Thesis (M.Tech. in Chemistry)--Tshwane University of Technology, 2011. / Examines the possible factors responsible for catalyst deactivation occurring on nickel and cobalt bimetallic catalysts supported on different carbonaceous materials (i.e. multi-walled carbon nanotubes, activated carbon and graphite).

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Soluble polymers as supports are gaining more attention now. Developing new polymers, new reagents and catalysts, new separation systems are thus of great interest as these sorts of materials' applications in synthesis and catalysis increase. The work described in the succeeding chapters describes my efforts to synthesize new catalysts that can be attached to polymer supports, to study their catalytic activity and to study separation efficiency. Most of the work focus is on polyacrylamide polymers. Both organometallic catalysts and organic catalysts have been studied. Liquid/liquid separation was the technique mainly investigated. In addition, a new separation scheme called latent biphasic system which is a new liquid/liquid separation method is described. Finally, studies with the Cremer group where the LCST behavior of polyacrylamides was studied using dark field methods are also discussed.

The catalytic partial oxidation of methane to produce synthesis gas using a platinum/nickel dual bed reactor has been shown to have high conversions and selectivity of synthesis gas products, hydrogen and carbon monoxide. In this work the relative length of the platinum and nickel in the dual bed reactor is investigated experimentally and a model describing the nickel portion of the dual bed catalyst is developed. The model uses simplified flow conditions, experimentally determined temperature profiles and an elementary reaction mechanism to describe the nickel bed of the reactor. The rate parameters of the elementary reaction in the mechanism are determined using theoretical methods. Unity Bond Index - Quadratic Exponential Potential (UBI-QEP) is used to determine the activation energy and thermodynamic consistency is forced to produce a set of preexponential factors.

