Pericyclic reactions are a class of transformations that comprise sigmatropic rearrangements, group transfer reactions, cycloadditions and electrocyclic reactions. Since Woodward and Hoffmann rationalized the mechanism and stereochemistry of pericyclic reactions they have become powerful synthetic tools. Whilst sigmatropic rearrangements and cycloadditions are cornerstones of contemporary synthetic methodology, many electrocyclic reactions are not fully exploited currently; there are no general methods for the asymmetric catalysis of electrocyclic reactions and as a consequence, opportunities for exerting stereocontrol in these manifolds are limited. We aim to establish general methods for the asymmetric catalysis of 6π electrocyclic reactions. Our initial studies are focused on a pentadienyl anion moiety due to the greater ease of cyclization observed with such systems in comparison to the corresponding neutral hexatriene systems.

<p>Catalysis has a responsibility to provide solutions to the growing grand challenge of sustainability in the fuels and chemical industry to help combat climate change. These changes; however, cannot be realized without a more fundamental understanding of the active sites that catalyze chemical reactions, and how they can be tuned to control rates and selectivities. Four specific examples of active site modification will be considered in this work: the speciation of isolated metals in zeolite frameworks, solvent thermodynamics and structure at defects in zeolite frameworks, the electronic modification of platinum through alloying in well-defined intermetallic nanoparticles, and the mobility and shape of gold nanoparticles in zeolite channels. Each will highlight how quantum chemistry calculations can provide a fundamental understanding of how these active site modifications influence the kinetics of chemical reactions, and how they can be controlled to pursue solutions to the reduction of carbon through sustainable utilization of shale gas as well as renewable chemicals production through biomass upgrading.</p> <p>Zeolites exchanged with metal heteroatoms can behave as solid Lewis or Br<a>ø</a>nsted acids depending on heteroatom identity. Lewis acid heteroatoms can adsorb water and hydrolyze to speciate into “open sites” which have been shown to differ in their ability to catalyze reactions such as glucose isomerization as compared to “closed sites” which are fully coordinated to the zeolite framework. The structure and catalytic properties of these sites are interrogated by a gas phase reaction, ethanol dehydration, in Sn-Beta by a combined Density Functional Theory (DFT) and experimental study. DFT is used to map the possible reaction mechanisms for ethanol dehydration, including the speciation of Sn sites into hydrolyzed configurations from water or ethanol. A microkinetic model for ethanol dehydration including unselective and inhibitory intermediates is constructed. This microkinetic model predicts the population of reactants and products on the catalyst surface as well as the sensitivity of individual elementary steps to the total rates. Powerful anharmonic entropy methods using <i>ab-initio </i>molecular dynamics (AIMD) is used to capture the entropy of confined reactive intermediates, which is shown to be necessary to compare with experiment. Results on closed and hydrolyzed open zeolite sites can then be compared with ethanol dehydration on “defect open” sites which were shown experimentally to occur at material stacking faults. A grain boundary model is constructed of zeolite Beta, where unique sites have similar ligand identity as hydrolyzed open sites. These defect open sites are found to not contribute to the observed reaction rate as they cannot stabilize the same transition state structures that were observed in internal Beta sites. </p> <p>Intuition about the ethanol dehydration reaction in Sn-Beta was then used to map a more expansive and diverse chemical network, the synthesis of butadiene from acetaldehyde and ethanol. For elementary reactions in this mechanism, which included aldol condensation, MPV reduction, and crotyl alcohol dehydration in addition to ethanol dehydration, the hydrolyzed open sites were found to be crucial reactive intermediates. Hydrolyzed sites were necessary to stabilize favorable transition states, which requires reconstruction of the local framework environment. Methods to preferentially stabilize hydrolyzed sites were then explored, using a screening algorithm developed to consider all possible sites in each zeolite framework. It was found that the stability of these hydrolyzed sites could be correlated to the local strain exerted by the surrounding silica matrix. This provides a new descriptor that stabilizes intermediates relevant to the synthesis of butadiene and ethanol dehydration.