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1
Rodrigo, Sanjeewa K. « Nickel Catalyzed Regioselective Reductive Coupling Reactions ». University of Cincinnati / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1396532622.
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Börjesson, Carazo Marino Rolando. « Ni-Catalyzed Reductive Carboxylation Reactions with Carbon Dioxide ». Doctoral thesis, Universitat Rovira i Virgili, 2020. http://hdl.handle.net/10803/670249.
Texte intégralRésumé :
El gas hivernacle principal emès a causa del desenvolupament industrial de la nostra societat és el diòxid de carboni. Com a conseqüència, els darrers anys han estat testimonis del desenvolupament de processos per a la fixació de CO2 en molècules orgàniques. Tot i que l’ús químic del CO2 probablement no reduirà dràsticament la seva concentració a l’atmosfera, el seu baix cost i alta disponibilitat podria ajudar a substituir alguns dels processos industrials establerts que contribueixen al canvi climàtic. En particular, el grup carboxil està present en una gran quantitat de productes farmacèutics, agroquímics o plàstics, entre d’altres, fent de la seva síntesi un objectiu ideal per a l’ús químic de CO2. A diferència de les carboxilacions tradicionals de reactius organometàlics altament polaritzats i sensibles, les reaccions de carboxilació reductiva ofereixen la possibilitat d'utilitzar electròfils simples, representant una alternativa formidable, conceptualitat i practicitat a part, per a aquestes entitats nucleífiques.
Aquests estudis de doctorat s’han centrat en el desenvolupament i la comprensió de noves, senzilles i pràctiques reaccions reductives de carboxilacions per produir àcids carboxílics a partir d’electròfils barats i abundants mitjançant la catàlisi Níquel.El principal gas de efecto invernadero emitido debido al desarrollo industrial de nuestra sociedad es el dióxido de carbono. Como consecuencia, los últimos años han sido testigos del desarrollo de procesos para la fijación de CO2 en moléculas orgánicas. Aunque la utilización química del CO2 probablemente no reducirá drásticamente su concentración en la atmósfera, su bajo costo y alta disponibilidad podrían ayudar a reemplazar algunos de los procesos industriales establecidos que contribuyen al cambio climático. En particular, el grupo carboxilo está presente en una gran cantidad de productos farmacéuticos, agroquímicos o plásticos, entre otros, lo que hace que su síntesis sea un objetivo ideal para la utilización de CO2. A diferencia de las carboxilaciones tradicionales de reactivos organometálicos sensibles altamente polarizados, las reacciones de carboxilación reductora ofrecen la posibilidad de emplear electrófilos simples, que representan una formidable alternativa, conceptualidad y practicidad a un lado, para tales entidades nucleofílicas. Estos estudios de doctorado se han centrado en el desarrollo y la comprensión de reacciones de carboxilaciones reductoras nuevas, simples y prácticas para producir ácidos carboxílicos a partir de electrófilos económicos y abundantes mediante catálisis de Níquel.
The primary greenhouse gas emitted due to the industrial development of our society is carbon dioxide. As a consequence, the recent years have witnessed the development of processes for the fixation of CO2 into organic molecules. Although the chemical utilization of CO2 will most likely not dramatically reduce its concentration in the atmosphere, its low cost and high availability could potentially help replace some of the established industrial processes that contribute to climate change. In particular, the carboxylic acid motif is present on a myriad of pharmaceuticals, agrochemicals or plastics, among others, making their synthesis an ideal target for CO2 chemical utilization. Unlike traditional carboxylations of highly polarized, sensitive organometallic reagents, reductive carboxylation reactions offer the possibility to employ simple electrophiles, representing a formidable alternative, conceptuality and practicality aside, to such nuclephilic entities. These doctoral studies have focused on the development and understanding of new, simple and practical reductive carboxylations reactions to produce carboxylic acids from inexpensive and abundant electrophiles by means of Ni-catalysis.
3
Serrano, Robledo Eloísa Sofía. « Amide Formation via Ni-Catalyzed Reductive Coupling Reactions with Isocyanates ». Doctoral thesis, Universitat Rovira i Virgili, 2018. http://hdl.handle.net/10803/586084.
Texte intégralRésumé :
Recentment, les reaccions d’acoblament creuat entre electròfils s’han posicionat com a potents alternatives a les reaccions clàssiques d’acoblament creuat entre electròfils orgànics i nucleòfils organometàl•lics. Aquests acoblaments reductius presenten nombrosos avantatges degut a que utilitzen compostos de partida simples i fàcilment assequibles que eviten la necessitat de sintetitzar espècies organometàl•liques sensibles a la humitat i a l’oxigen. Com a conseqüència, els protocols experimentals són pràctics i les condicions de reacció són suaus. A causa de la ubiqüitat de les amides en molècules biològicament actives tals com pèptids, agroquímics, productes farmacèutics o materials sintètics, s’ha impulsat un continu desenvolupament de nous mètodes eficients basats en la síntesis d’amides. La present tesis doctoral, està centrada en el desenvolupament de nous acoblaments reductius creuats catalitzats per níquel per la síntesis d’amides utilitzant isocianats com a sintons. Concretament, es presenta i es desenvolupa un nou protocol destinat a la síntesis d’amides alifàtiques a partir de bromurs d’alquil primaris, secundaris i terciaris combinats amb isocianats d’aril o d’alquil. Tanmateix, s’inclou el desenvolupament d’una metodologia per la hidroamidació altament diastereoselectiva d’alquins ans isocianats per la formació d’acilamides. Aquest protocol utilitza bromurs d’alquil com a font per la formació d’hidrurs in situ. Finalment, es presenta una discussió dels resultats preliminars sobre l’amidació regiodivergent, retentiva i remota de bromurs d’alquil secundaris inactius. Les transformacions desenvolupades aquí constitueixen nous mètodes per la síntesi d’amides mitjançant la formació d’enllaços C-C catalitzada per metalls i es caracteritza per les condicions suaus, l’ampli abast de la reacció, la seva excel•lent regioselectivitat i alta tolerància amb diversos grups funcionals.Recientemente, las reacciones de acoplamiento cruzado entre electrófilos se han posicionado como potentes alternativas a las reacciones clásicas de acoplamiento cruzado entre electrófilos orgánicos y nucleófilos organometálicos. Dichos acoplamientos reductivos ofrecen numerosas