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Electronic Structure and Reactivity of Bioinspired Organometallic Iron Complexes Relevant to Small Molecule ActivationKupper, Claudia Gisela 25 April 2017 (has links)
No description available.
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Understanding the Structure, Bonding and Reactivity of Unsaturated Metallacycles : A Computational StudyRoy, Subhendu January 2013 (has links) (PDF)
Stabilization of highly strained organic species and altering normal reactivity norms of organic fragments by transition metals have been a triumphing feat of organometallic chemistry. A variety of saturated and unsaturated metallacycles result from the reactions of the transition metals with the organic entities. Understanding the structure and bonding of the metallacylces has been indispensable over the years in view of its involvement as intermediates or compounds for numerous synthetic and catalytic applications. In this context, Group 4 metallocenes have unlocked a fascinating chemistry by stabilizing strained unsaturated C4 organic fragments in the form of five-membered metallacyclomulenes, metallacyclopentynes and metallacycloallnes. These molecules do not conform to the existing bonding principles of chemistry. We have carried out a comprehensive theoretical study to understand the unsual stability and reactivity of these metallacycles. Our theoretical study reveals that the unique interaction of the internal carbon atoms along with the terminal carbon atoms with the bent metallocene moiety is the reason for unsual stability of the metallacycles. We have also investigated the mechanism of interesting C-C coupling and cleavage reactions involving metallacyocumulenes. It demonstrates unexpected reaction pathway for these metallacycles. Moreover, based on this understanding, we have predicted and unraveled the stabilization factors of a challenging four membered metallcycloallene complex. Indeed, our prediction about a four-membered heterometallacycle has been realized experimentally. This kind of bonding is intriguing from fundamental perspective and has great relevance in synthesizing unsual structures with interesting properties. Finally, the electronic structure and bonding of a metallocene-alkyne complex is analyzed to determine the nature of bonding. Our aim is to build a conceptual framework to understand these metallacycles and to exploit their chemistry.
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Préparation et caractérisation de metallacalix[4]arenes supportes sur silice mésoporeuse pour la conversion des oléfines / Preparation and characterization of supported metallacalix[4]arenes onto mesoporous silica for the conversion of olefinsEspinas, Jeff 27 October 2010 (has links)
Elaboration de matériaux métallacalix[4]arènes pour la valorisation des hydrocarbures basée sur un nouveau concept de greffage par voie COMS dont la mise au point par fonctionnalisation de supports silice en faisant réagir l’hydroquinone avec une espèce originale [(SiO)2AliBu.(Et2O)]. La réactivité du complexe W(CtBu)(CH2tBu)3 avec l’hydroquinone supportée [(SiO)2AlO-C6H4-OH.(Et2O)] a permis de générer un nouveau système catalytique bien défini [(SiO)2AlO-C6H4-OW(CtBu)(CH2tBu)2.(Et2O)] entièrement caractérisé. Par cette méthode, l’ancrage du calixarène [[4H]-(OH)3(H)] sur le complexe de surface [(SiO)2AliBu.(Et2O)]SBA-15-(700) a conduit à l’espèce [(SiO)2Al-O-[4H]-(OH)2.(Et2O)]. L’incorporation de complexes organométalliques du groupe IV (Zr) et VI (W) mène à de nouveaux matériaux métallacalix[4]arènes bipodaux. L’élucidation de leurs structures a été appuyée par comparaison avec les données spectroscopiques de leurs homologues solubles ou directement liés à la silice. Ces matériaux, présentant des espaceurs phénoxy, montrent des activités initiales supérieures à celles de leurs homologues supportés sur silice. Avant la préparation des matériaux métallacalix[4]arènes, une série de complexes titana-, zircona- et tantalacalix[4]arenes solubles bi- et tripodaux a été synthétisée et caractérisée à partir de dérivés calix[4]arène présentant des modes de coordination différents pour le métal (podalité, ligands ancillaires, angle OMO). Parallèlement, une relation structure-réactivité dans la polymérisation des oléfines a été établie dans le cas des titanacalix[4]arènes, et pour les tantalacalix[4]arènes, des activations Csp2-H et O-Me intramoléculaires ont été mises en évidence. / Generation of novel metallacalix[4]arenes materials applied to the valorization of hydrocarbons prepared using an unprecendented COMS method by the first functionalization of the silica support by reaction of hydroquinone with the unreported supported species [(SiO)2AliBu.