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Structural determinations and electrochemical properties in the series of multinuclear ferrocenyl-ethynyl complexes with formula [(£b5-C5(CH3)5)(P2)MII-C¡ÝC-(fc)n-C¡ÝC-MII(P2)(£b5-C5(CH3)5)] (fc = ferrocenyl; M = Fe(II), Ru(II), Os(II); R = H, CH3; P2 = Ph2PCH2CH2PPh2 (dppe)) are reported. Complexes with more electron-rich ligand environment, were prepared with regard to the understanding of electronic coupling mechanism. These complexes undergo sequential reversible oxidation events from -0.2 V to 1.0 V referred to the Ag/AgCl electrode in anhydrous CH2Cl2 solution and the low-pontential waves have been assigned to the end-capped metallic centers. The magnitude of the electronic coupling between two terminal metallic centers in the series of complexes was estimated by electrochemical technique. Based on the correlation between the £GE1/2 values and the second redox potentials of the end-capping metallic centers in the series of complexes, a qualitative explanation for the different magnitude of the electronic coupling is given.

The design, synthesis, characterization and application of carbene-based metallopolymers are described herein. Metallopolymers have found wide applications in the fields of photovoltaics, energy storage and electrochromic windows. The incorporation of N-heterocyclic carbene (NHC) functionalities into a polymerizable scaffold would allow for many different metals to be attached in a facile and high-yielding manner. Such complexes could be functionalized onto surfaces and utilized as either spectroscopic or antimicrobial devices. Early attempts in our lab focused on utilizing bis(thiophene) diimines (instead of NHCs) as scaffolds for metal chelation and polymerization. This approach was unsuccessful due to the lability of the diimine moiety under electrochemical cycling and the thiophene moieties were not able to undergo polymerization. In order to more fully understand the key transformation in synthesizing the thiophene-substituted diimines, a comprehensive investigation of the aldimine coupling transformation was undertaken. A high concentration of substrate and catalyst was determined to be the most important factor in obtaining high yields of the dimerized products. Green solvents such as acetonitrile and hexanes could be used for the dimerization reaction when the cyanide counteranion was changed from sodium to tetrabutylammonium. The steric limitations were systematically identified and a series of possible substrates have been ruled out as viable candidates for dimerization. Applying the experience gleaned from earlier reports, the first example of an NHC polymer was prepared in which the monomer features an NHC functional group orthogonally connected to its main chain. A polymerizable imidazolylidene-AuCl complex containing pendant bithiophene moieties was prepared by a high yielding, multistep procedure. Oxidative electropolymerization of this monomer afforded the desired polymer (Au[NHC]Cl)n, which was characterized on the basis of electrochemical studies as well as by X-ray crystallography, photoelectron and UV-vis spectroscopy. The methodology described above was expanded to develop a series of analogous poly(N-heterocyclic carbene) complexes with appended entities (M = Ir, Au, Ag, or S)and found to be electrochromic. Most of the polymers exhibit an intense absorbance wave at 700 nm under oxidative conditions which is attributable to the formation of polaron excitations along the polymer main chain. The presence of a transition metal significantly increased the electrochromic character of the polycarbene system. The iridium-containing polymer was found to possess significant near-infrared (NIR) absorbance at 1100 nm in which the metal moiety effectively functions as an electron sink. Electrochemical analysis of the polymer thin films revealed that they exhibit highly reversible electrochromic activities. / text

