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This thesis focuses on the properties of the diiminepyridine (DIP) ligand and its transition metal complexes, especially cobalt complexes. Existing and new X-ray structures of five-coordinate DIP Fe and Co dihalide complexes have been analyzed using the two-angle criterion ω. Substituent effects (less than 6 kcal/mol) and metal effects (mostly less than 6 kcal/mol) on structure distortion have been explored by density functional theory (DFT). The small energy barrier indicated easy distortion of the coordination geometries. The same strategy was also applied to the analysis of iron dialkyl complexes. There seems to be no direct correlation between structural preference and catalytic activity in olefin polymerization. Ligand parameters of DIP-type ligands, which intend to measure the σ-donor and π-acceptor ability, were developed using DFT calculation. The stabilization energy of the metal complexes was decomposed assuming a linear energy relationship. The results showed that the standard DIP ligand is both a strong σ-donor and a strong π-acceptor, and inferior only to the bis(carbene)pyridine ligand. A mild way to make (DIP)CoR using labile-ligand cobalt dialkyl precursors has been explored. A simple and easy way to synthesize (Py)2Co(CH2SiMe3)2 has been developed. This compound is stable at room temperature and can be further converted to (TMEDA)Co(CH2SiMe3)2 in high yield. The X-ray structure of the analogous (Py)2Co(CH2CMe2Ph)2 showed a structure similar to its iron analog. Application to DIP ligands indicates that the π-acceptor ability of the ligand determines whether cobalt(I) or cobalt(II) dialkyl will be obtained. However, steric protection is important in obtaining stable cobalt(I) alkyl complexes. Hydrogenolysis of LCoCH2SiMe3 (L: 2,6-[2,6-Me2C6H3N=C(CH3)]2C5H3N) generated LCo(N2) complex in the presence of dinitrogen. When reacted with organic halides, especially aryl chlorides, LCo(N2) broke the carbon-halogen bond through a binuclear oxidative addition mode to generate two cobalt(I) products. The radical mechanism proposed was supported by DFT studies. The resulting cobalt(I) aryl products can further react with activated alkyl halides to generate cross-coupled products, probably also through a radical mechanism. LCo(N2) can also be used to break the acyl carbon-oxygen bond of esters, although less efficiently.

This thesis focuses on the properties of the diiminepyridine (DIP) ligand and its transition metal complexes, especially cobalt complexes. Existing and new X-ray structures of five-coordinate DIP Fe and Co dihalide complexes have been analyzed using the two-angle criterion ω. Substituent effects (less than 6 kcal/mol) and metal effects (mostly less than 6 kcal/mol) on structure distortion have been explored by density functional theory (DFT). The small energy barrier indicated easy distortion of the coordination geometries. The same strategy was also applied to the analysis of iron dialkyl complexes. There seems to be no direct correlation between structural preference and catalytic activity in olefin polymerization. Ligand parameters of DIP-type ligands, which intend to measure the σ-donor and π-acceptor ability, were developed using DFT calculation. The stabilization energy of the metal complexes was decomposed assuming a linear energy relationship. The results showed that the standard DIP ligand is both a strong σ-donor and a strong π-acceptor, and inferior only to the bis(carbene)pyridine ligand. A mild way to make (DIP)CoR using labile-ligand cobalt dialkyl precursors has been explored. A simple and easy way to synthesize (Py)2Co(CH2SiMe3)2 has been developed. This compound is stable at room temperature and can be further converted to (TMEDA)Co(CH2SiMe3)2 in high yield. The X-ray structure of the analogous (Py)2Co(CH2CMe2Ph)2 showed a structure similar to its iron analog. Application to DIP ligands indicates that the π-acceptor ability of the ligand determines whether cobalt(I) or cobalt(II) dialkyl will be obtained. However, steric protection is important in obtaining stable cobalt(I) alkyl complexes. Hydrogenolysis of LCoCH2SiMe3 (L: 2,6-[2,6-Me2C6H3N=C(CH3)]2C5H3N) generated LCo(N2) complex in the presence of dinitrogen. When reacted with organic halides, especially aryl chlorides, LCo(N2) broke the carbon-halogen bond through a binuclear oxidative addition mode to generate two cobalt(I) products. The radical mechanism proposed was supported by DFT studies. The resulting cobalt(I) aryl products can further react with activated alkyl halides to generate cross-coupled products, probably also through a radical mechanism. LCo(N2) can also be used to break the acyl carbon-oxygen bond of esters, although less efficiently.

No description available.