(Et2O)].The reactivity between the complex W(CtBu)(CH2tBu)3 and the hydroquinone species [(SiO)2AlO-C6H4-OH.(Et2O)] allows the access to new well-defined catalytic systems [(SiO)2AlO-C6H4-OW(CtBu)(CH2tBu)2.(Et2O)]. Using this way, the anchoring of the calixarene [[4H]-(OH)3(H)] onto [(SiO)2AliBu.(Et2O)]SBA-15-(700) leads to the surface complex [(SiO)2Al-O-[4H]-(OH)2.(Et2O)].The subsequent incorporation of organometallic complexes from groups IV (Zr) and VI (W) provided novel bipodal metallacalix[4]arenes materials, characterized by IR, solid-state NMR, microanalysis and EXAFS. The clarification of their structures was supported by comparison of the spectroscopic data collected from their soluble models or analogues directly bonded to silica. These new materials, presenting phenoxo linkers display higher initial conversion rates than their analogues directly grafted on silica. Before preparation of the materials, a set of bi and tripodal titana-, zircona- and tantalacalix[4]arenes complexes were synthesized and characterized from calix[4]arenes derivatives ligands, presenting different mode of coordination for the metal (podality, ancillary ligands, OMO bite angle). In parallel, a structure-reactivity relation in the polymerization of ethylene was established in the case of the titanacalix[4]arenes, while Csp2-H and O-Me intramolecular activations were related for the tantalacalix[4]arenes.
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Nouveaux oxydes métalliques supportés : vers la compréhension des catalyseurs industriels de métathèse des oléfines par une approche combinant synthèse, RMN et DFT / New supported metal oxo : towards the comprehension of industrial olefin metathesis catalysts via an integrated approach using on design synthesis, 17O NMR and DFT calculationBouhoute, Yassine 08 December 2016 (has links)
L'objectif de cette thèse était de préparer par voie chimie organométallique de surface de nouveaux complexes organométallique supportés portant des ligands oxo pour la métathèse des oléfines. La première approche consiste en l'utilisation d'un précurseur inorganique WOCl4 pour accéder en deux étapes à une espèce majoritaire bi-siloxy [(=SiO)2WOMe2] (80 %) active en métathèse de l'isobutène pour donner le 2,3-diméthylbutène. L'utilisation de précurseurs organotungstiques a permis de préparer et caractériser avec des techniques spectroscopiques (EXAFS, RAMAN, RMN Solide, DRIFT…) de nombreux complexes tungstènes oxo supportés avec des ligands spectateurs qui ont des réactivités variés. En effet, Un premier modèle du catalyseur industriel (=SiO)2W(=O)(CH2SiMe2)2 a été obtenu par réaction de greffage de [WO(CH2SiMe3)3Cl] sur une silice déshydroxylée à 200 °C. L'application de la RMN du solide de l'17O à l'étude structurale de cette espèce oxo de surface, combinée avec des calculs DFT montrent que deux structures, bipyramidale trigonale (TPB) et pyramide à base carrée (SP), peuvent co-exister en surface en raison de la faible barrière d'activation (< 5 kcal.mol-1). Cette nouvelle espèce de surface a montré une forte activité de 24 000 TON après 25 h avec une faible désactivation au cours du temps en métathèse du propène. Une approche originale pour la préparation des catalyseurs oxo de tungstène de structures [(=SiO)WO(CH2SiMe3)2OAr] a été développée et consiste en une simple modification de complexe monopodal supporté [(=SiO)WO(CH2SiMe3)3] par des phénols avec différents substituants en position ortho, ortho'. Les complexes supportés portant des ligands phénoxydes électroattracteurs se sont avérés plus actives et plus stable en métathèse du propène que leurs homologues portant des ligands phénoxydes riche en électrons. Ces différentes approches seront par la suite étendues au complexe de