ventajas, ya que utilizan compuestos de partida simples y fácilmente asequibles que evitan la necesidad de sintetizar especies organometálicas sensibles a la humedad y al oxígeno. Debido a ello, los protocolos experimentales son prácticos y las condiciones de reacción suaves. La ubiquidad de las amidas en moléculas biológicamente activas tales como péptidos, agroquímicos y productos farmacéuticos, así como en materiales sintéticos, impulsa continuamente el desarrollo de nuevos métodos para la síntesis eficiente de amidas. La presente Tesis Doctoral, se centra en el desarrollo de nuevos acoplamientos reductivos cruzados catalizados por níquel para la síntesis de amidas, utilizando isocianatos como el sintón correspondiente a la amida. Específicamente, se presenta un nuevo protocolo para la síntesis de amidas alifáticas a partir de bromuros de alquilo primarios, secundarios y terciarios en combinación con isocianatos de arilo y alquilo. Asimismo, se incluye el desarrollo de una metodología para la hidroamidación altamente diastereoselectiva de alquinos con isocianatos para la formación de acrilamidas. Dicho protocolo utiliza bromuros de alquilo como fuentes suaves para la formación de hidruros in situ. Finalmente, se discuten resultados preliminares sobre la amidación regiodivergente, retentiva y remota, de bromuros de alquilo secundarios inactivados. Las transformaciones desarrolladas aquí constituyen nuevos métodos para la síntesis de amidas mediante la formación de enlaces C-C catalizada por metales y se caracterizan por sus condiciones suaves, su amplio alcance de reacción, su excelente regioselectividad y alta tolerancia a diversos grupos funcionales.
Recently, cross-electrophile couplings have become powerful alternatives to classical cross-coupling reactions that are based on nucleophile/electrophile regimes. Starting from readily available building blocks, reductive couplings are practical and mild protocols that circumvent the use of moisture and air-sensitive organometallic species. The ubiquity of amides in biologically relevant molecules such as peptides, agrochemicals and pharmaceuticals, as well as in polymers, continually prompts the design of novel methods for amide synthesis. This Doctoral Thesis focuses on the development of novel nickel-catalyzed reductive protocols for the synthesis of amides using isocyanates as the amide synthon. Specifically, we have discovered a novel protocol for the synthesis of aliphatic amides from primary, secondary and tertiary alkyl bromides in combination with aryl and alkyl isocyanates. A methodology for the highly diastereoselective hydroamidation of alkynes with isocyanates to afford acrylamides has been developed, with alkyl bromides used as in situ and mild hydride sources. Finally, efforts towards the regiodivergent retentive and chain-walking amidation of unactivated acyclic secondary alkyl bromides are discussed. The transformations developed herein are characterized by their mild conditions, wide substrate scope and excellent chemo- and regioselectivity, and constitute novel methods for the formation of amides via metal-catalyzed C—C bond formation.
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Joensuu, Pekka Matias. « Development of catalytic stereoselective reductive aldol reactions ». Thesis, University of Edinburgh, 2008. http://hdl.handle.net/1842/2576.
Texte intégralRésumé :
The chemistry of enolates can be considered one of the cornerstone areas in organic chemistry. Regioselective generation of an enolate in the presence of several enolisable sites can often prove to be a difficult task. Discoveries in recent years have led to new areas of enolate formation in the presence of other carbonyl groups. These include reductive aldol chemistry where direct reductive aldol coupling of an alpha,beta - unsaturated carbonyl group in presence of a carbonyl electrophile enables often perfectly regioselective reactions to occur. This tandem conjugate reductionelectrophilic trapping process enables the reaction to be performed in a “one-pot” manner. The first examples of asymmetric copper-catalysed reductive aldol reactions have been developed for the formation of a range of beta-hydroxylactone products. A combination of Cu(OAc)2.H2O with different bisphosphine ligands catalyses these intramolecular reductive aldol reactions. TMDS (1,1,3,3-tetramethylhydrosiloxane) is used as a stoichiometric hydride source. The reaction proceeds with high relative stereocontrol (>19:1 dr), while absolute stereocontrol remains modest (up to 83% ee). The yields range from moderate to good. A continuous search for improved reaction conditions led to the discovery that cobalt-catalysed reductive aldol reactions have an advantage over the coppercatalysed reaction in the cases where 4-hydroxypiperidin-2-one products are formed. When Co(acac)2·H2O is used together with Et2Zn as the stoichiometric reductant, an increased substrate scope is observed while the diastereoselectivity of the reaction remains high. Yields are also remarkably higher compared to the results obtained with the copper catalyst. These reaction conditions are also used to perform intermolecular reductive aldol reactions between a range of alpha,beta-unsaturated amides and ketones. The reactions proceed readily with high diastereoselectivities (up to >19:1 syn:anti) and good yields. Asymmetric variants have been studied by the use of a chiral oxazolidine auxiliary. Although good selectivities have been obtained, this method currently suffers from the fact that the chiral auxiliary is difficult to cleave. Ni(acac)2 was also found to perform the intramolecular reductive aldol reaction. Et2Zn was again used as the stoichiometric reductant. The nickel-catalysed reaction increased the reaction scope still further. This time both beta-hydroxylactone and 4-hydroxypiperidin-2-one products were readily formed. The former proceeded with increased yields compared to those obtained with the copper catalyst, and, the latter with comparable results to those obtained with the cobalt catalyst.
5
Gallagher, P. « The reductive decomposition of bis-diazo-alkanes ». Thesis, University of Liverpool, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381343.
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Mc, Geehin Peter Kevin Mark. « Hydrogenation, hydrogenolysis and reductive fission reactions of cis dihydrodiols ». Thesis, Queen's University Belfast, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252284.
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Chakraborty, Satyajit. « Studies on oxidative and reductive reactions of carbocyclic compounds ». Thesis, University of North Bengal, 1988. http://hdl.handle.net/123456789/709.