This thesis addresses the potential for use of cobalt(III) complexes for functionalisation of lightly oxidised iron surfaces. In Chapter 2 the preparation of cobalt(III) complexes of a series of ligands based on 1,1,1-tris(aminomethyl)ethane is described. The synthesis was approached in two ways. Firstly, preparation of functionalised triol molecules as precursors to functionalised triamine ligands was investigated. This approach utilised the Tollens condensation of aldehydes with formaldehyde. In a second approach, the functionalisation of tetrakis(aminomethyl)methane in which one amine arm has been differentiated was used. The tetraamine was reacted with benzaldehyde and reduced with borohydride ion to give a secondary amine molecule that was then functionalised using alkyl or aryl sulfonyl chloride molecules. Chapter 3 describes the measurement of the binding of some cobalt(III) complexes to the surface of high surface area goethite. It was observed that complexes that have three exchangeable ligands bind more strongly than those with two exchangeable ligands. This is rationalised as being due to there being more bonds to the surface formed by complexes with three exchangeable ligands. It was also observed that complexes with three exchangeable ligands give greater surface coverage than those with two. This is likely due to the larger cross sectional area of the complexes with two exchangeable ligands in comparison to that of those with three, which blocks potential adjacent sites. Preliminary experiments on the use of the contact angle, SEM, EDS and QCM to characterise complex binding are explored in Chapter 4 . The results from the EDS and QCM experiments show that these may be valuable tools for measuring this binding and the subsequent surface properties, but have not yielded detailed results at this point. In Chapter 5 the use of cobalt(III) complexes as inhibitors of corrosion of iron in hydrochloric acid is investigated. All the complexes tested, even those that showed no binding to goethite surfaces, inhibit the corrosion to some degree. The level of inhibition is dependent on the complex, with [Co(tren)Cl2]Cl showing maximum inhibition of 81% and [Co(tame)Cl3] showing maximum inhibition of 53%. For some of the complexes, their concentration in solution over the course of the experiment was monitored by UV-vis. It was found that the complex disappears in a zero order reaction, the rate of which is dependent on the complex. However, the exact nature of this reaction is unknown. Furthermore, it was observed that inhibition of corrosion continues after the complex is no longer observed in solution. There is a difficulty in rationalising the inhibition being dependent on the complex identity, but not its continued presence in solution. Consequently, the mechanism of corrosion inhibition that explains all of these observations is still not known.

The synthesis and coordination chemistry of eleven bridging ligands, eight of which are new compounds, are described. These ligands are all based on the tridentate terpyridyl system. The other metal ion binding sites of these ligands contain pyridine/bipyridine/pyrazole rings or amine/azamacrocycles domains. In these ligands, the two metal ion binding sites are differentiated by the number of atoms in each site, the configuration of the binding site or the types of donor atom that are present. This binding site differentiation allows to use the different coordination properties of the binding sites to control the regiochemistry of the complexation, ensuring that the correct metal ion is incorporated at the correct binding site in the ligand. Many of the complexes synthesised are mono-ruthenium(II) complexes where Ru(II) ions are situated in the terpyridyl sites of the ligands. These include heteroleptic Ru(II) complexes of the type [Ru(ttp)(L)]2+, where ttp is 4'-(p-tolyl)-2,2':6',2ʺ- terpyridine, and L is the bridging ligand. Reactions of the Ru(II) complexes with a range of metal ions including Co(III) ion have been investigated. The Ru(II) complexes can be classified into three main categories depending on the type of ligands that have been employed: (1) Ru(II) complexes which can react with Co(III) ions to form heterodinuclear Ru(II)-Co(III) complexes; (2) Ru(II) complexes which react only with Ag(I) ions and no other common metal ions that we have tried; (3) Ru(II) complexes with no detectable ability to coordinate other common metal ions. Following standard cobalt chemistry, some heterodinuclear Ru(II)-Co(III) complexes of the type [(ttp)Ru(cymt)Co(X)2]3+, where X = NO2 -, Cl-, and OH-, have been successfully prepared from the corresponding Ru(II) complexes. In these heterodinuclear complexes, anions such as NO2 -, Cl-, or OH- can be readily attached to the Co(III) ions. However, attachment of a neutral species such as en ligands to the Co(III) ions in the complexes proved to be more difficult. Reactions of heterodinuclear Ru(II)-Co(III) complexes with en ligands result in removal of the cobalt ions from the complexes. This is may be a result of a significant difference in the overall charges between the complexes with anionic and the complexes with neutral ligands (3+ vs 5+). Higher overall charge of the complexes when protonable ligands such as monodentate en are present, may destabilize the complexes even more. A combination of NMR spectroscopy, ESI-MS, UV-vis spectroscopy, elemental analysis, and X-ray crystallography has been used to characterise the ligands and their complexes. The crystal structures of one new ligand and sixteen complexes are described.