</p> <p>Next, the structure and thermodynamic stability of water networks around Sn-Beta defects and heteroatom active sites was considered using AIMD. As many biomass reactions occur in the presence of water, the interactions of water with hydrophobic and hydrophilic functionalized defects dictate how the stability of reactive intermediates and transition states is affected by a solvating environment. Locally stable and strongly nucleated clusters of water were observed to form at Sn defects, with less densely packed water structures stable at hydrophilic defects. This is in comparison to defect-free siliceous Beta, where significantly less water uptake is observed. These local clusters are in equilibrium with the less dense liquid-like phase that extends between defects. These results motivate localized cluster models around active sites in Lewis acids, as well as advance the fundamental understanding of hydrophobic/hydrophilic interactions in microporous materials. The local cluster models are then applied to the ethanol dehydration reaction in protonated aluminum Beta zeolites where experimentally observed non-unity coefficient ratios are rationalized by quantifying a different degree of solvation for the ethanol reactant state as opposed to the transition state, validated by a thermodynamic phase diagram.</p> <p>Changes in the electronic energy levels of <i>d</i> electrons upon alloying was studied in conjunction with a new spectroscopic technique being performed at Argonne National Laboratory to develop new descriptors to predict the degree of coking for different alloys. Resonant Inelastic X-ray Scattering (RIXS) simultaneously probes the occupied and unoccupied valence states of platinum in nanoparticles at ambient conditions. The specific excitation process of this spectroscopy is particularly amendable to DFT modeling, which was used to provide richer chemical insight into how changes in observed RIXS signature related to the electronic structure changes of platinum upon alloying. From a suite of multiple 3d alloy promoter catalysts synthesized, a quantitative comparison with DFT modeled spectroscopy was developed. The stability of DFT calculated coke precursors, relevant to dehydrogenation catalysts to convert light alkanes into olefins, was then correlated to DFT modeled RIXS spectra, which is a better descriptor for adsorption of unsaturated chemical intermediates that used previously, as well as being a descriptor accessible to direct experimental usage.</p> <p>Finally, the diffusion of gold nanoparticles in the TS-1 catalyst was studied using AIMD to help understand what structural motifs of gold are present under reaction conditions and how the shape and binding sites of gold is strongly influenced by deformation by the zeolite framework. This is used to help predict new zeolites for use in direct propylene epoxidation using molecular oxygen and hydrogen. The optimization of this catalyst is environmentally relevant to reduce the usage of inorganics and reduce the cost associated with production of hydrogen peroxide. Following these discussions, the role of computation in the prediction of active site structures and kinetics in conjunction with experiment was included. The broader impact of these findings will also be considered, which span beyond these specific reactions and materials.</p>

Catalysis allows for the controlled formation of new bonds, whilst reducing both time and energy expenditure in the process. Catalysis has traditionally been the realm of precious metals, which have been used to carry out a bewildering array of reactions. However, there is an ever-increasing drive for the development of catalytic methodology employing sustainable and environmentally benign catalysts. Two such candidates are organocatalysis, omitting the need for metals where possible, or the use of iron catalysis. Two key areas to the advancement of the of field catalysis are the identification and development of new catalysts as well as an understanding of the mechanisms of established catalytic processes. Novel catalysts can provide many benefits such as enhanced or even novel reactivity, access to new classes of substrates or simply be more readily accessible compared with previously developed catalysts. To this end, the first example of Lewis-base-catalysis using the recently developed cyclopropenimine motif is reported. This was exploited in the trifluoromethylation of aldehydes and ketones using the Rupert-Prakash reagent (Scheme A-1). Scheme A-1 Cyclopropenimine-catalysed trifluoromethylation of aldehydes and ketones Developing an understanding of catalytic methodologies in the terms of their mechanism and active species is also a key area in catalysis. Insight into these can direct the expansion of these systems in terms of both more effective catalysts and tailoring reaction conditions as examples. The iron-catalysed hydromagnesiation of styrene derivatives was studied in detail. This culminated in a proposed mechanism, involving a novel hydride transfer process (Scheme A-2). Studies were carried out using a combination of kinetic analysis and in situ Mössbauer spectroscopy, as well as successfully isolating and studying the reactivity of a catalytically-relevant, formal iron(0)-species.