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Fung, Chi-ming Kelvin. « Synthesis and applications of copper hydride complexes in reductive reactions ». Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B36388208.
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Fung, Chi-ming Kelvin, et 馮志明. « Synthesis and applications of copper hydride complexes in reductive reactions ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B36388208.
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Mendiratta, Arjun. « Reductive coupling and related reactions with Mo and Ti tris- anilides ». Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32483.
Texte intégralRésumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2005.Vita.
Includes bibliographical references.
Chapter 1: The capability of Mo(N[t-BulAr)₃ to act as a powerful one, two, and three electron reductant have been previously demonstrated. In this work, we show that Mo(NIt-BulAr)₃ forms a metastable adduct with the moderate [pi] acid PhCN; coordination of PhCN activates the nitrile carbon towards reaction with a variety of one-electron reagents such as dichalcogenides, nitric oxide, hydrogen atom donors, cobaltocene, and elemental phosphorus. Evidence is presented for the existence of an inner-sphere electron transfer mechanism for these reactions. Chapter 2: With the facile cleavage of N₂ by Mo(Njt-Bu]Ar)₃ already established, a Mo(NIt-Bu]Ar)₃-mediated process for the incorporation of N₂ into organic molecules is an exciting prospect; its realization depends critically on the development of methods for cleavage of the Mo-N bond formed in the early stages of the process. In this chapter, we demonstrate that appropriately-substituted Mo(IV) ketiminates (synthesized using the methods of Chapter 1) undergo [beta]-elimination to cleave the Mo-N bond and liberate PhCN. We present the kinetics of the reaction, substituent effects, and-in three cases - activation parameters. Chapter 3: Deprotonation of the titanium formate complex (ArIt-BuJN)₃TiOC(O)H with LiN(i-Pr)₂ resulted in the release of free CO and the formation of a titanium(IV) oxoanion complex, isolated as its lithium salt. Chapter 4: Previous work from these labs has shown that the unique combination of well-defined composition, steric bulk, and strong reducing ability embodied in Ti(N[t- Bu]Ar)₃ lends itself particularly well to mechanistic studies of the classical Pinacol coupling.
(cont.) As shown in Chapter 1, a similar relationship can be drawn between Mo(NIt- BulAr)₃ and reductive nitrile coupling. In this chapter we draw on this mechanistic understanding to develop three new classes of reductive cross-couplings: nitrile is coupled with pyridine to form dihydropyridines, with benzophenone to form substituted 1,4-cyclohexadienes, and with carbon dioxide to form a-iminocarboxylates.
by Arjun Mendiratta.
Ph.D.
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Lumby, Ralph James Richard. « Novel transition-metal-catalysed reactions using diethylzinc as the stoichiometric reductant ». Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/3890.
Texte intégralRésumé :
Modern organic chemistry strives to achieve rapid molecular complexity from simple achiral substrates. One method by which this may be achieved is with enolate formation followed by attack on an electrophile which can generate one, two or even more new stereocentres in one step. However regioselective generation of an enolate in the presence of several enolisable sites has always proved problematical. A partial answer to this problem has been provided by the development of the reductive aldol reaction. The first part of this thesis is concerned with describing a highly diastereoselective Co(II)-catalysed reductive aldol reaction between α,β-unsaturated amides and ketones. The reaction proceeds using substoichiometric quantities of cobalt(II) in the presence of a stoichiometric quantity of the reductant diethylzinc. Using both N,Ndimethyl and morpholine amides, the reactions are tolerant of substituted aromatic ketones as well as aliphatic ketones. The reaction also proceeded well when the β-carbon was substituted with both aromatic and aliphatic groups resulting in improved diastereoselection. The racemic work is followed by the development of an asymmetric version of the reaction using oxazolidinone chiral auxiliaries that impart high levels of diastereofacial selectivity. The reaction was found to proceed with a variety of aromatic ketones and once again, substitution of the β-carbon resulted in improved diastereoselectivity. Finally work on formal homo aldol cyclisations using substoichiometric quantities of Ni(II) also in the presence of a stoichiometric quantity of diethylzinc is described. This work aims to develop methodology that involves double cyclisations with the formation of up to five contiguous stereocentres. Although unsuccessful, useful conclusions for future work were made as well as the serendipitous discovery of a apparent base catalysed alternative cyclisation pathway that successfully generated two new rings and four contiguous stereocentres.
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Leung, Sze-kar, et 梁詩嘉. « Novel reactions of oxabicyclic compounds and reductive aldol cyclizations of activated alkynes ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B44570156.
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Mork, Anna Jolene. « Novel reactions of a neutral organic reductant : reductive coupling and nanoparticle synthesis ». Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/73438.
Texte intégralRésumé :
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2012.Vita. Cataloged from PDF version of thesis.
Includes bibliographical references (p. 53-55).
A recently developed bis-pyridinylidene neutral organic electron donor captured our interest as a potential source of new chemistries for reductive coupling and the synthesis of group IV nanoparticles. This super electron donor was used as a co-reductant for nickel-catalyzed reductive coupling of aryl halides in order for the reaction to be homogeneous and avoid the traditional co-reductant, zinc, previously reported for these Yamamoto-type dehalogenative couplings. Reductive coupling was somewhat successful for specific substrates, including 4- bromoanisole and 2,5-dibromothiophene, but competing hydrodehalogenation of the aryl halide was problematic for both expanding the substrate scope and increasing the length of the polymers generated from this reaction. The attempt to synthesize silicon and germanium nanoparticles from reduction of the corresponding tetrachloride precursors using this super organic electron donor met limited success. Dimerization of silicon species occurred, but there was little conclusive evidence of nanoparticle formation. Finally, in a brief side-project to explore other applications of the organic reductant, the molecule was shown to successfully n-dope both p-type and n-type organic electronic materials.
by Anna Jolene Mork.
S.M.
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RAMADAN, DOAA REDA MOHAMED. « PALLADIUM CATALYZED REACTIONS : REDUCTIVE CYCLIZATION OF NITROARENES, AND OXIDATIVE CARBONYLATION OF ANILINE ». Doctoral thesis, Università degli Studi di Milano, 2021. http://hdl.handle.net/2434/819652.