L’économie actuelle repose sur l’utilisation d’énergies fossiles dont les réserves sont limitées. En plus, l’utilisation de ces ressources a un impact négatif sur l’environnement dû à l’émission des gaz polluants et du CO2. Il est donc nécessaire de remplacer les ressources fossiles par les énergies renouvelables. Les énergies renouvelables peuvent être facilement converties en électricité pour une utilisation directe, mais l’électricité ne peut pas être stockée en grande quantité. Dans ce contexte, l’hydrogène pourrait servir de vecteur énergétique. Il est possible de produire de l’hydrogène par électrolyse de l’eau. L’hydrogène sera ensuite utilisé via une pile à combustible pour fournir de l’électricité et de la chaleur. Ce procédé ne produit que de l’eau qui va être re-consommé ensuite par l’électrolyse.Ce travail de thèse est axé sur la production d’hydrogène par électrolyse de l’eau en milieu acide par la technologie PEM (proton exchange membrane). L’objectif est de remplacer le platine, catalyseur de la réduction à la cathode par des complexes de cobalt de type cobalt-oxime.Le premier chapitre traite différents aspects de l’électrolyse de l’eau et différents catalyseurs étudiés dans la littérature.Le second chapitre décrit différentes techniques expérimentales utilisées pour caractériser les complexes étudiés.Le chapitre trois décrit la synthèse et l’activité catalytique des complexes de cobalt-oxime en solution dans l’acétonitrile vis-à-vis de la réduction des protons en hydrogène.Le chapitre quatre présente les premiers travaux obtenus en utilisant les complexes de cobalt-oxime à la place du platine dans les électrolyseurs PEM. / Today's economy is base on the use of fossil fuels, whose reserves are limited. In addition, the use of these resources has a negative impact on the environment due to the emission of polluting gases and CO2. Therefore it is necessary to replace fossil fuels by renewable energy. Renewable energy can be easily converted to electricity to direct use, but electricity can not be stored in large quantities. In this context, hydrogen could be used as an energy carrier. It is possible to produce hydrogen by electrolysis of water. Hydrogen is then used via a fuel cell to supply electricity and heat. This process produces only water which will then be re-used by the electrolysis.This thesis focuses on hydrogen production by water electrolysis in acidic medium by the PEM (proton exchange membrane) technology. The goal is to replace the platinum, catalyst for proton reduction at the cathode by cobalt-oxime complexes.The first chapter describes various aspects of water electrolysis and different catalyst studied in the literature.The second chapter describes different characterization techniquesChapter three describes the synthesis and catalytic activity of the complexes of cobalt-oxime in solution in acetonitrile towards proton reduction into hydrogen.Chapter four presents the early work obtained using cobalt complexes oxime instead of platinum in PEM electrolyzers.