This Thesis is concerned with the synthesis of post-metallocene group 4 amidinate complexes as pre-catalysts for the polymerisation and oligomerisation of α-olefins. Activation of half-sandwich group 4 amidinate complexes with 1,3-conjugated dienes is also investigated and their underlying chemistry is explored. <strong>Chapter 1</strong> introduces homogeneous Ziegler-Natta catalysis, with a specific focus on group 4 compounds. A review of metallocene and post-metallocene complexes of group 4 will also be presented and their behaviour in olefin polymerisation will be discussed. <strong>Chapter 2</strong> describes the synthesis and characterisation of _K1-amidinate supported titanium complexes. Base-free activation of the titanium cyclopentadienyl-amidinate dialkyl complexes will be investigated and the resulting cationic species will be further explored with commonly applied trapping agents. The synthesis and characterisation of new titanium cyclopentadienyl-amidinate diene complexes and their corresponding tri(pentafluorophenyl)borane-activated zwitterionic compounds will also be described and their performance in the co-polymerisation of ethylene and propylene will be discussed. <strong>Chapter 3</strong> explores the addition of 1,3-conjugated diene reagents to titanium cyclopentadienyl-amidinate and guanidinate alkyl cations. Mechanistic and computational studies of allyl and diene formation will also be described. The polymerisation capabilities of the newly formed complex will be discussed and compared to previously reported dialkyl complexes. <strong>Chapter 4</strong> describes the synthesis and characterisation of aminopyridinato titanium complexes and _K1-_K2-bis(amidinate) titanium complexes. The activation chemistry of the newly formed dialkyl complexes will be investigated. Furthermore, the synthesis of a new bis(aminopyridinato) titanium complex will also be discussed alongside their activity in EPM and EPDM polymerisation. <strong>Chapter 5</strong> describes the performance of the aminopyridinato titanium complexes (synthesised in Chapter 4) in EPDM polymerisation. The sensitivity of the aforementioned complexes towards hindered phenols will also be discussed and their behaviour in ethylene oligomerisation will be explored. <strong>Chapter 6</strong> presents full experimental procedures and characterising data for the new complexes reported in this Thesis.

Alkaline degradation of Carbaryl in the presence of CTAB micelles has been reported as the most efficient method; however, the factors accounting for it are not yet clear. The main objective of this work was to study some of the factors affecting the alkaline degradation of Carbaryl in the presence of cetyl trimethylammonium bromide (CTAB). Three specific aims were researched in order to address the main objective. Solubility studies, UV-vis, fluorescence, and 1D-HNMR and 2D-HNMR spectroscopies were used to research the solubilization of carbaryl in CTAB micelles. Solubility studies showed that carbaryl partitions into CTAB micelles with a binding constant of 553 ± 8 M-1, and each mole of micellized surfactant incorporates about 0.336 moles of carbaryl. Spectroscopy studies showed that carbaryl does not interact electrostatically with micelles but does through van der Waals interactions. 1D-HNMR and 2D-HNMR indicated solubilization in the Stern layer, oriented with its hydrophilic moiety towards the Goüy-Chapman layer and the hydrophobic moiety towards the core of the micelle. Kinetic studies as a function of the surfactant concentration along with micellar kinetic models were used to calculate micellar rate constants (k’M) for each of four different cationic surfactants: cetyl trimethylammonium hydroxide (CTAOH), cetyl trimethylammonium bromide (CTAB), cetyl trimethylammonium chloride (CTACl), and cetyl pyridinium chloride (CPCl), and compared to the corresponding rate constants (k’W) in water; the results in all cases showed k’M / k’W > 1. This fact led to the conclusion that additional factors beyond solubilization of substrates are playing a role. Solubility studies revealed the following binding constant order and solubilization capacity order: CPCl > CTAOH ≈ CTAB > CTACl, CPCl > CTAOH ≈ CTAC > CTAB, indicating that for CPCl, Coulombic interactions, such as charge-transfer complexes, may be favoring the concentration effects, while for other surfactants, such as CTAOH, the [–OH] as the micelle counterion increases Carbaryl’s concentration in the Stern layer compared to its bulk concentration. In contrast, large, weakly-hydrated polarizable ions such as Br– displace hydrophilic ions, providing less enhancement. Kinetic experiments as a function of the surfactant head’s charge led to the conclusion that cationic and zwitterionic surfactants have a catalytic effect of the alkaline hydrolysis of carbaryl, while nonionic and anionic surfactants have inhibitory effects: kobs (cationic) > kobs (zwitterionic) > kobs(nonionic) > kobs (anionic). A similar order for solubility parameters (Ks and SC) was observed from equilibrium solubility studies. Experiments as a function of the polarity of the medium in the presence of both polar and nonpolar solvents showed that the hydrolysis rate is inversely proportional to the medium polarity. Ionic strength experiments showed that the hydrolysis rate is inversely proportional to the ion concentration.

