies indicate that under CO₂, [Bptm]CdN(SiMe₃)₂ and HBpin react to trap a cadmium hydride species as the bridging formate derivative, [Bptm]Cd(μ-O₂CH)₂Bpin. The interaction of nitrogen-rich ligands with main group metals is further probed in Chapter 4, which describes the investigation of the coordination of 2,2’:6,2”-terpyridine (terpy) to magnesium compounds. Most prominently, unsubsituted terpy forms an adduct, terpyMg[N(SiMe₃)₂]₂, with the monomeric form of the magnesium amide {Mg[N(SiMe₃)₂]₂}₂. The adduct reacts with halide donors to form a series of mixed amide-halide complexes, terpyMg[N(SiMe₃)]X (X = Cl, Br, I), as well as a mixed amide-azide complex, terpyMg[N(SiMe₃)₂]N₃. These complexes represent the first instances of neutral monomeric terpyMg compounds that feature unsubstituted terpyridine. Structural comparisons of these complexes with one another as well as with comparable compounds are undertaken. Complexes of terpy with cadmium and zinc analogues, terpyCd[N(SiMe₃)₂]₂ and terpyZn [N(SiMe₃)₂]₂, are explored further, and DFT calculations are used to explore the strength of the interactions between the ligand and the metals in each case. Finally, in Chapter 5, attention is given to the recently reported zinc bromide complex featuring a zwitterionic carboxylate ligand, (Cbp)2ZnBr₂. The structure reported for this complex features several anomalous features, including abnormally long Zn—Br and Zn—O bonds, unusually small atomic displacement parameters for Zn, and a high R-value. This information led us to synthesize and investigate the cadmium counterpart, (Cbp)₂CdBr₂; we find that the cadmium complex possesses nearly identical structural parameters to the reported zinc complex, and when the cadmium is refined as zinc, the displacement parameter problems are reproduced. Therefore, we conclude that the reported structure is in fact that of (Cbp)₂CdBr₂, and report a revised structure for (Cbp)₂ZnBr₂.
12

Atom economical and environmentally benign metal catalysed synthesis

Van Der Waals, Dominic January 2014 (has links)
The use of inexpensive metal catalysts for a range of acylation reactions including the activation of anhydrides and the aminolysis of esters. Discussion on the use of a heterogeneous copper catalyst for teh reduction of a range of organic functional groups and its use in amination of nitriles.
13

First-principles study of MgSiO₃ at core-mantle boundary conditions. / 鎂矽酸鹽(MgSiO₃)在核幔邊界條件下的第一性原理研究 / First-principles study of MgSiO₃ at core-mantle boundary conditions. / Mei xi suan yan (MgSiO₃) zai he man bian jie tiao jian xia de di yi xing yuan li yan jiu

