Gold was considered for a long time to be an inert metal and was only in 1986 that the first homogeneous gold-catalyzed transformation was reported. In our laboratory, we isolated a surprisingly stable vinyl complex that resulted from an unexpected 1,2-silyl migration while working on a gold(I)-catalyzed reaction for the synthesis of polyprenylated polycyclic acylphloroglucinols (PPAPs). We herein report the isolation of a variety of organogold species where we could control the silyl migration based on the nature of the silyl group installed on the terminal alkyne. Silyl groups bearing an aromatic ring inhibited the silyl migration while the aliphatic silyl group afforded the 1,2-silyl migrated adduct. After mechanistic investigation of this intriguing migration, we believe that this process goes through a relatively rare gold vinylidene intermediate. More than 15 organogold complexes were isolated in good yield and characterized by x-ray crystallography. Investigation of their reactivity led to the formation of C(sp3)-C(sp2) bonds using electrophilic reagents without the use of Pd-based catalysts. We have also developed a new gold(I)-catalyzed dehydro Diels-Alder reaction using a simple monocyclic silyl enol ether. This methodology proceeds effectively with a wide scope by the use of [JackiephosAu(NCMe)]SbF6 in toluene. This methodology was then applied to the synthesis of magellanine, an architecturally complexed angular natural product isolated in 1976 from the club moss Lycopodium Magellanicum. The key step precursor was rapidly constructed via a Mitsunobu/Diels-Alder reaction that generated the requisite carboxaldehyde. The dehydro Diels-Alder reaction afforded the molecular skeleton of magellanine diastereoselectively in 91% yield. The synthesis was successfully accomplished in 11 steps demonstrating the ability of the gold(I) salt to rapidly construct complex molecules. Since the discovery of salvinorin A, a lot of efforts were exerted in order to optimize the biological activity for treatment of central nervous system disorders. Development of a new synthetic routes to salvinorins are essential to afford novel functionalized analogues. The decalin framework of salvinorin A was assembled with a Diels-Alder reaction with Et2AlCl followed by a gold(I)-catalyzed 6-endo-dig carbocyclization with [JohnphosAu(NCMe)]SbF6. Further functionalization afforded an elaborated intermediate which possesses the correct stereochemistry of the natural product. Following these promising results, efforts are currently in progress for the completion of the total synthesis.

Chapter 1 describes an introduction to the area of organocatalysis and delineates previous work within the Smith group on the use of isothioureas in asymmetric catalysis. Chapter 2 showcases a one-pot isothiourea-catalysed Michael addition-lactamisation using cheap and readily available starting materials (carboxylic acids) and easily prepared α,β-unsaturated ketimines via an ammonium enolate intermediate to give dihydropyridinones with high diastereo- and enantioselectivity (typically >90:10 dr, up to 99% ee). The resultant dihydropyridinones can be successfully derivatised into multiple products without erosion of stereointegrity. In chapter 3 the same concept has also been applied to the synthesis of planar molecules by using (phenylthio)acetic acid as a suiTable ammonium enolate precursor. Generation of an ammonium enolate using an achiral isothiourea (DHPB) and reaction with α,β-unsaturated trifluoromethyl ketones allows an isothiourea-mediated Michael addition / lactonisation / thiophenol elimination cascade reaction for the formation of 4,6-disubstituted and 3,4,6-trisubstituted 2-pyrones in good to excellent yields (61-99%). Notably this method allows low catalyst loadings of 1% to be used. The methodology has successfully been applied to the synthesis of a COX-2 inhibitor and a wide range of derivatisations has been performed, giving valuable aromatic and heteroaromatic products containing the trifluoromethyl motif. In chapter 4 a novel N- to C-sulfonyl migration of dihydropyridinones via photoisomerisation is investigated. The scope and limitations of this process is investigated and the process is shown to proceed without compromising the diastereo- or enantiomeric purity of the starting material, giving 5-sulfonyl products in good to excellent yields (67-95%). Mechanistic crossover has indicated that this migration includes an intermolecular step, while EPR studies provided evidence of its radical nature.