La catálisis es un campo de la ciencia que explora soluciones a los problemas ambientales como la contaminación, la eliminación de los residuos generados en el proceso de síntesis de materiales o la regeneración de los recursos naturales. En la presente Tesis, hemos reportado un estudio de cálculos DFT para la σ activación del enlace NH de amoníaco considerando las especies μ3-alquilidinos de titanio utilizando el complejo modelo [{Ti(η5-C5H5)(μ-O)}3(μ3-CH)]. Posteriormente, con el fin de analizar la hidroformilación asimétrica de estireno catalizada por complejos Rh-Binaphos, se han combinando estudios basados en la aproximación de la determinación del estado de transición y un análisis cualitativo a través de un descriptor molecular recién definido (volumen de distancia ponderada, VW). Usando nuestro conocimiento mecanicista anterior, hemos presentado un estudio QSPR para predecir la actividad y la enantioselectividad de la hidroformilación de estireno catalizada por complejos Rh-difosfinas. También, hemos desarrollado una nueva metodología 3D-QSSR para predecir la enantioselectividad basada en la cuantificación de la representación de diagramas por cuadrantes y aplicándola en el ciclopropanación asimétrica de alquenos catalizadas por complejos de cobre. / Catalysis is a field of science that explores solutions to environmental problems such as pollution, elimination of waste generated in the process of materials synthesis or regeneration of natural resources. In the present Thesis, we have reported a DFT study on the N-H σ-bond activation of ammonia by the µ3-alkylidyne titanium species using the [{Ti(η5-C5H5)(µ-O)}3(µ3-CH)] model complex. Afterwards, we have combined the TS-based approach and qualitative analysis through a newly defined molecular descriptor (distance-weighted volume, VW), in order to analyze the asymmetric hydroformylation of styrene catalyzed by Rh-binaphos complexes. Using our previous mechanistic knowledge, we have presented a QSPR study to predict the activity and the enantioselectivity in the hydroformylation of styrene catalyzed by Rh-diphosphane complexes. We have also developed a new methodology to predict enantioselectivity based on the quantitative quadrant-diagram representation of the catalysts and 3D-QSSR modeling; and we have applied it in the asymmetric cyclopropanation of alkenes catalyzed by copper complexes.