Graduate

Corpus Christi Bay in Texas is a wind driven system, and under most conditions winds over the bay mix the water column vertically. However, seasonal, episodic, bottom-water hypoxia has been observed in the bay in conjunction with vertical salinity stratification. This stratification may be caused by dense gravity currents entering the bay. Understanding and modeling the mechanisms that result in stratification in Corpus Christi Bay may help predict hypoxia, and for this reason that is the focus of this dissertation. An evaluation of existing gravity current modeling techniques shows that most currently available models are designed to capture either phenomena local to a gravity current, such as gravity current entrainment and spreading, or larger scale phenomena such as wind mixing and large-scale circulation, but not both. Because gravity current mixing in Corpus Christi Bay is enhanced by wind-induced turbulence, both local gravity current physics and wind mixing effects are critical elements governing gravity current propagation in Corpus Christi Bay. As existing models do not represent gravity current entrainment and wind mixing together, this dissertation develops a coupled model system that accounts explicitly for turbulent wind mixing of a bottom-boundary layer, in addition to representing other local features of dense gravity current propagation such as entrainment and spreading. The coupled model system consists of a 2D depth-averaged hydrodynamic model that calculates gravity current mixing and spreading, coupled with a 3D hydrodynamic model whose domain includes a lighter ambient fluid surrounding the gravity current. The coupled models have flexible boundary conditions that allow fluid exchange to represent mixing from both gravity current entrainment and wind mixing. The coupled model system’s development, verification and application in Corpus Christi Bay advances understanding of gravity current mechanisms, and contributes to our scientific understanding of hypoxia in Corpus Christi Bay. This modeling technique has the flexibility to be applied to other density-stratified systems that are shallow and potentially wind-driven, such as shallow desalination brine disposal sites. / text

No description available.

In this dissertation we consider several limiting criteria forn-dimensional diffusion processes defined as solutions of stochasticdifferential equations. Our main interest is in criteria for polynomialand exponential rates of convergence to the steady state distributionin the total variation norm. Resulting criteria should place assumptionsonly on the coefficients of the elliptic differentialoperator governing the diffusion.Coupling of Harris chains is one of the main methods employed in thisdissertation.

Enormous efforts have been made to optimize the Pd-catalyzed Suzuki-Miyaura reaction, but there is to date no generally useful protocol and forcing conditions are often required. One reaction variable that has often been neglected is the extent to which the supposed catalysts, bisphosphinepalladium(0) complexes, are actually formed from the variety of popular precatalysts used. There is in fact little evidence that these precursors produce bis-ligated Pd(0) complexes and it is possible that the rate limiting factor may be catalyst formation. If so, then the development of an optimized method for forming these catalytic species would be a significant contribution to this field. The following work describes research efforts to determine the optimum conditions to generate PdL2 (L = PCy3, PMeBut2, PBut3) cleanly and quantitatively from Pd(3-C3H5)(5-C5H5) and Pd(3-1-Ph-C3H5)(5-C5H5). Furthermore, the conditions under which PdL3 species may exist in equilibrium with the PdL2 species are defined. NMR studies indicate that while Pd(PBut3)2 shows no inclination to increase its coordination number, Pd(PCy3)2 and Pd(PMeBut2)2 react with added phosphine to form 3:1 compounds. Equilibrium constants for dissociation of the PdL3 compounds were measured over a range of temperatures, yielding the thermodynamic parameters of dissociation and estimated Pd-P bond dissociation energies. Additionally, the generation of heteroleptic species serve to confirm the existence of 3:1 compounds. A kinetic study of the oxidative addition of PhBr to Pd(PCy3)2 was also performed. It was found that oxidative addition was first order in palladium, but that added bromide had no effect on the rate of oxidative addition. Added PCy3 inhibited oxidative addition, possibly due to the conversion of palladium(0) into the less active 3:1 compound. The formation of the catalytically less active 3:1 compounds has serious implications for many catalytic cross-coupling processes which involve catalyst formation via the slow reduction of palladium(II) in the presence of excess phosphine; for many systems, relatively little of the added palladium may actually be present as the active bisphosphinepalladium(0) compound. / Thesis (Ph.D, Chemistry) -- Queen's University, 2008-12-08 13:24:50.825