molybdène oxo alkyl / The aim of this thesis was to apply surface organometallic chemistry in order to prepare novel supported organometallic complexes bearing oxo ligands for olefin metathesis. The first approach consists of the utilization of an inorganic precursor (WOCl4) to obtain mainly (80%) the bis-siloxy species [(=SiO)2WOMe2] in two steps: grafting followed by alkylation with SnMe4. The latter material catalyzes isobutene self-metathesis to 2,3-dimethylbutene. Employing oxo organotungstene precursors results in materials that can be characterized by spectroscopic techniques (EXAFS, RAMAN, Solid-state NMR, DRIFT…) and offer a large variety to alter the spectator ligands. In fact, the first model of the industrial catalyst (=SiO)2W(=O)(CH2SiMe2)2 has been obtained by grafting of [WO(CH2SiMe3)3Cl] onto silica dehydroxylated at 200 °C. Elucidation of the surface structure by 17O MAS NMR along with DFT calculations suggest that there are most likely two co-existing geometries, trigonal bipyramidal (TPB) and square pyramide (SP), as the activation barrier is found to be low (<5 kcal.mol-1). This new surface species has shown a high activity in propene self-metathesis and low deactivation rate, at reflected by the high turn-over number of 24000 after 25 hours on stream. Furthermore, an original approach to access variety solid tungsten oxo catalysts expressed generally as [(=SiO)WO(CH2SiMe3)2OAr] has been developed and comprises a simple modification of the supported monopodal species [(=SiO)WO(CH2SiMe3)3] by desired phenol derivatives. Catalysts with electron withdrawing phenoxide ligands exhibit higher activity and stability in propene self-metathesis than their electron rich phenoxide homologue. The developed methodologies will be extended to molybdenum oxo alkyl complexes
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Redox Active Ligands To Facilitate Reactivity From Redox Restricted MetalsMatthew C Hewitt (11197530) 29 July 2021 (has links)
The synthesis of
metal-redox active ligand complexes is described, along with reactivity studies
aimed at facilitating novel C-N bond forming reactions. A copper
bis(iminosemiquinone) structure is characterized, analyzed and its reduction
series are characterized and the reactivity of the Cu(II) bis(amidophenolate)
analog is investigated with tosyl azide. The identification of the major
reaction product and its characterization is detailed, with reaction
sensitivities and heavily distorted x-ray diffraction single crystal structure
generating a complex data set. The characterization of the isolated product is
ongoing, with EPR studies aimed at identifying the radical nature of the
complex. Unusual solvent effects and solubility issues have been noted with
these initial EPR studies and more data is necessary before analysis can be
properly attempted. An ytterbium bis(amidophenolate) complex was synthesized
and its reactivity studied with aryl azides. Initial reactivities generate the
first documented lanthanide tetrazenes in-lieu of the targeted ytterbium imido.
Reactivities and characterization of these complexes support a stable, heavily
ionic tetrazene-metal complex with no observed redox nature, UV light
sensitivities, or imido azide-tetrazene equilibrium observed in various
tetrazene transition metal complexes. Synthesis of a sterically blocked ytterbium
imido was attempted, utilizing DMAP. Initial isolation was achieved with
characterization and reactivity studies supporting the imido nature of the
complex. The weak coordinating of the DMAP provided instability that proved in
opposition to crystallization, however, so the imido could not be confirmed.
Initial reactions using alternative steric hinderance from triphenylphosphine
oxide and pyridine N-oxide prove promising to increasing the stability of the
presumed ytterbium imido. Organic synthesis was performed generating a
potential antibacterial agent. The synthesis of cyclopropenes was initiated as
antagonists for ETR proteins in fruits and plants. The intermediates proved
highly sensitive to harsh chemical conditions, which was overcome utilizing a
tin-mediated Barbier allylation. The cyclopropene alcohol synthon was
synthesized, though protecting group optimization is necessary.