Since the discovery of Wilkinson’s catalyst and its usefulness in the homogeneous hydrogenation of olefins many investigations have been carried out on trivalent, tertiary phosphine–rhodium complexes.¹ Studies have shown that N-Heterocyclic carbenes as ligands offer increased stability to the complex and possess similar electronic properties as phosphine ligands.² The applications of the traditional catalyst are limited due to the limited stability of its solutions and its susceptibility to attack from the environment i.e. oxygen and moisture. The hydrogenation of olefins and other unsaturated compound is of great importance for the fine chemical and petroleum industries. The aim is to produce more stable and active versions of the traditional catalyst and also to demonstrate their improved stability and activity in catalytic applications. This study involves the investigation of the effects of ligand modification on Wilkinson type hydrogenation catalysts. Five Rhodium-phosphine complexes 1a: Rh(PPh₃)₃Cl, 1b: Rh(PPh₂Me)₃Cl, 1c: Rh(PPh₂Et)₃Cl, 1d: Rh(PPhMe₂)₃Cl, 1e: Rh(PPhMe₂)₃Cl have been synthesised and characterised by means of melting point,¹H NMR, ¹³C NMR, ³¹P NMR, IR and Mass Spectroscopy. Complexes 1d and 1e have also been characterised by means of elemental analysis and single crystal XRD. Five rhodium-N-heterocyclic carbene complexes 2a: Rh(COD)ImesCl [Imes =1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] , 2b: Rh(COD)(diisopropylphenyl)₂Cl 2c: Rh(COD)(adamantyl)²Cl, 2d: Rh(COD)(diisopropyl)²Cl 2e: Rh(COD)(ditertbutyl)²Cl have been synthesised and characterised by means of melting point, ¹H NMR, ¹³C NMR, IR and Mass Spectroscopy. Five rhodium-NHC-CO complexes 3a: Rh(CO)₂ImesCl, 3b: Rh(CO)₂(diisopropylphenyl)₂Cl, 3c: Rh(CO)₂(adamantyl)₂Cl , 3d: Rh(CO)₂(diisopropyl)₂Cl, 3e: Rh(CO)₂(ditertbutyl)₂Cl, have been synthesised and characterised by means of ¹H NMR, ¹³C NMR, IR and Mass Spectroscopy. Complexes 1a, 1d, 1e, 2a, 2b, 2c, 2d, 2e were tested in the hydrogenation of simple alkenes under mild conditions. For the rhodium-phosphine complexes the catalyst efficiency based on TOF increases in the following order: 1a > 1d > 1e or RhCl₃(PPhMe₂)₃ > RhCl₃(PPhEt₂)₃ > RhCl(PPh₃)₃. For the rhodium-(COD)-NHC complexes catalyst efficiency based on TOF increases in the following order: 2d > 2b > 2e > 2a > 2c. While rhodium-phosphine complexes are far more active than rhodium-(COD)-NHC complexes, the latter seem to be active for a longer time and hence more stable under mild hydrogenation conditions. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2010.

Os-Zn-Al hydrotalcite-like compounds (HTlc’s) were synthesised by the co-precipitation method and characterised using different techniques (powder XRD, ICP-OES, FT-IR spectroscopy, BET-surface area measurements, SEM and SEM-EDS, cryo-TEM, 27Al SS-NMR and TGA-DSC). The hydrotalcite-like catalyst was used to heterogenise the aminohydroxylation reaction. Among the three solvents investigated (toluene, MeCN/water (1:1 v/v) and t- BuOH/water (1:1 v/v)) in the aminohydroxylation reaction, toluene showed the slowest reaction rate, MeCN/water (1:1 v/v) and t-BuOH/water (1:1 v/v) demonstrated fast reaction rates comparable to each other. The reaction temperature was only significant when toluene was used as the solvent system (reaction time (100% depletion of starting material) and temperature are inversley proportional). The catalyst HTlc structure demonstrated a significant effect in terms of the reaction time and isolated yield of the -amino alcohols. Under the same testing conditions a heat treated catalyst (non-HTlc) showed a shorter reaction time, a reduction in the isolated yield of -amino alcohols with a rise in diol formation. All the different classes of olefins (aliphatic, aromatic, and functionalised) that were tested, gave 99.99% depletion of starting material. However, due to the same purification difficulties encountered in the homogeneous amino hydroxylation (AA) reaction, the isolated yield of -amino alcohols achieved here, ranged from 13 to 35 %, with the highest yield (35%) obtained when methylcinnamate was used as the olefin. Characterisation of the spent catalyst showed that HTlc structure is maintained, but crystallinity was lost (the material becomes polycrystalline) after the reaction. The leaching test showed that 4.5% and 5.5% of Os leached from the catalyst to the reaction solution when MeCN/water (1:1 v/v) and t-BuOH /water (1:1 v/v) were used as the solvent system, respectively. The leached form of Os was determined to be inactive, indicating that this system is truly heterogeneous. The recycling study (three cycles) indicated that the catalyst can be recycled, but with a decrease in the reaction rate (which could be due to structure defects and loss of crystallinity), and with no significant difference in the isolated yield of the amino-alcohol. The crystal structure of three -amino alcohols are also reported. The crystal structure of the - amino alcohol of cyclohexene, methylcinnamte and t-butylcrotonate were needle-like triclinic, pi, needle-like monoclinic, p21/c and cubic-like triclinic, p-1, respectively. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2010.