El objetivo de este trabajo se centró en la síntesis de nuevos catalizadores homogéneos de paladio para la reacción de copolimerización de monóxido de carbono con estireno. El interés de esta reacción catalítica radica en las propiedades de los copolímeros a que da lugar, que son termoplásticos bio- y fotodegradables. La ventaja de usar catalizadores homogéneos para la copolimerización, respecto a la polimerización radicalaria, es que en los copolímeros obtenidos las moléculas de monóxido de carbono y estireno se encuentran insertadas de una manera perfectamente alternada y regular. Para ello la utilización de precursores organometálicos de paladio(II) que posean un ligando quelato, ha sido descrita como la mejor forma de obtener sistemas activos.La influencia de la naturaleza del ligando quelato en la actividad del precursor catalítico, en especial la de sus átomos dadores, ha llevado a la elección de ligandos bidentados nitrógeno- y azufre-dadores para la realización de este trabajo. Así se ha escogido una serie de ligandos ditioéter, previamente utilizados en otros procesos catalíticos, así como ligandos piridina-pirazol y pirimidina-pirazol para estudiar su efecto sobre el metal y sobre la actividad del catalizador en la reacción de copolimerización. Además con el objeto de hacer un estudio sistemático de la influencia del ligando se ha diseñado y sintetizado una nueva familia de ligandos nitrógeno-dadores piridina-imidazolina de simetría C1. Estos nuevos ligandos piridina-imidazolina poseen la ventaja de ser fácilmente modificables, dando lugar a series de ligandos con variaciones estructurales sistemáticas.La coordinación de todos estos ligandos a paladio ha dado lugar a nuevos complejos neutros de fórmula [PdClMe(L-L)] y catiónicos de fórmula [PdMe(NCMe)(L-L)][X]. El análisis de la estereoquímica de los nuevos complejos sintetizados se realizó por RMN, observándose claras diferencias en función de ligando utilizado. Asimismo en algunos de los casos la obtención de monocristales ha hecho posible el análisis de la estructura en estado sólido de algunos de estos complejos, mediante difracción de rayos-X. La utilización de los complejos catiónicos de fórmula [PdMe(NCMe)(L-L)][BAr'4] como precursores de catalizador para la reacción de copolimerización ha dado lugar a la obtención de sistemas activos, de los que pueden extraerse las siguientes conclusiones:Los complejos de paladio que contienen ligandos ditioéteres son activos como precursores de catalizador para la reacción de copolimerización de 4-tert-butilestireno con monóxido de carbono, como se explica en el Capítulo 3. Sin embargo, los complejos son poco estables en atmósfera de CO, reduciéndose a paladio metálico. Los copolímeros obtenidos con estos catalizadores presentan microestructuras muy variables dependiendo del ligando azufre-dador utilizado. Se han podido obtener copolímeros isotácticos escogiendo el ligando ditioéter con la rigidez del esqueleto y con el tamaño de quelato apropiados, concretamente con el ligando (-)-deguspri.El Capítulo 4 describe la síntesis de nuevos complejos catiónicos de Pd(II) que contienen ligandos nitrógeno-dadores derivados del pirazol. La utilización de estos ligandos planos lleva a la obtención de complejos muy activos en la reacción de copolimerización, debido a sus propiedades estéricas y electrónicas. El estudio de la actividad de los precursores catalíticos y del peso molecular de los copolímeros obtenidos, en función del tiempo de reacción ponen de manifiesto que se trata de sistemas de polimerización "living". Los polímeros obtenidos son, en todos los casos, de elevado peso molecular y sindiotácticos.La síntesis de los nuevos ligandos nitrógeno-dadores derivados de la imidazolina, que poseen variaciones estructurales sistemáticas, se presenta en el Capítulo 5. La coordinación de estos ligandos a paladio ha dado lugar a complejos neutros [PdClMe(N-N')] que presentan la misma estereoquímica independientemente del ligando utilizado. Algunos de estos complejos han sido analizados en estado sólido por difracción de rayos-X.Se han observado diferencias en las distancias de coordinación del ligando al metal, en función del substituyente que posea la imidazolina en el nitrógeno amínico. Los complejos catiónicos sintetizados presentan, en disolución, notables diferencias estereoquímicas en función de la basicidad de los ligandos nitrógeno-dador utilizados. Así pues se han obtenido selectivamente estereoisómeros en función del ligando utilizado. La actividad de estos complejos catiónicos como precursores catalíticos para la reacción de copolimerización se ha observado que depende,fundamentalmente, de la basicidad del ligando, siendo más activos los catalizadores que poseen coordinados los ligandos menos básicos. En función del precursor utilizado es posible la síntesis de copolímeros con distinto grado de estereoregularidad. Así, precursores que poseen ligandos con substituyentes en el nitrógeno amínico que retiran densidad electrónica dan lugar a copolímeros sindiotácticos. En el caso de que los ligandos posean substituyentes dadores de densidad electrónica no se ha podido establecer una relación directa entre el precursor y la tacticidad del polímero. El estudio de la reactividad de los precursores catalíticos con CO ha sido realizada "in-situ" por RMN y ha puesto de manifiesto que los complejos formados son acilos-carbonilos de paladio de fórmula [Pd(COMe)(CO)(N-N')][X].Los precursores de catalizador que contienen ligandos nitrógenodadores,derivados tanto del pirazol como de la imidazolina, han resultado ser activos en la reacción de terpolimerización de tert-butilestireno y etileno con monóxido de carbono. Las diferencias estructurales de los ligandos utilizados tienen una marcada influencia en la reactividad de los complejos de paladio con los distintos alquenos. Ésto ha llevado a la obtención de terpolímeros con diferente concentración de monómeros en función de las propiedades estructurales del ligando nitrogenado utilizado. / The development and study of new palladium catalysts for the copolymerization of 4-tert-butylstyrene with carbon monoxide was the main objective in the present thesis. The role played by the chelating ligands and in particular by their donating atoms is known to be fundamental in this catalytic process and therefore sulfur and nitrogen-donating ligands were studied. As a result from this study, the following conclusions can be drawn:The new palladium(II) neutral and cationic complexes containing bis(thio)ethers as chelating ligands, synthesized in Chapter 3, show different behavior in solution depending on the rigidity of the ligand. The cationic complexes are precursors for the copolymerization of CO/4-tertbutylstyrene although they are quite unstable under carbon monoxide pressure and get reduced to inactive palladium metal. By choosing chiral bis-(thio)ethers with the appropriate backbone rigidity, good stereocontrol of the styrene insertion in the polyketone chain may be obtained.In Chapter 4 the coordination of a family of Cs-symmetrical pyrazolcontaining bisnitrogen ligands to palladium-methyl cationic complexes leads to different stereoisomers depending on the steric hindrance of the bisnitrogen ligand. They behave as active precursors for the copolymerization reaction and allow the synthesis of syndiotactic polyketones, irrespectively of the stereochemistry of the precatalyst. Under mild copolymerization conditions the pyrazol-containing catalysts are an example of living copolymerization catalysts.Chapter 5 deals with the synthesis of new chiral N1-substituted imidazolines which allow tuning the electronic properties of the metal to which they are coordinated. The differently substituted C1-symmetrical pyridine-imidazolines may lead to the selective synthesis of palladium cationic stereoisomers depending on the basicity of the ligand. Similarly under carbon monoxide atmosphere, palladium-acyl stereoisomers may be selectively obtained. When the different stereoisomers are used as precatalysts for the copolymerization of CO and 4-tert-butylstyrene, polyketones with different degrees of stereoregularity may be obtained.The combination of a pyridine or pyrimidine ring with a 5-membered nitrogen containing heterocycle (pyrazol or imidazoline) leads to effective achiral or chiral ligands, respectively, for the CO/4-tertbutylstyrene copolymerization and also CO/ethene/4-tert-butylstyrene terpolymerization reactions, as shown in Chapter 6. The palladium precatalysts with pyrazol-containing ligands are more stable under co- and terpolymerization conditions than the imidazoline-derived ones. The steric hindrance caused by the chiral imidazoline ligands may be responsible for the low reactivity of the palladium species towards 4-tert-butylstyrene,while the insertion of ethylene is more favored. This reactivity is reversed when less steric hindered nitrogen ligands are used.