Texte intégralRésumé :
Palladium Catalyzed Reactions: Reductive Cyclization of Nitroarenes, and Oxidative Carbonylation of Aniline
Abstract:
The thesis is divided into two main chapters: reductive cyclization of nitroarenes, and oxidative carbonylation of aniline.
The first chapter involves developing a catalytic system for carbazoles synthesis through reductive cyclization of 2-nitrobiphenyls employing phenyl formate as an in-situ source of CO. Thus, the synthetic chemist can avoid handling pressurized CO lines and perform the reaction in a pressure tube, a cheap and readily available tool for any laboratory. Moreover, the developed protocol can tolerate both air and moisture and can be performed using undried and undistilled commercial DMF. Several carbazoles bearing a wide range of substituents were synthesized in good to excellent yields including some with valuable pharmaceutical or thermo/electrical applications. The reaction could be performed on the grams scale affording carbazole in a very good yield (85%) without the need for chromatographic purification, making our synthetic strategy even more attractive and economically advantageous.
The second chapter deals with the palladium/iodide couple which is the most investigated catalytic system for the oxidative carbonylation of amines to give ureas or carbamates. In reinvestigating it, we found that the most prominent role of iodide is to etch the stainless steel of the autoclave employed in most of previous works, releasing in solution small amounts of iron salts. The latter are much better promoters than iodide itself. Iron and iodide have a complex interplay and, depending on relative ratios, can even deactivate each other. The presence of a halide is beneficial, but chloride is better than iodide in this respect. The ideal Fe/Pd ratio is around 10, but even an equimolar amount of iron with respect to palladium (0.02 mol% with respect to aniline, corresponding to 12 ppm Fe with respect to the whole solution) is sufficient to boost the activity of the catalytic system. Such small amount may also come from Fe(CO)5 impurities present in the CO gas when stored in steel tanks. The role of the solvent has also been investigated. It was found that the reason for the better selectivity in some cases is at least in part due to a hydrolysis of the solvent itself, which removes the coproduced water.
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Ray, Tandra. « Chemical studies on natural products : isolation, characterisation and oxidative and reductive reactions ». Thesis, University of North Bengal, 1991. http://hdl.handle.net/123456789/851.
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Fava, Eleonora [Verfasser]. « Visible light mediated photoredox catalysis : reductive carbon-carbon bond forming reactions / Eleonora Fava ». München : Verlag Dr. Hut, 2015. http://d-nb.info/1079768645/34.
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Moslin, Ryan Thomas McLeod. « Nickel-catalyzed reductive coupling reactions of 1,6-enynes and the total synthesis of (+)-acutiphycin ». Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/38622.
Texte intégralRésumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2007.Vita.
Includes bibliographical references.
Nickel-Catalyzed Reductive Coupling Reactions of Aldehydes and Chiral 1,6-Enynes. A study of nickel-catalyzed reductive coupling reactions of aldehydes and chiral 1,6-enynes has provided evidence for stereospecific ligand substitution from a planar three-coordinate nickel species as a plausible explanation of regioselectivity in the nickel-catalyzed reductive coupling of aldehydes and 1,6-enynes. In the absence of a phosphine additive, high regioselectivity and high diastereoselectivity are obtained as a direct result of coordination of both the alkyne and the olefin to the metal center during the C-C bond-forming step. ... Total Synthesis of (+)-Acutiphycin. Synthetic studies toward the total synthesis of (+)-acutiphycin led to, and were in turn further developed by, the study of nickel-catalyzed reductive coupling reactions of 1,6-enynes and aldehydes. ... Ultimately, though not employing the nickel-catalyzed reaction, a highly convergent total synthesis of (+)-acutiphycin featuring an intermolecular SmI2-mediated Reformatsky coupling reaction and macrolactonization initiated by a retro-ene reaction of an alkoxyalkyne was developed. The resulting synthesis was 18 steps in the longest linear sequence from either methyl acetoacetate or isobutyraldehyde. ...
by Ryan Thomas McLeod Moslin.
Ph.D.
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Shi, Weiwei. « Kinetic and spectroscopic characterization of the reductive and oxidative half-reactions of trimethylamine dehydrogenase ». Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1085107954.
Texte intégralRésumé :
Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xvii, 215 p.; also includes graphics (some col.) Includes bibliographical references (p. 208-215). Available online via OhioLINK's ETD Center
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Woodin, Katrina Sue. « Nickel-catalyzed reductive coupling reactions : application to the total syntheses of pumiliotoxins 209F and 251D ». Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/38625.
Texte intégralRésumé :
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2007.Vita.
Includes bibliographical references.
Catalytic Asymmetric Reductive Coupling of 1,3-Enynes and Aromatic Aldehydes Nickel-catalyzed reductive coupling reactions of 1,3-enynes and aromatic aldehydes efficiently afford conjugated dienols in excellent regioselectivity and modest enantioselectivity. These reactions were conducted in the presence of a catalytic ligand (R)-ferrocenyl(2-isopropylphenyl)phenylphosphine, whose overall synthesis was improved during the course of this investigation. 1-(Trimethylsilyl)-substituted enynes are shown to be efficient coupling partners in these reactions, and the dienol products formed readily undergo protiodesilylation under mild conditions. ... Catalytic, Asymmetric, Intramolecular Reductive Coupling of 1,1-Disubstituted Epoxides and Alkynes: Total Synthesis of Pumiliotoxin 209F and 251D Pumiliotoxins 209F and 251 D were prepared using a novel nickel-catalyzed intramolecular cyclizations between alkynes and 1,1-disubstituted epoxides. These cyclizations formed exclusively endo products without the use of a directing group on the alkyne. The synthesis of the reductive coupling precursors involved a diastereoselective sulfur ylide epoxidation of a proline-derived methyl ketone, where the choice of sulfonium salt conferred a major effect on the diastereoselectivity.
by Katrina Sue Woodin.
S.M.
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Crumpton, Dawn M. « Mechanistic studies of carbon-carbon and carbon-hydrogen reductive elimination reactions from platinum(IV) complexes / ». Thesis, Connect to this title online ; UW restricted, 2000. http://hdl.handle.net/1773/8484.