January 2008 (has links)
Sung, Siu Chung = 鎂矽酸鹽(MgSiO₃)在核幔邊界條件下的第一性原理研究 / 宋紹聰. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (p. 110-115). / Abstracts in English and Chinese. / Sung, Siu Chung = Mei xi suan yan (MgSiO₃) zai he man bian jie tiao jian xia de di yi xing yuan li yan jiu / Song Shaocong. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Review on MgSiO3 --- p.5 / Chapter 2.1 --- Interior of the Earth --- p.5 / Chapter 2.1.1 --- The importance of MgSiO3 in geosciences --- p.6 / Chapter 2.1.2 --- "Anomalies in lower mantle, D"" layer and the core-mantle boundary" --- p.7 / Chapter 2.2 --- Review on experimental and theoretical studies on MgSiO3 --- p.9 / Chapter 2.2.1 --- The perovskite structure --- p.9 / Chapter 2.2.2 --- MgSiO3 pv --- p.12 / Chapter 2.3 --- ppv structure --- p.14 / Chapter 2.3.1 --- MgSiO3 ppv --- p.15 / Chapter 2.3.2 --- MgSiO3 liquid --- p.18 / Chapter 3 --- Physical quantities in geoscience and molecular dynamics sim- ulations --- p.20 / Chapter 3.1 --- Equation of state --- p.21 / Chapter 3.2 --- Gruneisen parameter --- p.22 / Chapter 3.3 --- Thermoelasticity --- p.22 / Chapter 3.4 --- Phase transition --- p.24 / Chapter 3.5 --- Correlation function --- p.25 / Chapter 3.5.1 --- Pair Distribution function --- p.25 / Chapter 3.5.2 --- Coordination number --- p.27 / Chapter 3.5.3 --- Time correlation function and mean square displacement --- p.27 / Chapter 3.6 --- Seismic velocities --- p.28 / Chapter 4 --- Theoretical Methods --- p.30 / Chapter 4.1 --- Density Functional Theory --- p.30 / Chapter 4.2 --- Approximating exchange-correlation energy functional --- p.33 / Chapter 4.3 --- Car-Parrinello Molecular Dynamics --- p.34 / Chapter 4.4 --- Variable cell dynamics --- p.36 / Chapter 4.5 --- Nose-Hoover Thermostat --- p.37 / Chapter 5 --- Simulation method and details --- p.39 / Chapter 5.1 --- Structure at 0 K --- p.40 / Chapter 5.1.1 --- Initialization of simulation cells --- p.40 / Chapter 5.1.2 --- Convergence test --- p.41 / Chapter 5.1.3 --- "Electronic minimization, fictitious electronic mass and time step" --- p.42 / Chapter 5.2 --- Electronic and ionic minimization --- p.43 / Chapter 5.3 --- Cell optimization and structure at 0 K --- p.44 / Chapter 5.3.1 --- Optimized simulation cell of pv and ppv --- p.44 / Chapter 5.4 --- Equation of state and stability of solid --- p.46 / Chapter 5.5 --- Melting --- p.48 / Chapter 5.6 --- Statistical average --- p.50 / Chapter 6 --- MgSiO3 perovskite and post-perovskite at CMB conditions --- p.51 / Chapter 6.1 --- Equations of state of pv and ppv at 0 K --- p.51 / Chapter 6.2 --- Enthalpy of pv and ppv at 0 K --- p.54 / Chapter 6.3 --- Equations of state of pv and ppv at different temperatures --- p.55 / Chapter 6.4 --- Fluctuation of stress components of pv and ppv --- p.59 / Chapter 6.5 --- Pair distribution function of pv and ppv --- p.61 / Chapter 6.5.1 --- Pair distribution function at different temperatures with similar cell volume --- p.61 / Chapter 6.5.2 --- Pair distribution function at 4000 K and different volumes --- p.66 / Chapter 6.5.3 --- Pair distribution function at 6000 K and different volumes --- p.70 / Chapter 6.5.4 --- Coordination numbers --- p.74 / Chapter 7 --- Liquid structure at CMB conditions --- p.78 / Chapter 7.1 --- Equations of state of liquid --- p.78 / Chapter 7.2 --- Stress components of liquid --- p.80 / Chapter 7.3 --- Pair distribution function of liquid --- p.83 / Chapter 7.4 --- Coordination numbers of liquid --- p.88 / Chapter 7.4.1 --- Mean square displacement --- p.88 / Chapter 8 --- Phase diagram of MgSiO3 --- p.92 / Chapter 8.1 --- Pressure-temperature relations --- p.92 / Chapter 8.1.1 --- Enthalpy --- p.94 / Chapter 8.2 --- Internal energy --- p.96 / Chapter 8.3 --- Phase boundaries and phase diagram --- p.99 / Chapter 9 --- Discussions --- p.105 / Chapter 9.1 --- Phase diagram --- p.105 / Chapter 9.2 --- LDA vs GGA --- p.107 / Chapter 9.3 --- Pv and ppv at low pressure --- p.107 / Chapter 9.4 --- Two-phase method --- p.108 / Bibliography --- p.110 / Chapter A --- Rotation and shape optimization --- p.116
14

Microstructural and superconducting properties of V doped MgB2 bulk and wires

Castillo, Oscar Eduardo. Schwartz, Justin, January 2004 (has links)
Thesis (M.S.)--Florida State University, 2004. / Advisor: Dr. Justin Schwartz, Florida State University, College of Engineering, Dept. of Mechanical Engineering. Title and description from dissertation home page (viewed June 17, 2004). Includes bibliographical references.
15

Fabrication of in-situ MgB₂ thin films on Al₂O₃ substrate using off-axis PLD technique

Wu, Yi Sun. January 2007 (has links)
Thesis (M.Sc.-Res.)--University of Wollongong, 2007. / Typescript. Includes bibliographical references.
16

Oxidative dyhydrogenation of propane and butane to olefins using Co(5)MgA/O catalyst

Majoe, Nampe 04 1900 (has links)
Olefins have enjoyed many uses in a wide variety of industries, from car manufacturing to energy production. Energy consuming processes of catalytic dehydrogenation, turning paraffins into olefins, has been commercialised since the early 20th century, while catalytic oxydehydrogenation of paraffins to olefins is still in prototype stages. The conflict between kinetic and thermodynamic yield constraints, has delayed the commercialisation of this process. The solution to achieving the relevant process route is exploitation of the right catalyst at moderate temperatures and pressures. Co5MgAlO is studied under atmospheric pressure and 350°C temperature, to dehydrogenate propane and butane to olefins using oxygen as a reactant. Thermodynamic models showing how many reaction routes are possible under atmospheric pressure were explored. Experimental results for butane to air at ratio of 1:0.8 and 1:1.2 hydrocarbons to air gave better selectivity of 1-butene which was more than 12%. When compared with propane at similar reaction ratios the reaction favoured CO2 at selectivity of more than 95%. / Civil and Chemical Engineering / M.Tech. (Chemical Engineering)

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