Ce travail consiste en l'étude théorique DFT des mécanismes de couplage. Le couplage déshydrogénant de stannanes implique la formation in situ d'un stannylène, formation possible grâce à l'inertie de la paire libre et au caractère acide de Lewis des stannylènes. Le couplage entre un carboxylate aromatique et un arène Ar-H commence par la décarboxylation en 2 étapes (isomérisation et désinsertion de CO2) sur un complexe de Pd(II) et se poursuit par une étape de CMD. Celle-ci est facilitée par la présence de fluors en ortho sur Ar-H essentiellement en raison du renforcement de la liaison M-C qu'ils induisent. Le couplage entre un arène et un alcyne catalysé par Ni(0)L présente une étape originale de transfert d'hydrogène de l'arène sur l'alcyne concerté avec la création de deux liaisons M-C (M-aryl et M-vinyl). Cette étape est à nouveau associée à une barrière d'activation plus basse en présence de fluors sur l'arène. L'hydroboration avec ouverture de cycle d'alkylidenecyclopropane en présence de Rh(I) nécessite la création de deux sites vacants pour que l'étape souhaitée d'ouverture de cycle soit favorisée par rapport à une étape d'élimination réductrice C-B. / This work is a theoretical study with DFT method of coupling reactions. The dehydrogenating coupling of stannanes proceeds via the formation of stannylene. This is made possible because of the chemical inertness of the lone pair and the Lewis acid character of stannylene. Coupling an aromatic carboxylate and an arene Ar-H on a Pd(II) complex is initiated by a 2-step reaction (isomerization and decarboxylation). The CMD reaction that follows is facilitated by ortho fluorine subtituents on the arene ArH because of the strengthening of the resulting Pd-C bond. The coupling between an arene and an alkyne by a Ni(0)L catalyst starts by an unusual hydrogen transfer from the arene to the alkyne, concerted with the formation of two NiC (aryl and vinyl) bonds. The energy barrier of this elementary step is lowered by fluorine subtituents on the arene. The hydroboration with ring opening of alkylidenecyclopropane in presence of Rh(I) complex is feasible only with two empty coordination sites during the key ring-opening step. Under these conditions, the ring opening is favored over the reductive elimination C-B.

L’utilisation massive de ressources fossiles carbonées pour des applications énergétiques est aujourd’hui pointée du doigt comme responsable du changement climatique. Le CO₂ émis lors de la combustion de ces ressources augmente l’effet de serre, induisant ainsi un réchauffement de la planète. Afin d’atténuer ce changement climatique, l’utilisation des énergies renouvelables est de plus en plus favorisée et le stockage de cette énergie sous forme d’hydrogène semble prometteur pour pallier à l’intermittence saisonnière de ces ressources. Une voie de stockage de l’hydrogène consiste à le faire réagir avec du CO₂ afin d’obtenir des carburants liquides telles que l’acide formique et le méthanol. Ces liquides peuvent alors être transportés facilement et lorsque l’énergie vient à manquer l’hydrogène peut être régénéré par déshydrogénation de ces molécules grâce à des catalyseurs. Dans cette thèse nous avons développé des complexes organométalliques en vue d’activer CO₂ et H₂, ce qui nous a permis d’acquérir un savoir fondamental. Le ligand triphos étant très connu pour coordiner des complexes qui catalysent ces réactions d’hydrogénation et de déshydrogénation, nous nous sommes d’abord concentrés sur le développement de ligands similaires. Nous avons synthétisé de nouveaux complexes de Fe (II), Co (II) et Cu (I) avec ces ligands. Ceux-ci se sont révélés actifs en hydroboration du CO₂. Un complexe de ruthénium a été greffé sur silice par son ligand, afin de pouvoir être recyclé lors des catalyses. Dans une deuxième partie, nous avons synthétisé un nouveau ligand aux des propriétés participatives potentielles. Un complexe de cuivre(I) coordiné par ce ligand a permis d’activer H₂ grâce à une participation métal-ligand.Enfin, un complexe de cobalt(I) coordiné par ce ligand est le premier composé à base de cobalt capable de déshydrogéner l’acide formique. / The extensive use of fossile fuel is currently causing climate change. Anthropogenic emissions of CO₂ enhance the greenhouse effect, resulting in global warming. In order to mitigate this climate change, the share of renewable energy is increasing and hydrogen seems to be a good candidate to stock energy to compensate the seasonal variations of those energies. One way to store H₂ is the hydrogenation of CO₂ to synthesise liquid molecules as formic acid and methanol. Those liquids can be conveyed in an easier way. In case of a lack of energy, H₂ can be recovered through dehydrogenation of those molecules thinks to catalysts. In this thesis, we studied the synthesis of organometallic complexes able to activate those small molecules, thus, growing a fundamental knowledge. As a number of triphos-metal complexes are known to catalyse hydrogenation and dehydrogenation reactions, we focused on the elaboration of ligands alike. With those ligands in hand, several non-noble metal based complexes (Fe (II), Co (II) and Cu (I)) were synthesized, which are active in CO₂ hydroboration catalysis. A complex of ruthenium(II)was grafted on silica through one of this ligand, in order to recycle it when it used as a catalyst. On the second hand, we designed a new ligand which could favor metal-ligand cooperativity. H₂ was succesfully activated with a copper(I) complex coordinated by this ligand, demonstrating that cooperation of the ligand. Finally, the first known cobalt complex active in dehydrogenation of formic acid was synthesised.