Promoter effects on SBA-15 supported iron Fischer-Tropsch catalysts were investigated for their potential to improve high temperature catalyst performance. FTS catalysts promoted by manganese (0.15%-1.4%), copper (0.15%-1%), and potassium (0.5%-3%), with all percentages stated on the basis of mass percentage of final catalysts, were prepared and tested at 430°C and ambient pressure in a fixed bed reactor. Manganese showed the ability to promote the FT reaction, increasing both the CO conversion and the average chain length of hydrocarbon products. Compared to the unpromoted catalyst composed only of iron supported on SBA-15, 1.4%Mn (mass) promotion of 15% (mass) iron on SBA-15 improved CO conversion from 29% to 32%, increased alpha from 0.21 to 0.34, decreased carbon dioxide selectivity from 76% to 50%, increased C2-C4 selectivity from 9.6% to 30% and increased C5+ selectivity from 0.21% to 2.2%. Copper promotion gave increased conversion, but did not significantly affect alpha or carbon dioxide selectivity. Potassium promotion in the range of 0.5% to 3% by mass, on the other hand, had a negative effect on CO conversion at all concentrations tested.

The use of rare and expensive noble metals in the chemical industry as organometallic catalysts has grown exponentially in the past few decades due to their high activity, selectivity and their ability to catalyze a wide range of reactions. With this growth in use has also come a proportional growth in concern as these toxic metals inevitably leach into the environment and their negative effects on public health and our ecosystems are becoming better understood. First-row transition metal catalysts provide both environmental and economic benefits as alternatives to these noble metals due to their lower toxicity and cheaper costs. The two-electron chemistry that makes the noble metals so attractive however, is more challenging to accomplish with first-row transition metals. Intelligently designing the ligand scaffold which surrounds the metal can mitigate or even eliminate some of the shortfalls of these first-row metals. Some key features that should be considered when designing a ligand are: 1) a strong chelating ability so the ligand can stay attached to the metal, 2) incorporation of strong donors to favour low-spin complexes, 3) inclusion of hemilabile groups to allow for substrate activation and metal stabilization throughout various oxidation states, 4) redox activity to be able to donate or accept electrons, and 5) inclusion of Lewis base functionalities which are able to assist the substrate activation. Ligands which incorporate these features are known as bifunctional ligands as they can accomplish more than one function in the catalytic cycle. Developing first-row transition metal complexes containing these ligands may enable these species to replicate the reactivity and selectivity generally associated with the precious metals. Being able to replace the noble metals used in industry with these catalysts would have tremendous environmental and economic benefits. The objective of this thesis is to advance the field of bifunctional catalysis by examining the behaviour of two sterically svelte, tridentate SNS ligands containing hard nitrogen and soft sulphur donors when bonded to cobalt. Previous work with iron provides a template of the ligand behaviour to which cobalt can be compared, allowing us to contrast the effects exerted by the different metals. After an introduction to bifunctional catalysis in Chapter 1, Chapter 2 describes the reactivity of the amido ligand, SMeNHSMe, with precursors ranging from Co(I) to Co(III), all of which yielded the 19e- pseudooctahedral cobalt(II) bis-amido complex, Co(SMeN-SMe)2 characterized by 1H NMR spectroscopy, single-crystal X-ray crystallography and cyclic voltammetry. Although this complex has a similar structure as the Fe analogue, the cobalt bis-amido complex did not exhibit the same hemilabile behaviour that allowed for simple ligand substitution of one of the thioether groups. Instead it reacted reversibly with 2,2’-bipyridine while 1,2-bis(dimethylphosphino)ethane (DMPE) and 2,6-dimethylphenyl isocyanide both triggered additional redox chemistry accompanied by the loss of protonated SMeNHSMe. In contrast, protonation gave the cobalt(II) amido-amine cation, [Co(SMeNSMe)(SMeNHSMe)](NTf2), which allowed for substitution of the protonated ligand by acetonitrile, triphenylphosphine and 2,2’-bipyridine based on 1H NMR evidence. The ability of Co(SMeNSMe)2 to act as a precatalyst for ammonia-borane dehydrogenation was also probed, revealing that it was unstable under these conditions. Addition of one equivalent of DMPE per cobalt, however, resulted in better activity with a preference for linear aminoborane oligomers using ammonia-borane and, surprisingly, to a change in selectivity to prefer cyclic products when moving to methylamine-borane. Chapter 3 delves into the chemistry of the thiolate ligand, SMeNHS, which formed a new 18e- cobalt(III) pseudooctahedral complex, Co(S-NC-)(SMe)(DEPE), from oxidative addition of the Caryl-SMe bond. Scaling up this reaction resulted instead in formation of an imine-coupled [Co(N2S2)]- anion which was characterized by 1H NMR/EPR spectroscopy, single-crystal X-ray diffraction, cyclic voltammetry and DFT studies. The latter revealed an interesting electronic structure with two electrons delocalized in the ligand, demonstrating the non-innocent nature of the N2S2 ligand. While the analogous iron complex proved to be an effective pre-catalyst for the hydroboration of aldehydes with selectivity against ketones, this behaviour was not observed with [Co(N2S2)]- which gave a slower rate and less selectivity. The knowledge acquired from this thesis work has advanced the field of bifunctional catalysis by extending the application of these two SNS ligands from iron to cobalt, revealing unpredictable differences in reactivity between the metals. By comparing the behaviour of these ligands with iron and cobalt, we gain a better understanding of the chemistry that is accessible by these ligands and the applications for which they may be used. This increased knowledge contributes to our long-term goal of replacing expensive and toxic noble metals with more benign first-row transition metals, improving the sustainability of the chemical industry.