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Lau, Chi-yin. « Reductive aldol cyclizations using Stryker's reagent and polystyrene-supported triphenylarsine in carbon-carbon bond forming reactions ». Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/hkuto/record/B39634450.
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Lau, Chi-yin, et 劉志賢. « Reductive aldol cyclizations using Stryker's reagent and polystyrene-supported triphenylarsine in carbon-carbon bond forming reactions ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39634450.
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Petzold, Daniel [Verfasser], et Burkhard [Akademischer Betreuer] König. « Visible Light Mediated Oxidative Halogenation Reactions and Reductive Liberation of Fluorophosgene / Daniel Petzold ; Betreuer : Burkhard König ». Regensburg : Universitätsbibliothek Regensburg, 2020. http://d-nb.info/1210701987/34.
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Ericsson, Cecilia. « Synthesis of Tetrahydrofuran and Pyrrolidine Derivatives Utilising Radical Reactions : Organochalcogenides in Reductive, Carbonylative and Group-Transfer Cyclisation ». Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4018.
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Ban, Zhihui. « Synthesis and investigation of nanomaterials by homogeneous nonaqueous solution phase reactions ». ScholarWorks@UNO, 2005. http://louisdl.louislibraries.org/u?/NOD,274.
Texte intégralRésumé :
Thesis (Ph. D.)--University of New Orleans, 2005.Title from electronic submission form. "A dissertation ... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Chemistry"--Dissertation t.p. Vita. Includes bibliographical references.
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Reyes-Rodriguez, Efrain [Verfasser], et von Wangelin Axel [Akademischer Betreuer] Jacobi. « Manganese, Iron and Cobalt Catalyzed Reductive Hydrogenation and Cross-Coupling Reactions / Efrain Reyes-Rodriguez ; Betreuer : Axel Jacobi von Wangelin ». Regensburg : Universitätsbibliothek Regensburg, 2020. http://d-nb.info/1203874863/34.
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Wang, Shengdong. « Transition metal-catalyzed reduction reactions adding value to bio-sourced compounds ». Thesis, Rennes 1, 2018. http://www.theses.fr/2018REN1S134.
Texte intégralRésumé :
Le travail de recherche concerne l'utilisation de catalyseurs à base de métaux de transition: ruthénium, iridium, cobalt, argent, pour la transformation de substrats bio-sourcés renouvelables en produits à valeur ajoutée pour l'industrie chimique et l'énergie. La transformation par transfert d'hydrogène de l'acide lévulinique en γ-valérolactone a d'abord été développée avec de nouveaux catalyseurs du ruthénium et de l'iridium porteurs d'un ligand dipyridylamine et d'un chlorure en utilisant l'acide formique comme source d'hydrogène. Puis de nouveaux catalyseurs zwitterioniques de type ruthénium et iridium(sulfato)(dipyridylamine) ont été préparés et ils ont conduit aux meilleures productivités observées pour la réduction de l'acide lévulinique en γ-valérolactone par hydrogénation directe. Sur la base des excellentes performances des complexes iridium(sulfato)dans des processus de réduction, l'amination réductrice de l'acide lévulinique et de l'acide o-formylbenzoïque a été réalisée et a permis la synthèse efficace de dérivés de type pyrrolidones, en particulier à partir d'amines primaires encombrées. La déshydrogénation sélective de l'acide formique dans des conditions douces sans additif en milieu aqueux ou en absence de solvant a été développée avec les mêmes types de catalyseurs de l'iridium porteurs du ligand modifié diméthylaminodipyridylamine. Finalement, une méthode d'hydrogénation douce de cétones a été mise en évidence en présence d'un système catalytique à base de nanoparticules d'argent générées in situ. Ce système catalytique permet d'obtenir de bonnes efficacité et sélectivité vis-à-vis d'autre groupement fonctionnelsThis research work deals with the use of catalysts based on transition metals, such as ruthenium, iridium, cobalt, silver for transformations of renewable bio-based substrates to valuable products for applications in chemical industry and energy. The transfer hydrogenation of levulinic acid to γ-valerolactone with novel ruthenium- and iridium(dipyridylamine)chloride complexes using formic acid as hydrogen source was first developed. Then, novel zwitterionic ruthenium and iridium(sulfato)(dipyridylamine) catalysts were prepared, which displayed the highest turnover numbers reported for the reduction of levulinic acid into γ valerolactone using H₂ as hydrogen source. Based on the high catalytic performance of the iridium(sulfato)complexes in reduction processes, the efficient reductive amination of levulinic acid and o formylbenzoic acid, in particular with bulky primary amines, for the synthesis of pyrrolidone derivatives was disclosed. The selective dehydrogenation of formic acid under mild conditions in aqueous media or neat conditions without using an organic additive has been developed using iridium catalysts of the same family equipped with a modified dimethylaminodipyridylamineas ligand. Finally, an unprecedented hydrogenation of ketones in the presence of in situ generated silvernanoparticleswas discovered. High efficacy and functional group selectivity have been achieved in most cases
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Colby, Davie Elizabeth A. (Elizabeth Anne). « Enantioselective nickel-catalyzed reductive coupling reactions of alkynes and aldehydes. Synthesis of amphidinolides T1 and T4 via catalytic, stereoselective macrocyclizations ». Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32487.
Texte intégralRésumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2005.MIT Science Library copy: 2 v. set, in leaves.
Also issued in leaves, 2 v. set. Vita.
Includes bibliographical references.