Copper is an inexpensive, earth-abundant, non-toxic metal that is found to have widespread applications in catalysis. Ullmann and Ullmann-type reactions and Glaser-Hay oxidative coupling of terminal alkynes are some of the well-established copper catalyzed coupling reactions used for the construction of important organic molecules, including pharmaceuticals, commodity chemicals and polymers. Those reactions have been mainly performed homogeneously, where the removal of residual copper from the reaction mixture is a challenge. Therefore, many researchers tried supporting copper precatalysts in order to help recover, and thus reduce final product contamination. Some studies showed that copper leached significantly from the support, with others showing that leached copper has a role in the catalysis. Nevertheless, many studies reported that the used supported catalysts were recyclable and claimed catalyst's heterogeneity. In most cases, the nature of the truly active copper species is still not clear. The objectives of this thesis were (1) to assess the heterogeneity/homogeneity of active copper species in popular catalytic C-N coupling reactions with already studied catalysts, mainly a copper exchanged zeolite and copper oxide nanoparticles, and (2) to use the collected information in designing a truly heterogeneous (stable and recyclable) catalyst. Initially, and because of its shape selectivity characteristics, copper-exchanged NaY zeolite, Cu(II)Y, was chosen to study the heterogeneity of copper catalyzed amination of aryl iodide with imidazole. The collected results from conducted shape selectivity tests indicated that Cu(II)Y might be heterogeneous catalyst, but because of the used base, that is crucial for this C-N coupling reaction, the crystallinity of the zeolite structure was diminished. Therefore, it was important to support copper on a framework that is stable under the basic conditions required for this type of reaction if a heterogeneous, recyclable catalyst were to be achieved. For this purpose, cerium oxide was chosen, and copper oxide supported on cerium oxide, CuO-CeO₂, was investigated as a potential heterogeneous catalyst for C-N coupling reaction. This investigation included the role of each reaction reagent in facilitating copper leaching into solution. It was found that copper leached from the support and it was demonstrated through hot filtration tests that the leached copper species was the main active catalyst. Leaching was caused by the solvent (DMSO) as well as the used reactants and the base. Similar conclusions were drawn when this CuO-CeO₂ catalyst was used for the direct synthesis of imines from amines under aerobic conditions. Although this CuO-CeO₂ catalyst has the advantages of being more recoverable and active than unsupported CuO nanoparticles at similar copper loadings, it is not fully recyclable, as the copper catalysis occurs in solution. These findings meant that designing a truly heterogeneous catalyst for this reaction is a challenging task. Understanding the effect of each individual factor of this complicated system might help in achieving the second goal - designing a truly heterogeneous catalyst. Therefore, further studies were carried out to understand the effect of reaction conditions, including temperature, base, support, and solvent, on copper leaching. Homocoupling of terminal alkynes was chosen as a model reaction for this study, and CuO was supported on TiO₂ (10CuO-TiO₂) and on γ-Al₂O₃ (10CuO-Al₂O₃). It was found that copper interaction with the support affects the extent of leaching as well as the nature and activity of leached species. High temperature also facilitates copper leaching especially when a ligating amine, like piperidine, is present in the system.

Rhodium-catalyzed hydroacylation is a powerful and atom-economical method for synthesizing ketones from aldehydes and olefins. Despite this, a narrow scope of reactive substrates has limited the utility and broad application of this transformation. Efforts towards the development of new classes of reactive substrates have focused on the use of oxygen- and sulfur-containing olefins, which have enabled various modes of reactivity and thus allowed access to novel types of hydroacylation products. In addition to reactivity, a key to the success of these transformations is the control of regio-, stereo-, and chemoselectivity. In combination with substrate structure, strategies in enantioselective catalysis and metal-organic cooperative catalysis have been applied to achieve requisite reactivity and selectivity when required. A variety of products, such as medium-sized heterocycles, branched sulfur-containing and β-hydroxy ketones, and ketones bearing quaternary carbon centres have been synthesized via hydroacylation using these strategies. A method for preparing polyelectrolyte-stabilized palladium nanoparticles and their use in Suzuki coupling reactions have also been developed.