This thesis is based on experiments applying synchrotron based X-ray Absorption Spectroscopy(XAS) and Resonant Inelastic X-ray Scattering (RIXS) in the soft X-ray region to energy related systems. The main work of this thesis has been to develop a reaction cell that allowed for in situ XAS and RIXS investigations of the partial epoxidation of ethylene over a Ag catalyst at 1 atm and up to 250C. The developed in situ cell can be used in two sample modes: 1) the Ag catalyst is deposited directly onto the vacuum separating membrane with the reaction gases flowing beneath it or 2) a slightly compressed Ag powder sample is at a distance to the vacuum membrane with the reaction gases flowing between the Ag powder sample and the membrane.Both sample modes offers the total florescence yield, TFY, and the total electron yield, TEY, to be recorded simultaneously. By means of the developed in situ cell a number of oxygen species, residing in/on the Ag surface or in the Ag bulk, have been detected. We claim to detect adsorbed O2 under epoxidation conditions, as well as Ag–O–H groups. We are also able to monitor changes of the absorbed oxygen as we change the composition of the reaction gas feed. The first charging cycle of Li-ion batteries have been investigate by ex situ measurements on the cathode Li2-xMnSiO4 and the anode composite LixNi0:5TiOPO4/C . The initial crystalline material becomes amorphous due to lithiation during the first first charging. We find that the redox behaviors of these two states are significantly different. Sulfidation of natural copper oxides are is found to be strongly promoted when it is grown on the host metal by a disproportionation.

The study of organometallic chemistry in the context of catalysis can be approached from a stoichiometric perspective, in which PGM complexes are examined in the context of understanding fundamental reactions to provide insight into established catalytic transformations. Alternatively, a catalytic perspective can be adopted, in which an unknown or underdeveloped transformation is identified and PGM catalysis is employed to assist in the further development of this area. In this regard, two general goals of this thesis are: 1) to explore alternative ligation strategies based on P,S-functionalized indene ligands, with a particular focus of studying divergent stoichiometric reactivity between related cationic and zwitterionic PGM complexes; and 2) to identify general PGM catalysts for the cyclohydroamination of alkylaminoalkenes and the hydroamination of internal alkynes with secondary alkylamines. The preparation and divergent reactivity of a previously unreported class of coordinatively unsaturated cationic and zwitterionic Cp*Ir(P,S) complexes that feature structurally analogous P,S-indene and mono-deprotonated P,S-indenide ancillary ligands, respectively, are discussed. The cationic complex was observed to activate organosilanes via the first well-documented H-Si addition across an M-SR linkage. In contrast, the unusual stoichiometric reactivity of the putative zwitterion with CH3CN or Ph2SiH2 can be viewed as resulting from the dual action of the Lewis acidic Cp*Ir fragment and the Lewis basic 10?-electron indenide unit within this formally charge-separated zwitterion. Building on these initial studies, the synthesis of structurally related (benzyl)Pt(P,S) borato- and carbanion-based zwitterions and cationic complexes featuring the P,S-indene and indenide ligand framework are also presented. In the context of hydroamination studies, [Ir(COD)Cl]2 was identified as an effective pre-catalyst for the efficient synthesis of pyrrolidine and piperidine heterocycles via the cyclohydroamination of tethered aminoalkenes. Following optimization studies of this catalyst system, a broad substrate scope that included the cyclization of primary and secondary alkyl- or arylamines was established. A kinetic and mechanistic evaluation of this reaction suggested the operative pathway as involving olefin activation in a manner that had not previously been documented for Ir-catalyzed alkene hydroamination. In the pursuit of a general catalyst for the alkyne hydroamination reaction, an effective gold pre-catalyst featuring a P,N-ligand was identified and was used in the addition of a variety of functionalized dialkylamines to internal alkynes. In particular, the first examples of the regioselective addition of dialkylamines to unsymmetrically substituted alkynes are discussed. A preliminary mechanistic survey, consisting of kinetic and stoichiometric experiments, has provided empirical evidence to support a mechanism comprised of turnover-limiting alkyne insertion into a Au?N bond followed by proto-deauration.