I. Enantioselective Nickel-Catalyzed Reductive Couplings of Alkynes and Aldehydes Allylic alcohol synthesis via a nickel-catalyzed reductive coupling reaction of alkylsubstituted alkynes and aldehydes was studied for ligand effects with respect to the regioselectivity and enantioselectivity of the coupling process. A class of P-chiral, ferrocenyl phosphines was designed, synthesized, and evaluated for efficacy. Ultimately, these phosphines were found to be the most effective chiral ligands for coupling reactions of this class of alkynes, providing (E)-allylic alcohols in up to 67% ee and 85:15 regioselectivity. ... II. Total Syntheses of Amphidinolides T and T4 via Catalytic, Stereoselective Reductive Macrocyclizations Total syntheses of amphidinolides T and T4 were achieved using two nickelcatalyzed reductive coupling reactions of alkynes, with an epoxide in one case (intermolecular) and with an aldehyde in another (intramolecular). The latter was used to effect a macrocyclization, form a C-C bond and install a stereogenic center with >10:1 selectivity in both natural product syntheses. Alternative approaches in which intermolecular alkyne-aldehyde reductive coupling reactions would serve to join key fragments were investigated and are also discussed; it was found that macrocyclization was superior in several respects (diastereoselectivity, yield, and length of syntheses). Alkyneepoxide couplings were instrumental in the construction of key fragments corresponding to approximately half of the molecule of both natural products. In one case (T4 series), the alkyne-epoxide coupling exhibited very high site selectivity in a coupling of a diyne.
(cont.) A model for the stereoselectivity observed in the macrocyclizations is also proposed. ... amphidinolide T1 amphidinolide T4 * site of catalytic, stereoselective macrocyclization
by Elizabeth A. Colby Davie.
Ph.D.
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Casitas, Montero Alícia. « Reactivity of well-defined organometallic copper(III) complexes in carbon-heteroatom bond forming reactions ». Doctoral thesis, Universitat de Girona, 2012. http://hdl.handle.net/10803/81985.
Texte intégralRésumé :
This thesis is focused on the unexplored field of organometallic copper(III) chemistry. Arylcopper(III) complexes have been proposed as key intermediates in Ullmann condensation reactions that consist in the coupling of aryl halides and heteroatom nucleophiles catalyzed by copper. The study of the reactivity of well-defined arylcopper(III) complexes may provide a better understanding of the mechanism of Ullmann condensation reactions, which is still under intense debate. In this doctoral dissertation we study the feasibility of well-defined arylcopper(III) complexes, which are stabilized within macrocyclic ligands, to participate in C-heteroatom bond forming reactions. We develop copper-catalyzed C-N and C-O bond forming reactions, as well halide exchange reactions, including fluorinations, based on Cu(I)/Cu(III) catalytic cycle within model aryl halide substrates. We uncover the fundamental understanding of the two-electron redox steps, oxidative addition and reductive elimination, at copper.Aquesta tesi es centra en el camp de la química organometàl•lica del coure(III) que roman sense explorar. Els complexos arilcoure(III) s'han proposat com a intermedis clau en les reaccions de condensació Ullmann que consisteixen en l'acoblament d'halurs d'arils i nucleòfils basats en heteroàtoms catalitzades amb coure. L'estudi de la reactivitat de complexos arilcoure(III) ben definits pot proporcionar una millor comprensió del mecanisme de les reaccions de condensació Ullmann, el qual es troba sota un intens debat. En aquesta tesi doctoral s'estudia la viabilitat del complexos arilcoure(III), estabilitzats en lligands macrocíclics, de participar en reaccions de formació d'enllaç carboni-heteroàtom. S'han desenvolupat reaccions de formació d'enllaç C-N i C-O així com reaccions d'intercanvi d'halurs, on s'inclouen fluoracions, catalitzades amb coure i basades en un cicle catalític Cu(I)/Cu(III) utilitzant substrats models d'halur d'aril. S'ha obtingut una comprensió fonamental de les etapes redox a dos electrons, addició oxidant i eliminació reductiva, en coure.
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Trenkle, James D. (James Douglas). « Phosphine-promoted cross-coupling reactions of propargylcopper reagents and alkenyl iodides and the total synthesis of (-)-gloeosporone via nickel-catalyzed epoxide-alkyne reductive macrocyclization ». Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/39582.
Texte intégralRésumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2007.Vita.
Includes bibliographical references.
I. Phosphine-Promoted Cross-Coupling Reactions of Propargylcopper Alkenyl Iodides Reagents and Alkenyl Iodides. An electron-rich phosphine additive is critical and sufficient for propargyl-selective couplings of propargylcopper reagents and alkenyl iodides. This method is complementary to those previously described, in which high allenyl selectivity is observed in analogous coupling reactions. While the basis of the phosphine effect requires further investigation, the information gained in these studies enables the synthesis of complex molecules by way of skipped enyne intermediates. ... II. Total Synthesis of (-)-Gloeosporone via Nickel-Catalyzed Epoxide-Alkyne Reductive Macrocyclization. The total synthesis of macrolide natural product (-)-gloeosporone 1 is described in 10 steps (LLS) and 5.2% overall yield. The key macrocyclization was performed via nickel-catalyzed reductive macrocyclization of an alkyne and a epoxide to give the 14-membered ring in 46% yield (4a ---> 3a; up to 67% yield could be achieved with stoichiometric nickel). This transformation differs from previous strategies in closing the macrocycle of 1 using more traditional approaches such as macrolactonization and ring-closing metathesis. ...
(cont.) Additional nickel-catalyzed macrocyclization studies of alkynes and epoxides were undertaken with other alkynylepoxides. With these studies we were able to recognize an important structural pattern (a 6,e-unsaturated ynoate) which might be necessary for efficient cyclization. Using this information, the nickel-catalyzed reductive cyclization of alkynes and epoxides was extended to the formation of 12- and 15-membered rings.
by James D. Trenkle.
Ph.D.
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Duff, Jack Lawrence. « Single electron transfer in nucleophilic reactions of substituted norbornanes ». Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/27444.
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Holder, Grant Newton. « Redox reactivity of mononuclear and binuclear rhenium complexes ». Diss., Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/30392.
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羅政藩 et Chang-fan Lo. « Substitution and redox reactions of some binuclear platinum (II) and platinum (III) complexes ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1989. http://hub.hku.hk/bib/B31231901.
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Lo, Chang-fan. « Substitution and redox reactions of some binuclear platinum (II) and platinum (III) complexes / ». [Hong Kong : University of Hong Kong], 1989. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12505304.
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Kour, Gurpreet. « First principles investigations on transition metal based electrocatalysts for efficient clean energy conversion ». Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/232798/1/Gurpreet_Kour_Thesis.pdf.