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Exploration of [2+2+2] cyclotrimerisation reactions of alkynes. A new methodology for the synthesis of small molecules to probe biological systemsNeves dos Santos, Ana Rita January 2013 (has links)
The generation of new chemical entities (NCEs) for use in chemical biology and drug discovery is of wide interest to both academia and the pharmaceutical industry. In order to generate NCEs, this project focused on development of new synthetic methodologies using transition-metal mediated [2+2+2] cyclotrimerisation of alkynes and unsaturated molecules to form bi- and tricyclic heterocyclic derivatives, some with structural resemblance to the quinocarcin family of natural products. Three different dialkynes (1,5-di(prop-2-yn-1-yl)pyrrolidin-2-one 2.117a, 1,6-di(prop-2-yn-1-yl)piperidin-2-one 2.118a and 4-benzyl-1,6-di(prop-2-yn-1-yl)piperazin-2-one 2.120a) were successfully synthesised. Several cyclotrimerisations were attempted, with the best yields being obtained when diethylacetylene dicarboxylate 2.113a was used as the monoalkyne and Cp*Ru(cod)Cl as the catalyst in refluxing toluene. New heterocyclic compounds with potential for diversification were synthesised using a diversity-oriented synthesis approach; specifically the build/couple/pair strategy for the synthesis of small molecules. Racemic nitrogen and oxygen building blocks were coupled with acrylonitrile, bromoacetonitrile and acyl chlorides. The pair step involved the intramolecular ring closure using transition-metal catalysed [2+2+2] cyclotrimerisations using microwave assisted radiation. The best catalyst for this approach was found to be CpCo(CO)2 at 150 ºC (300 W) in chlorobenzene. This provided a new methodology with potential for synthesising a diverse set of small molecules for biological testing. 20 compounds were subjected to chemosensitivity testing using the MTT assay. Several compounds were shown to possess activity in bladder (RT112) and breast (MCF-7) cancer cell lines. As these two cell lines are known to express extra-hepatic cytochromes P450 enzymes, it is possible that these are involved in generating cytotoxic metabolites that may damage DNA. / Fundação Para a Ciência e a Tecnologia (FCT)
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<b>Fundamental Inorganic Chemistry for Renewable Energy Resources: Highlights in Tellurium, Zirconium, Hafnium, and Neptunium Coordination Chemistry</b>Madeleine Claire Uible (19173208) 18 July 2024 (has links)
<p dir="ltr">The separation of tellurium from cadmium telluride is examined using a unique combination of mild, anhydrous chlorination and complexation of the subsequent tellurium tetrachloride with 3,5-di-<i>tert</i>-butylcatechol. The resulting tellurium complex, Te(dtbc)<sub>2</sub>, is isolated in moderate yield and features a 10<sup>3</sup> to 10<sup>4</sup> reduction in cadmium content, as provided by XRF and ICP-MS analysis. Similar results were obtained from zinc telluride. A significant separation between Te, Se, and S was observed after treating a complex mixture of metal chalcogenides with this protocol. These three tunable steps can be applied for future applications of CdTe photovoltaic waste.</p><p dir="ltr">We report the synthesis and characterization of the first series of tellurium and selenium complexes featuring an η<sup>5</sup>-cyclopentadienyl ligand. Reaction of Ph<sub>3</sub>TeX (X = Cl, S<sub>2</sub>CNEt<sub>2</sub>) with MCp<sup>R</sup> (M = Li, K; R = H, Me<sub>4</sub>, Me<sub>5</sub>) results in high yields of [Cp][TePh<sub>3</sub>] (<b>1</b>), [Cp<sup>Me4</sup>][TePh<sub>3</sub>] (<b>2</b>), and [Cp*][TePh<sub>3</sub>] (<b>3</b>), respectively. Similarly, reaction of Ph<sub>3</sub>SeCl with LiCp and KCp* furnishes [Cp][SePh<sub>3</sub>] (<b>4</b>) and [Cp*][SePh<sub>3</sub>] (<b>5</b>). Each was characterized by X-ray crystallography, revealing similar η<sup>5</sup>-coordination with little distortion from an idealized half-sandwich geometry, presumably from the remaining lone pair on tellurium and selenium. The Te–centroid distances are relatively long (<b>1</b>: 2.770(3), <b>2</b>: 2.746(1), and <b>3</b>: 2.733(1) Å), suggesting a mostly ionic interaction. Se–centroid distances (<b>4</b>: 2.748(3), <b>5</b>: 2.707(2), 2.730(2) Å) were found to be surprisingly similar despite its smaller atomic radius. Compounds <b>2</b>, <b>3</b>, and <b>5</b> display rapid decomposition at room temperature, extruding a phenylated cyclopentadiene and the and the respective diphenylchalcogenide. The nature of bonding within these complexes was investigated through DFT methods and found to be primarily ionic in nature.