Made available in DSpace on 2014-10-09T12:40:52Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:07:28Z (GMT). No. of bitstreams: 1 02950.pdf: 4952382 bytes, checksum: 1dddfe6ca71077632e2bdf2d56006ba7 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / As pilhas a combustível são uma alternativa para gerar energia sem poluir o meio ambiente. Elas produzem energia elétrica pela reação do hidrogênio com o oxigênio do ar. O produto da reação é a água. É uma forma de geração de energia bastante interessante por ser uma tecnologia limpa. O hidrogênio utilizado como combustível para as pilhas a combustível, proveniente da reforma a vapor de hidrocarbonetos, contém cerca de 1% de monóxido de carbono. O hidrogênio, usado como combustível para pilha a combustível de membrana polimérica eletrolítica (PEMFC), não pode conter mais de 10 ppm de monóxido de carbono. A presença de monóxido de carbono em concentrações acima de 10 ppm envenena o anodo de Pt da célula. Neste trabalho foram estudados catalisadores que podem ser usados para oxidar monóxido de carbono seletivamente na presença de hidrogênio. Os catalisadores estudados para a oxidação seletiva de CO foram: 1%Pt/Al2O3, 1%Pt-1%Cu/Al2O3, 1%Pt/Nb2O5, 1%Pt-1%Cu/Nb2O5, 1%Cu/Al2O3, 1%Cu/Nb2O5, Al2O3 e Nb2O5. Os catalisadores suportados em Nb2O5 apresentaram melhor seletividade em relação aos catalisadores suportados em Al2O3 devido ao efeito de interação metal-suporte (SMSI) dos catalisadores suportados em Nb2O5 que diminuiu a adsorção dissociativa do H2. A adição do Cu promoveu a reação de oxidação do CO, aumentando a seletividade para a formação do CO2 devido à interação da Pt com o Cu. Os catalisadores à base de Pt testados apresentaram 100% de conversão de CO a CO2 em torno de 100C. Melhores resultados foram obtidos quando os catalisadores foram reduzidos a 300C, a seletividade dos catalisadores foi menor quando reduzidos a 500C. A seletividade foi de 47% para o catalisador Pt/Al2O3, 58% para o catalisador PtCu/Al2O3 e de 54% para o catalisador Pt/Nb2O5. O catalisador PtCu/Nb2O5 reduzido a 300C apresentou a melhor seletividade entre os catalisadores testados, em torno de 64%, tanto pela interação bimetálica da platina com o cobre quanto pela interação da fase ativa com o suporte. Os óxidos Al2O3 e Nb2O5 apresentaram 100% de conversão de CO embora a temperatura de ignição tenha sido maior em relação aos catalisadores à base de Pt, a Al2O3 apresentou 25% de seletividade enquanto que a Nb2O5 apresentou 49% de seletividade. O catalisador Cu/Al2O3 não apresentou atividade para a oxidação seletiva de CO. Já o catalisador Cu/Nb2O5, quando ativado a 300C, apresentou 100% de conversão de CO em torno de 230C com 40% de seletividade. / The fuel cells are an alternative to generate energy without polluting the environment. They produce electric energy through the reaction of hydrogen with the oxygen from air. The product of the reaction is water. It is an interesting form of generation energy because its a clean technology. The hydrogen used as combustible for the fuel cells is proceeding from the steam reform hydrocarbons, this hydrogen contains about 1% of carbon monoxide. The hydrogen, used as combustible for the polymer electrolytic membrane fuel cell (PEMFC), can not contain more than 10 ppm of carbon monoxide. The presence of carbon monoxide in concentrations above 10 ppm poisons the anode of Pt of the cell. In this work it was studied catalyst that can be used to oxidize carbon monoxide selectively in the presence of hydrogen. The catalysts studied for the selective oxidation of CO had been: 1%Pt/Al2O3, 1%Pt-1%Cu/Al2O3, 1%Pt/Nb2O5, 1%Pt-1%Cu/Nb2O5, 1%Cu/Al2O3, 1%Cu/Nb2O5, Al2O3 and Nb2O5. The catalysts supported on Nb2O5 had better selectivity in relation to the catalysts supported in Al2O3 due to the strong metal-support interaction effect (SMSI) that occurs in the catalysts supported in Nb2O5. The addition of the Cu promoted the reaction, increasing the selectivity for the oxidation of the CO due to the interaction of the Pt with the Cu. The Pt based catalysts had 100% of CO conversion to CO2 around 100C. Better results had been gotten when the catalysts were reduced at 300C, the selectivity of the catalysts was lesser when reduced at 500C. The selectivity was 47% for the Pt/Al2O3 catalyst, 58% for the PtCu/Al2O3 catalyst and 54% for the Pt/Nb2O5 catalyst. The PtCu/Nb2O5 catalyst reduced at 300C presented the best selectivity among the tested catalysts, around 64%, as much for the bimetallic interaction of platinum with copper how much for the interaction of the active phase with the support. The oxides Al2O3 and Nb2O5 had presented 100% of CO conversion even though the ignition temperature had been lesser in relation to the Pt based catalysts, the Al2O3 presented 25% of selectivity while that the Nb2O5 presented 49% of selectivity. The Cu/Al2O3 catalyst did not present activity for the selective oxidation of CO already the Cu/Nb2O5 catalyst, when activated 300C, it presented 100% of CO conversion around 230C with 40% of selectivity.