Texte intégralRésumé :
This dissertation relates to the application of density functional theory to the design of novel nanoelectrocatalysts for various electrochemical reduction reactions such as carbon dioxide reduction reactions, carbon monoxide reduction reactions and nitrogen reduction reactions. Many electrocatalysts with high activity, excellent selectivity and stability were designed and engineered using first principle calculations. These findings could potentially guide the experimentalists for creating clean and sustainable energy resources.
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Moritz, Paul Stuart. « Substitution and redox chemistry of ruthenium complexes / ». Title page, contents and summary only, 1987. http://web4.library.adelaide.edu.au/theses/09PH/09phm862.pdf.
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Saleh, Nail Asad. « Dynamical solvent effect in 1-(9-anthryl)-3-(4-dimethylaniline) propane charge transfer reactions / ». free to MU campus, to others for purchase, 2002. http://wwwlib.umi.com/cr/mo/fullcit?p3060138.
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Dehestani, Ahmad. « Exploring reactivities of oxo and nitrido ligands on high valent osmium with electrophiles, nucleophiles, alkenes, hydrogen, and methane. / ». Thesis, Connect to this title online ; UW restricted, 2004. http://hdl.handle.net/1773/8626.
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Hyman, Matthew P. « A theoretical study of the electrocatalytic oxygen reduction reaction and related reactions on platinum group metals ». Connect to online resource, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3273680.
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Yan, Xuecheng. « Carbon-based Porous Materials for Electrochemical Reactions ». Thesis, Griffith University, 2016. http://hdl.handle.net/10072/366852.
Texte intégralRésumé :
The exploration of highly active and durable cathodic oxygen reduction reaction (ORR) catalysts with economical production cost is still the bottleneck to realize the large-scale commercialization of some emerging technologies, such as fuel cells and metal-air batteries. At present, the composite that contains expensive platinum (Pt) particles dispersed on a porous carbon support (e.g., activated carbon (AC)) is the most efficient ORR catalyst. In a common sense, the AC itself normally shows very low activity for the ORR, so the Pt particles are vital. Imagine that if we remove all of the Pt particles, can the remaining AC still play the similar role? The current work aims to make the inert AC active for the electrochemical reactions by creating unique defects in the AC.
First of all, different porous carbon materials with variable specific surface areas were synthesized by an easy and scalable chemical activation method. It is shown that all the activated samples demonstrate obviously improved ORR activity. Afterwards, the unique defects were introduced into the activated ACs via a facile nitrogen doping and removal approach to further enhance their catalytic performance, based on the defective mechanism that was proposed in our group, in which the nitrogen was incorporated into the ACs under an ammonia atmosphere at 500 °C and subsequently removed at 1050 °C under a nitrogen environment. The results showed that the doped nitrogen did not enhance the ORR performance of the synthesized samples directly, but the produced defects possibly served as the active sites for the ORR, which finally contributed to the catalytic performance improvement. Particularly, the resulting defective carbon (D-AC) derived from the highest surface area AC (3508 m2/g) also exhibits the best ORR performance in alkaline medium with low overpotential. For example, the ORR activity of the D-AC is comparable to the commercial Pt/C (20 wt% Pt) in terms of 4-electron pathway, half-wave potential and limiting current density, namely, 3.6, 0.771 V and 4.4 mA·cm-2 vs 3.9, 0.785 V and 5.0 mA·cm-2, respectively. Meanwhile, the D-AC also exhibits excellent HER activity, which is better than most of the reported metal-free HER catalysts, but with much lower production cost.School of Natural Sciences
Science, Environment, Engineering and Technology
Full Text
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Krasik, Pavel. « Asymmetric ruthenium catalyzed reduction reactions ». Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/6562.
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Sykes, Bridget Maree. « Reductively triggered internal cyclisation reactions ». Thesis, University of Auckland, 1994. http://hdl.handle.net/2292/1977.
Texte intégralRésumé :
Reductively triggered internal cyclisation reactions have been investigated as a prodrug system for the hypoxia selective release of aromatic nitrogen mustards. The observed pseudo-first-order rate coefficients of cyclisation of several model 2-aminoaryl-acetamides and propanamides have been measured. Cyclisation was observed to be strongly influenced by stereochemistry, whereas electron withdrawal from the amine-bearing ring resulted in a comparatively modest slowing of the rate of cyclisation. Protonation of the leaving group appeared to increase the rate of cyclisation, while changes in 4-substitution on the leaving amine had little effect on this rate. The cyclisation of 2-(2-aminophenyl) alkanamides was found to be subject to general catalysis by acidic buffer components, and rate determining formation of the tetrahedral intermediate has been proposed. Ring closure reactions of several 2-hydroxylaminophenylalkanamides have been studied by γ-radiolysis. HPLC methods have been developed for the separation of reduction and cyclisation products. Reduction stoichiometry implicates the hydroxylamine as the predominant reduction product of radiolysis of the 2-nitrophenylalkanamide precursors, which varied in the nature of substitution of the nitrobenzyl ring, 4-substitution of the leaving aniline, and overall geometry. Cyclisation via the hydroxylamino was observed to be significantly faster than that of its amino counterparts, and was similarly influenced by changes in geometry. The hydroxylamine undergoes a base catalysed, oxygen dependent reaction under aerobic conditions. This reaction did not appear to be influenced by the geometry of the compound. Substitution of the hydroxylamine-bearing ring with a carboxamide group (CONHR σp = 0.36) lowered the pH at which hydroxylamino-amide cyclisation was slowest, compared with its unsubstituted counterpart. The reaction was found to be aided by electron-withdrawal from the leaving amine. Rate determining breakdown of the tetrahedral intermediate has been proposed. Preliminary investigations have been made on 2-nitrophenyl alkyl esters and a 2,6-dinitrophenylamide prodrug system. Rapid, reductively triggered release of coupled phenols and amines has been observed from the nitro-esters and -amides, respectively. In contrast to amino-amide and hydroxylamino-amide cyclisation, gem-dimethyl substitution did not facilitate reductive release from the nitro-ester. The inability to measure the rates of reductive release in radiolysis solutions suggests that these reactions occur significantly faster than hydroxylamino-amide ring closure. Molecular mechanics calculations have been undertaken to investigate relationships between the geometry of 2-aminoarylalkanamides, and rates of cyclisation. The distance between, and angle of approach of the nucleophilic and electrophilic centres in the calculated minimum-energy conformer did not display a correlation with cyclisation rates.Whole document restricted, but available by request, use the feedback form to request access.