</p><p dir="ltr">Synthesis of homoleptic zirconium and hafnium dithiocarbamate via carbon disulfide insertion into zirconium and hafnium amides were investigated for their utility as soluble molecular precursors for chalcogenide perovskites and binary metal sulfides. Treating M(NEtR)<sub>4</sub> (M= Zr, Hf and R= Me, Et) with CS<sub>2</sub> resulted in quantitative yields of homoleptic Group IV dithiocarbamates. Zr(k<sup>2</sup>-S<sub>2</sub>CNMeEt) (<b>1</b>), Zr(k<sup>2</sup>-S<sub>2</sub>CNEt<sub>2</sub>)<sub>4</sub> (<b>2</b>), and Hf(k<sup>2</sup>-S<sub>2</sub>CNEt<sub>2</sub>)<sub>4 </sub>(<b>4</b>), a rare example of a crystal of a homoleptic hafnium CS<sub>2</sub> inserted amide species, were characterized. A computational analysis confirmed assignments for IR spectroscopy.<b> </b>To exemplify the utility of the Group IV dithiocarbamates, a solution-phase nanoparticle synthesis was performed to obtain ZrS<sub>3</sub> via the thermal decomposition of Zr(S<sub>2</sub>CNMeEt)<sub>4</sub></p><p dir="ltr">Chalcogenide perovskites have garnered interest for applications in semiconductor devices due to their excellent predicted optoelectronic properties and stability. However, high synthesis temperatures have historically made these materials incompatible with the creation of photovoltaic devices. Here, we demonstrate the solution processed synthesis of luminescent BaZrS<sub>3</sub> and BaHfS<sub>3</sub> chalcogenide perovskite films using single-phase molecular precursors at sulfurization temperatures of 575 °C and sulfurization times as short as one hour. These molecular precursor inks were synthesized using known carbon disulfide insertion chemistry to create Group 4 metal dithiocarbamates, and this chemistry was extended to create species, such as barium dithiocarboxylates, that have never been reported before. These findings, with added future research, have the potential to yield fully solution processed thin films of chalcogenide perovskites for various optoelectronic applications.</p><p dir="ltr">Np(IV) Lewis base adducts were prepared by ligand substitution of NpCl<sub>4</sub>(DME)<sub>2</sub>. Using acetonitrile and pyridine, NpCl<sub>4</sub>(MeCN)<sub>4</sub> (<b>1</b>) and NpCl<sub>4</sub>(pyr)<sub>4</sub> (<b>2</b>), were isolated, respectively. All species were fully characterized using spectroscopic and structural analyses.</p>
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Binucleating Ligands: Design and ReactivityMichael Behlen (8703033) 21 June 2022 (has links)
<div><div><div><p>Pincer ligands are a cornerstone of modern transition metal catalysis. An increasing interest in bimetallic catalysis motivated us to develop binucleating variants of these mononucleating ligands. Expanded variants of the PDI and PyBOX ligands were targeted, leading to the development of the Naphthyridine Diimine (“NDI”) and Naphthyridine Bisoxazoline (“NapBOX”) ligands, respectively. Metalation of NDI with appropriate metal precursors yielded Fe2, Co2 and Ni2 complexes which exhibited unique stoichiometric and catalytic reactivity. Metalation of the NapBOX ligand with nickel carboxylate salts yielded Ni2 complexes which were capable of catalyzing an asymmetric intermolecular [4+1] cycloaddition reaction between 1,1-dichloroalkene-derived vinylidenes and 1,3-dienes. Each of these processes were studied experimentally and computationally in order to understand the fundamental reactivity of organic substrates across metal-metal bonds.</p></div></div></div>