Submitted by Rosivalda Pereira (mrs.pereira@ufma.br) on 2017-06-02T20:09:54Z No. of bitstreams: 1 LeidianaSousaLima.pdf: 1258368 bytes, checksum: 012183297e9fc650daa7de037cb6a95b (MD5) / Made available in DSpace on 2017-06-02T20:09:54Z (GMT). No. of bitstreams: 1 LeidianaSousaLima.pdf: 1258368 bytes, checksum: 012183297e9fc650daa7de037cb6a95b (MD5) Previous issue date: 2016-09-02 / Fundação de Amparo à Pesquisa e ao Desenvolvimento Científico e Tecnológico do Maranhão (FAPEMA) / This paper presents the results obtained by quantum study applying the functional theory of density - DFT and using the B3LYP functional to verify the electronic structures of Tetraazamacrociclos Cobalt (CoN4) and their interactions with oxygen through Griffith adsorption models (Side-on) and Pauling (End-on). The initial structures of Porphyrin Cobalt complex – CoP, Octametilporfirina Cobalt - CoOMP, Tetrametilporfirina Cobalt - CoTMP, tetraaza [14] annulene Cobalt - CoTAA and Dibenzotetraaza [14] annulene Cobalt - CoDBTAA were obtained from GaussView program and optimization the geometry and charge distribution of the structures, as well as their interactions with molecular oxygen were carried out using the Gaussian 09 program. The results shows that the structure of the macrocycle ligands influence O2 binding capacity to cobalt. In evaluating the interaction with oxygen, porphyrin cobalt and its derivatives showed better evidence against group tetraaza [14] annulene, for interaction with molecular oxygen due to weakening of the bond in the O2 molecule characteristic enhanced by data from Mulliken charge. Therefore, the order of interaction presented by the studied complexes is CoTMP, CoOMP, CoP, CoDBTAA and CoTAA in End-on model and CoP CoOMP, CoTMP, CoDBTAA and CoTAA in side-on model. / Este trabalho apresenta os resultados obtidos por meio estudo quântico aplicando a Teoria do Funcional da Densidade – DFT e usando o funcional B3LYP para verificar as estruturas eletrônicas de Tetraazamacrociclos de Cobalto (CoN4) e suas interações com o oxigênio por meio dos modelos de adsorção de Griffith (Side-on) e Pauling (End-on). As estruturas iniciais dos complexos Porfirina de Cobalto - CoP, Octametilporfirina de Cobalto - CoOMP, Tetrametilporfirina de Cobalto - CoTMP, Tetraaza[14]anuleno de Cobalto - CoTAA e Dibenzotetraaza[14]anuleno de Cobalto - CoDBTAA foram obtidas do programa GaussView e a otimização das geometrias e a distribuição de carga das estruturas, bem como as suas interações com o oxigênio molecular, foram realizadas com o uso do programa Gaussian 09. Os resultados obtidos comprovam que a estrutura dos ligantes do macrociclo influência a capacidade de ligação do O2 ao cobalto. Na avaliação da interação com oxigênio, a Porfirina de Cobalto e seus derivados mostraram uma melhor evidência, frente ao grupo Tetraaza[14]anuleno, para a interação com o oxigênio molecular devido ao enfraquecimento da ligação na molécula de O2, característica reforçada pelos dados provenientes da carga Mulliken. Portanto, a ordem de interação apresentada pelos complexos estudados é CoTMP, CoOMP, CoP, CoDBTAA e CoTTA no modelo End-on e CoP, CoOMP, CoTMP, CoDBTAA e CoTAA no modelo side-on.

The synthesis and coordination chemistry of eleven bridging ligands, eight of which are new compounds, are described. These ligands are all based on the tridentate terpyridyl system. The other metal ion binding sites of these ligands contain pyridine/bipyridine/pyrazole rings or amine/azamacrocycles domains. In these ligands, the two metal ion binding sites are differentiated by the number of atoms in each site, the configuration of the binding site or the types of donor atom that are present. This binding site differentiation allows to use the different coordination properties of the binding sites to control the regiochemistry of the complexation, ensuring that the correct metal ion is incorporated at the correct binding site in the ligand. Many of the complexes synthesised are mono-ruthenium(II) complexes where Ru(II) ions are situated in the terpyridyl sites of the ligands. These include heteroleptic Ru(II) complexes of the type [Ru(ttp)(L)]2+, where ttp is 4'-(p-tolyl)-2,2':6',2ʺ- terpyridine, and L is the bridging ligand. Reactions of the Ru(II) complexes with a range of metal ions including Co(III) ion have been investigated. The Ru(II) complexes can be classified into three main categories depending on the type of ligands that have been employed: (1) Ru(II) complexes which can react with Co(III) ions to form heterodinuclear Ru(II)-Co(III) complexes; (2) Ru(II) complexes which react only with Ag(I) ions and no other common metal ions that we have tried; (3) Ru(II) complexes with no detectable ability to coordinate other common metal ions. Following standard cobalt chemistry, some heterodinuclear Ru(II)-Co(III) complexes of the type [(ttp)Ru(cymt)Co(X)2]3+, where X = NO2 -, Cl-, and OH-, have been successfully prepared from the corresponding Ru(II) complexes. In these heterodinuclear complexes, anions such as NO2 -, Cl-, or OH- can be readily attached to the Co(III) ions. However, attachment of a neutral species such as en ligands to the Co(III) ions in the complexes proved to be more difficult. Reactions of heterodinuclear Ru(II)-Co(III) complexes with en ligands result in removal of the cobalt ions from the complexes. This is may be a result of a significant difference in the overall charges between the complexes with anionic and the complexes with neutral ligands (3+ vs 5+). Higher overall charge of the complexes when protonable ligands such as monodentate en are present, may destabilize the complexes even more. A combination of NMR spectroscopy, ESI-MS, UV-vis spectroscopy, elemental analysis, and X-ray crystallography has been used to characterise the ligands and their complexes. The crystal structures of one new ligand and sixteen complexes are described.