The primary focus of the research is to extend the principles of Nanofiltration(NF) to non-aqueous systems using solvent-resistant NF membranes. Several differentlevels of interaction are introduced when organic solvents are used with polymericmembranes and thus quantification of polymer-solvent interactions is critical. Puresolvent permeation studies were conducted to understand the mechanism of solventtransport through polymeric membranes. Different membrane materials (hydrophilic andhydrophobic) as well as different solvents (polar and non-polar) were used for the study.For example, hexane flux at 13 bar through a hydrophobic silicone based NF membranewas ~ 0.6 x 10-4 cm3/cm2. s. and that through a hydrophilic aromatic polyamide based NFmembrane was ~ 6 x 10-4 cm3/cm2. s. A simple model based on a solution-diffusionapproach which uses solvent physical properties (molar volume, viscosity) andmembrane properties (surface energy, etc) is used for correlating the pure solventpermeation through hydrophobic polymeric membranes.Solute transport studies were performed using organic dyes and triglycerides inpolar and non-polar solvents. For example, the rejection of Sudan IV (384 MW organicdye) in n-hexane medium is about 25 % at 15 bar and that in methanol is about –10 % atabout 20 bar for a hydrophobic (PDMS-based) membrane. However, for a hydrophilicpolyamide based NF membrane, the direction of separation is reversed (86 % in methanoland 43 % in n-hexane). From our experimental data with two types of membranes it isclear that coupling of the solute and solvent fluxes cannot be neglected. Two traditionaltransport theories (Spiegler-Kedem and Surface Force-Pore Flow model) that considercoupling were evaluated with literature and our experimental solute permeation data. Amodel based on a fundamental chemical potential gradient approach has been proposedfor explaining solute separation. The model uses solute, solvent and membrane physicalproperties and uses the Flory-Huggins and UNIFAC theories as activity coefficientmodels. This model has been used to obtain a correlation for the diffusion coefficients ofsolutes in hexane through a hydrophobic membrane. This correlation along withconvective coupling can be used to predict separation behavior for different solutes and atdifferent temperatures.

A series of substituted indoles have been synthesized by the sequential reaction of aromatic aldehydes with ethyl azidoacetate in the presence of sodium ethoxide to form the corresponding ethyl α-azido-β-arylacrylates (Knoevenagel process) followed by a solvent mediated thermolysis (Hemetsberger process). The isolated yields of the ethyl α-azido-β-arylacrylates were significantly increased when employing the sacrificial electrophile ethyl trifluoroacetate. 1H NMR and coupled 1H-13C NMR analysis of the ethyl α-azido-β-arylacrylates indicate that the condensation is stereospecific—only the Z-isomer could be detected. Solvent mediated thermal treatment of the meta-substituted ethyl α-azido-β-arylacrylates resulted in the formation of both the 5- and 7- substituted indoles—the 5-regioisomer being slightly favored over the 7-regioisomer. Analogous thermal treatment of (2Z, 2Z’)-diethyl 3,3’-(1,3-phenylene)bis(2-azidoacrylate) and (2Z, 2Z’)-diethyl 3,3’-(1,4-phenylene)bis(2-azidoacrylate) exclusively produced pyrroloindoles, diethyl 1,5-dihydropyrrolo[2,3-f]indole-2,6-dicarboxylate and diethyl 1,5-dihydropyrrolo[2,3-f]indole-2,6-dicarboxylate, respectively. Results are also reported which indicate that the α-azido-β-arylacrylates can be used in the subsequent Hemetsberger indolization process without prior purification. Organic substrates containing basic nitrogen centers have been problematic in achieving high yields in the Suzuki coupling process. The origin of this issue is attributed to the complexation of the basic nitrogen center with the palladium catalyst. As a consequence, the use of CO₂ at a variety of pressures was evaluated as a reversible protecting/activating reagent for basic nitrogen containing substrates. The following observations and conclusions were reached. (1) The use of small amounts of water significantly improves the rate and yield of Suzuki coupling reactions. (2) In the presence of aqueous CO₂, careful selection of the base is essential due to formation of bicarbonate and the associated decrease in the amount water. K3PO4 was found to be the most effective base in the presence of CO₂. (3) The yield of product in the Suzuki coupling of 4-amino-2-bromopyridine with phenylboronic acid was evaluated as a function of CO₂ pressure. Compared to reactions in the absence of CO₂, the yield of product increased at all pressures of CO₂ (6.8, 17, and 30.6 atm) - from 15% with no CO₂ to 73% with 30.6 atm of CO₂.