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Alkaline earth- and rare earth-transition metal complexesBlake, Matthew Paul January 2013 (has links)
This Thesis describes the synthesis and characterisation of new alkaline earth- and rare earth-transition metal complexes. Experimental and computational studies were performed to investigate the structure and bonding in these complexes. Their reactivity was also studied. Chapter 1 introduces metal-metal bonded complexes and current alkaline earth- and rare earth-transition metal bonded complexes. Chapter 2 describes experimental and computational studies of new alkaline earth- and lanthanide-Fe complexes possessing the [CpFe(CO)2]- anion. Chapter 3 presents experimental studies of the reduction of Fe3(CO)12 with Ca. Chapter 4 describes experimental and computational studies of new alkaline earth- and lanthanide-Co complexes containing the [Co(CO)3(PR3)]- anion. Chapter 5 presents full experimental procedures and characterising data for the new complexes reported. Appendix describes the attempted synthesis of [Ca{CpRu(CO)2}2(THF)x]y and study by DFT of [CaRp2(THF)3]2 CD Appendix contains .cif files for all new crystallographically characterised complexes described.
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Preparation and characterisation of encapsulation magnetic metal iron oxide nanoparticlesAl-Saadi, Ali January 2012 (has links)
One of the most challenging goals in nanoparticle research is to develop successful protocols for the large-scale, simple and possibly low-cost preparation of morphologically pure nanoparticles with enhanced properties. The work presented in this thesis was focused on the synthesis, characterisation and testing of magnetic nanoparticles and their potential applications. There are a number of magnetic nano-materials prepared for specific applications such as metal oxide nanoparticles encapsulated with various porous materials including Fe₃O₄/Fe₂O₃ coated with soft bio-organic materials such as glycol chitosan and bovine serum albumin and hard materials such as silica (SiO₂) and zinc sulphide (ZnS). The preparation of these materials was achieved principally by bottom-up methods with different approaches including micro-emulsion, precipitation, electrostatic and thermolysis processes. The thesis also presents the uses of various analytical techniques for characterising different types of nano-materials including Attenuated Total Reflection Fourier Transformer Infrared Vibrational Spectroscopy (ATR-FTIR), Ultraviolet Visible- Near Infrared (UV-Vis-NIR) Spectroscopy, Zeta Potentiometric Surface Charge Analysis, Superconducting Quantum Interference Device (SQUID) and Vibration Sample Magnetometry (VSM) for magnetic analysis and powder X-Ray Diffraction (XRD) for crystallographic pattern analysis. There are many applications of magnetic nanoparticles, including nano-carriers for biological and catalytic reagents. The magnetic nanoparticles can facilitate separation in order to isolate the carriers from solution mixtures as compared to many inefficient and expensive classic methods, which include dialysis membrane, electrophoresis, ultracentrifugation, precipitation and column separation methods. There are six key chapters in this thesis: the first chapter introduces the up-to-date literature regarding magnetic nano-materials. The uses of magnetic nano-materials in drug binding and for protein separation are discussed in the second and third chapters. The fourth chapter presents the use of magnetic nanoparticle in conjunction with a photo-catalytic porous overlayer for the photo-catalytic reduction of organic molecules. The fifth chapter describes different analytical techniques used for the characterisation of nanoparticles and the underlying principles and the experimental details are also given. The sixth chapter summarises the results and provides an overview of the work in a wider context of future applications of magnetic nanoparticles.
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