This thesis deals with single-electron transfer (SET) radical processes mediated by ferrocenium hexafluorophosphate and TEMPO and their application in the total synthesis of natural products. Asymmetric aminooxygenation methodology for the synthesis of anti-β-amino-α-hydroxy acid derivatives has been developed by utilizing a highly diastereoselective aza-Michael addition of chiral lithium amides to various α,β-unsaturated esters or amides/SET oxidation/radical α-oxygenation. The potential of this methodology was demonstrated in short total syntheses of the anti-β-amino-α-hydroxy acid fragments of the macrocyclic (depsi)peptides perthamide C and largamide H, and (-)-cytoxazone, which is a selective modulator of TH2 cytokine secretion. The SET-catalyzed asymmetric tandem lithium amide conjugate addition/5-exo radical cyclization/oxygenation reactions were applied in the synthesis of highly substituted pyrrolidines, azabicyclo[n.3.0]alkanes and spiropyrrolidines. An enantioselective total synthesis of the pyrrolidine alkaloid (-)-α-kainic acid was accomplished by employing the SET-catalyzed 5-exo radical cyclization/oxygenation.

<p> Ring opening of heterocyclic compounds through C-X bond cleavage is a useful strategy that provides rapid access to highly functionalized acyclic building blocks. In recent years, much work has focused on using transition metal catalysts to activate the C-X bonds of heterocycles and initiate ring opening. Metal-catalyzed ring opening of unstrained heterocycles is less prevalent than catalytic activation of strained heterocycles, which is advantageously driven by relief of ring strain. Methods for catalytic ring activation of unstrained heterocycles exist but are limited. Herein, we report the use of chiral cobalt complexes as catalysts for enantioselective ring opening of dihydrofuran and nitrogen-protected pyrrolines by utilizing dichloroalkenes as vinylidene precursors, Zn as a reductant, and ZnCl2 as an additive. Based on preliminary mechanistic studies, we believe this method proceeds through [2 + 2] cycloaddition between the ligated cobalt vinylidene species and the heterocycle, followed by β-heteroatom elimination, cobalt to zinc transmellation, and protonation to give rise to synthetically useful chiral allylic alcohol and amine products. </p>

<p>  </p> <p>Actinide complexes have been targeted for their potential in group transfer applications. The study of these metals, such as thorium and uranium, is essential to better understand the reactions these metals are capable of facilitating.  Hydrotris(pyrazolyl)borates such as hydrotris(3,5-dimethylpyrazolyl)-borate (Tp*) and hydrotris(pyrazolyl)-borate (Tp) are superbulky, scorpionate ligands that have previously been used to synthesize novel uranium complexes and probe the reactivity of these materials. Similar thorium analogs have also been synthesized, but their reactivity has yet to be explored in great depth. Tp*ThCl3(THF) and Tp2ThCl2 have been reproduced and investigated as possible starting materials for such reactivity studies. While the former was found to be largely unreactive, the latter presents promising reactivity for the synthesis of thorium-element multiple bonds, and a novel thorium imido, Tp2Th(NDipp)(THF), has been synthesized and characterized using this scaffold. </p> <p><br></p> <p>The reactivity of a uranium tetrakis(imido), [U(NDipp)4][K2], has also been investigated to probe the prospect of group transfer reactions for potential catalysis applications in the future. An isocyanate, PhNCO, was reacted with this compound; the observed product showed that group transfer was incomplete, and a four-membered metallocycle product is likely formed instead. The synthesis of a novel thorium tris(imido) has also been targeted, and preliminary results are outlined. </p>