No description available.

As part of a worldwide effort to develop efficient catalysts for use in organic chemistry and in the synthesis of highly valuable molecules, work performed during the course of my stay in St Andrews has focused on the design and synthesis of new group 11 metal complexes for their applications in catalysis. The aim of this work was to develop new, active and stable, easy to synthesise group 11 complexes and investigate their catalytic activity as well as to try to understand their mode of action. Two different types of complexes were explored in order to develop more active catalysts: the neutral N-Heterocyclic carbene metal complexes and the cationic derivatives. More than 20 new catalysts were developed and their reactivity studied in different catalytic reactions. New hydroxide and tert-butoxide copper(I) or silver(I) complexes were developed and compared to the common NHC metal systems. Overall, the neutral NHC-metal catalysts showed to be highly active in a broad range of applications: in the methylation of amines using CO₂ as a C1 source, in a multicomponent reaction (A³ coupling) and in dual catalysis (hydrophenoxylation). Additionally, mechanistic studies were undertaken to obtain a greater understanding of these transformations and to possibly lead to the design of new generations of catalyst. Regarding the cationic NHC metal complexes, a straightforward methodology was developed leading to a library of highly stable catalysts. Bis-NHC, mixed NHC/ phosphine as well as NHC/pyridine species were efficiently synthesised using thermal or microwave heating, in high purity and yields. In addition, the effect of the presence of two different or identical ligands on catalytic reactivity was investigated in the 3+2 cycloaddition and in the alkynylation of ketones. Insight into the catalytic cycle was obtained via mechanistic studies. These showcased the release of one ligand during the catalytic cycle and the crucial role of this ligand displacement in generating the catalytically relevant active species. The results highlight the importance of understanding the reactivity of catalyst in order to develop new and improved ones.

Made available in DSpace on 2014-10-09T12:40:52Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:07:28Z (GMT). No. of bitstreams: 1 02950.pdf: 4952382 bytes, checksum: 1dddfe6ca71077632e2bdf2d56006ba7 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

M.Sc. (Chemistry) / Please refer to full text to view abstract