Homogeneous organometallic species serve as useful catalysts for a vast number of chemical transformations. Ancillary ligands which bind to the metal center are employed to modulate the reactivity of the metal, and have been key to the discovery and improvement of most types of transition metal-mediated reactions. This thesis describes the design and application of P,N-ligands in platinum group-catalyzed reactions, specifically the Ru- and Ir-catalyzed ketone transfer hydrogenation (TH) and the Pd-catalyzed cross-coupling of aryl (pseudo)halides and N-H containing substrates. A zwitterionic Ru-species featuring a donor substituted P,N-indenide ligand was found to be an excellent catalyst for ketone TH, providing turnover frequencies (TOFs) as high as 300 000 h-1, while related cationic Ru-complexes ligated by P,N-indene ligands were found to be rather poor catalysts. Ir-complexes supported by either indene or indenide P,N-ligands were also found to be active TH catalysts (TOFs ~30 000 h-1), however phenylene P,N ligands, specifically (o-tBu2P-C6H4)NMe2, displayed optimal catalytic performance, allowing for rapid ketone reduction (TOFs of >100 000 h-1), at low catalyst loadings (as low as 0.004 mol% Ir). Enantioselective TH was achieved by employing the suitably substituted, commercially available P,N-ligand, Cy-Mandyphos in combination with [Ir(COD)Cl]2 and NaPF6. The use of P,N-ligands in Pd-catalyzed C-N cross coupling, specifically (o-R2P-C6H4)NMe2 (R = tBu or 1-Ad), allowed for the development of a highly versatile catalyst system for this reaction. In combination with [Pd(allyl)Cl]2 or [Pd(cinnamyl)Cl]2, the above described ligands enabled the cross-coupling of aryl and heteroaryl chlorides and bromides to a diverse range of amine and related substrates such as primary alkyl- and arylamines, cyclic and acyclic secondary amines, N-H imines, hydrazones, lithium amide, and ammonia. Reactions could be performed at low catalyst loadings (0.5-0.02 mol% Pd) with excellent functional group tolerance and chemoselectivity. The ligand N-[2-di(1-adamantylphosphino)phenyl]morpholine in combination with [Pd(cinnamyl)Cl]2 was found to provide excellent reactivity for the cross-coupling of ammonia to aryl chlorides with catalyst loadings of 0.3-5 mol% Pd. Sterically unbiased substrates containing electron-donating groups were tolerated with minimal competing diarylation. Aryl tosylates could be coupled with ammonia at room temperature and chemoselective ammonia arylation in the presence of other amine functionality was well tolerated. Pd-catalyzed cross-coupling of hydrazine with aryl chlorides and tosylates was achieved employing N-[2-di(1-adamantylphosphino)phenyl]-morpholine as the ligand. Good yields of the desired, mono-functionalized aryl hydrazine product was observed for a range of substrates at 5 mol% Pd. Selective hydrazine coupling was observed in the presence of other NH-functionality and NH-indazoles could be prepared by the tandem cross-coupling/condensation of hydrazine with 2-chlorobenzaldehydes.

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