<p>Solid-state (SS) luminescent materials are an important class of materials in a myriad of technological applications including light-emitting devices (LEDs) and displays, SS lasers, sensors, imaging agents, etc. Unfortunately, the design of efficient SS emitters is often plagued by sensitivity to environment/matrix (e.g. aggregation-induced quenching, AIQ), competing non-radiative relaxation pathways, and complicated emission mechanisms that are difficult to systematically study and tune. Copper-based systems have been proven to be good candidates for SS emissive materials due to their low-cost, high synthetic variation and well-defined features. Examples of copper-cluster systems, specifically, have been shown to be highly stable, exhibit high photoluminescent quantum yields (ΦPL), and are often relatively insensitive to environmental changes. However, many of these systems are complicated in nature, and often evoke additional relaxation pathways. To mitigate these issues, tetranuclear Cu(I)-pyrazolate complexes have been made which exhibit high ΦPL, matrix insensitivity and proceed through one major radiative emission pathway: cluster-centered based phosphorescence (3CC). The pyrazoles are highly tunable, and by increasing the size of the ligand substituents (H, F, Cl/Me/Br), a rigidochromic effect is observed, causing a significant blue-shift in their photoluminescence, making these viable materials for organic LEDs (OLEDs), especially in the deep-blue region. Furthermore, by increasing the chain length of the ligand substituent (e.g., Me → Et), another material which exhibits stimuli-responsive luminochromism in response to solvent vapor or heat can be achieved. This material exhibits blue ↔ green rigidochromic luminescence in response to stimuli via isomerization of the ethyl units from exo ↔ endo resulting in additional steric effects that effectively prevent rigidification of the Cu4 cluster. This additional phenomenon opens the door for further exploration of Cu(I)-pyrazolate complexes for stimuli-responsive luminescent materials (SRLMs) applications.</p>

<p dir="ltr">Vinylidenes are highly reactive intermediates that undergo a variety of chemical reactions. Our group has pioneered the in-situ generation of vinylidenes from bench stable 1,1-dichloroalkenes using transition metal catalysts and an exogenous reductant.</p><p dir="ltr">Herein, we demonstrate the intramolecular insertion of vinylidenes into Si–H bonds for the synthesis of unsaturated silacycles of different ring sizes. It is well known that the replacement of carbon for silicon are of significant interest to medicinal chemists as a strategy for improving the potency or pharmacokinetic properties of biologically active compounds. This method provides convenient access to trisubstituted vinyl silanes which are synthesized intermolecularly, including those that can be used as nucleophilic partners in Hiyama cross-coupling reactions. Finally, deuterium isotope labelling experiments reveal interesting mechanistic features of the reaction.</p><p dir="ltr">The second chapter of the thesis further highlights the reactivity of vinylidenes through utilizing a cobalt catalyst. Vinylidene complexes can be added into an alkyne intramolecularly followed by a cobalt to zinc transmetalation step. The resulting organozinc intermediate can be trapped with various electrophiles. Further, by altering the reaction condition, the cobaltacycle intermediate can be accessed using π systems to form different cycloadducts.</p>

No description available.

Ph. D. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / A major challenge for this generation is cleaning up heavy metal pollution disposed during industrial, domestic and agricultural activities. So, to obtain clean water resources, new treatment technologies are needed that can be applied to a broad range of highly toxic heavy metals in water. In this study, metal organic frameworks (MOFs) were synthesized from 1,2,4,5-tertabenzene carboxylic acid with metal salts of; cobalt, copper, iron, antimony, strontium and lanthanum through solvothermal method. The synthesized MOFs were reacted with polyvinyl alcohol (PVA) by electrospinning. To the best of our knowledge it is for the first time that such hybrid materials are synthesized and reported. PVA/MOF materials were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetry analyzer (TGA). The SEM micrographs of PVA/MOFs materials showed relatively uniform nanofibers that were non-beaded and entangled. Some formed patches, while others were partially cross linked. TGA analysis revealed that PVA/MOF nanofibers exhibited higher decomposition temperature than PVA nanofibres. Thus, it confirmed the interactive force between MOF and PVA nanofibres. FTIR plots also exhibited shifts in critical functional group positions, thus it confirmed that there was a given amount of MOFs embedded in the electrospun fibrous mat. PVA/MOFs materials were used in the adsorption of lead ions in solution to study the effects of temperature, time dependant studies and concentrations. The batch adsorption experiments were performed at five different Pb(II) ion concentrations (20, 40, 60, 80 and 100 mg/L), four different temperatures (25, 40, 60 and 80 oC), time dependent studies ranged from (5, 10, 30 and 60 min) and pH of all Pb(II) solutions were recorded to be 5.05. The results indicated that the uptake performance of PVA and PVA/MOFs nanofibers significantly changed with concentration, temperature and time. The PVA/MOFs nanofiber hybrids demonstrated greater adsorption percentage and adsorption capacity for Pb(II) ions than PVA nanofibers. PVA nanofibers showed moderate adsorption percentage and capacity performance of 25.5 % and 44.13 mg/g (meaning 44.13 mg of Pb(II) per gram of PVA nanofibers) while PVA/MOFs nanofibers showed improved percentage and capacity perfomance (PVA/Cu-MOFs 76.36 % and 152.72 mg/g), (PVA/Co-MOFs 59.41 % and 99.28 mg/g), (PVA/La-MOFs 92.27 % and 184.03 mg/g), (PVA/Cd-MOFs 83.19 % and 165.94 mg/g), (PVA/Sb-MOFs 50.66 % - 91.57 mg/g), (PVA/Sr-MOFs 58.85 % - 124.82 mg/g) and (PVA/Fe-MOFs 56.76 % - 108.82 mg/g). The adsorption data of Pb(II) ions on PVA and all PVA/MOFs nanofibers showed that a pseudo-second order kinetic model was more suitable than a pseudo first order kinetic model. The adsorption rate was much faster on PVA/MOFs nanofibers. This is marked by lower activation energy compared to PVA nanofibers activation energy. The Temkin model did not correlate well with all the adsorption data. On the contrary, Freundlich and Langmuir isotherm models described the adsorption data adequately. All PVA/MOFs nanofibers followed Langmuir isotherm model, only PVA nanofibers followed Freundlich isotherm model. The PVA and PVA/MOFs nanofibers gave negative values of enthalpy change (ΔHo) and negative values of Gibbs free energy change (ΔGo) showing the adsorption processes were exothermic and spontaneous. Moreover, obtained positive entropy changes (ΔSo) on PVA, PVA/Fe-MOF, PVA/Cu-MOF, PVA/Co-MOF and PVA/Sb-MOF nanofibers showed that the sorped Pb(II) ions were not restricted on the electrospun nanofibres and physisorption mechanism was dominant, while negative entropy changes (ΔSo) on PVA/Sr-MOF and PVA/La-MOF nanofibers indicated that chemisorption was more dominant. The influence of ubiquitous cations such as Ca(II) and Mg(II) on the adsorption of Pb(II) ions onto PVA and PVA/MOF nanofibers was also assessed. The results showed that the ubiquitous ions had no significant influence on the sorption of Pb(II) ions. Current investigation provides a method to develop novel PVA/MOFs nanofibers hybrid adsorbents for water purification system. The adsorption capacities and removal achieved with the PVA/MOFs nanofibers sorbent were higher than those for PVA sorbent. The electro spun nanofiber sorbents presents an efficient alternative for pre-treating lead ions in aqueous solutions. Results from this research demonstrated that higher performance novel nanofibers, which possessed higher adsorption percentages and capacity capabilities were obtsained far exceeding some of the commonly used adsorbents, were obtained.

No description available.