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Smith, Graeme Sinclair. « Electrochemically induced addition reactions ». Thesis, University of Edinburgh, 1987. http://hdl.handle.net/1842/11407.
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Barber, Drew. « Selenium In Thioredoxin Reductase : Resistance To Oxidative Inactivation, Oxidation States, And Reversibility Of Chemical Reactions ». ScholarWorks @ UVM, 2018. https://scholarworks.uvm.edu/graddis/943.
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Selenium is a required trace element which was originally discovered by the Swedish chemist Jons Jacob Berzelius in 1817. It was initially believed to be a toxin as it was identified as being the cause of hoof maladies and excessive hair loss in horses that feed upon plants with high selenium content. It wasn’t until 1957 that the potential contributions of selenium to physiology were first demonstrated. Selenium is now known to play a critical role in the maintenance of human health. Interestingly, unlike other trace metals/semi-metals, selenium is directly incorporated into proteins in the form of the amino acid selenocysteine (Sec) in a very complicated and energetically costly fashion. Though rare, being found in only 25 human proteins, Sec proteins are involved in numerous vital biological processes including maintenance of redox homeostasis and anti-oxidant defense. Even though Sec is essential, the reason that Sec replaces its structural analog cysteine (Cys) in only 25 proteins is not widely agreed upon. A previous model suggests that the replacement of Cys with Sec provides enzymes with a type of catalytic advantage. The presence of Cys-containing orthologs of mammalian Sec-enzymes in other eukaryotes argues against this model. A newer model to explain the use of Sec is that the gain of function imparted to an enzyme by replacing Cys with Sec is the ability of Sec to impart chemical reversibility.
Building on previous results from our lab demonstrating the ability of Sec to confer proteins with the ability to resist over oxidation we have elucidated the mechanism by which Sec containing thioredoxin reductase (TrxR) resists over oxidation. The ability of Sec-TrxR to resist oxidative inactivation is due to the greater electrophilicity of Sec relative to Cys. This allows for quicker resolution and prevents over oxidation. Based on these findings we also investigate the utility of the alkylating agent dimedone to probe the oxidation state of Sec. Interestingly, it was discovered that dimedone will react with seleneninic acid with the resulting adduct being labile. Additonally it was discovered that dimedone will also react with seleninic acid, resulting in the formation of a dimedone dimer. These results call into question the usefulness of dimedone in deteremining the oxidation state of Sec. Finally, we provide evidence that Sec-TrxR enzymes are able to catalyze single electron reductions. This is most likely due to the formation of a stable Sec radical intermediate. As a whole this project provides support for the theory that Sec was selected for due to its ability to convey chemical reversiablity to proteins.
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McEvoy, J. « Two-stage catalysis of reduction reactions ». Thesis, University of Liverpool, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233867.
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Kwasny, Richard S. « Hazard assessment strategies for reduction reactions ». Thesis, London South Bank University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298377.
Texte intégralRésumé :
Reduction reactions involving heterogeneous catalytic hydrogenations, complex metal hydrides, and to lesser degree hydrogen-transfer reactions, are regularly scaled-up in pilot plants. Unfortunately, thermal runaway incidents involving reduction reactions do occur, despite best efforts to prevent them through the application of a chemical reaction hazard assessment strategy. A review of the literature, plant incidents, thermochemical and calorimetric techniques, identified the requirements for a unique assessment strategy for reduction reactions. The preference was to safeguard the plant using preventive measures first which were supported by adequate protective measures. The basis of safety was defined by, the boiling point of the reaction mass, the process temperature and the adiabatic temperature rise for the desired and/or adverse reactions including other kinetic data, e. g., "time to maximum rate". A number of instrumental and thermochemical procedures were adopted for the hazard identification portion of the strategy. The DSC capillary and ampoule techniques were used for substrate thermal decomposition and air oxidation determinations including reaction solution thermal stability studies. An estimation technique (Yoshida) used DSC exothermic data to predict a substrate's susceptibility of being shock sensitive and/or explosion propagating. An evolved gas mass flow detector was coupled to a reaction calorimeter to determine the maximum off-gas rate. A modified stirred ARC for hydrogenations and a stirred-micro-calorimeter for the quantification of the adverse reaction were developed. Adiabatic determinations for quantification of the adverse reaction were variable. The heat losses were unacceptable for a controlled hydrogenation in a modified stirred ARC. Results for the stirred-micro-calorimeter were satisfactory. However, adverse reactions for hydride decompositions and "shot additions" yielded adequate calorimetric results. A series of controlled experiments by reaction calorimeter coupled with an insitu FTIR, characterised the thermochemistry, reaction kinetics, mass transfer coefficient and reaction mechanism for the desired and inhibited hydrogenations. A customised What-If? /Checklist process hazard analysis technique was developed for reduction reactions and two worked examples are presented. A hazard assessment strategy with appropriate hazard identification procedures was developed. Eight case studies (three hydrogenations, three hydride reductions and two hydrogen-transfer reactions) were used as examples to validate the reduction assessment strategy and hazard identification procedures.
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Jenson, David L. Jenson. « Proton-coupled electron transfer and tyrosine D of phototsystem II ». Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/29667.
Texte intégralRésumé :
Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2010.Committee Chair: Bridgette Barry; Committee Member: Ingeborg Schmidt-Krey; Committee Member: Jake Soper; Committee Member: Nils Kroger; Committee Member: Wendy Kelly. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Oswald, Claire Louise. « Enantioselective copper-catalysed reductive Michael cyclisations ». Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/4614.
Texte intégralRésumé :
Hydrometalation of α,β-unsaturated carbonyl compounds provides access to reactive metal enolates, which can then be trapped by a suitable electrophile. The coppercatalysed reductive aldol reaction involves hydrometalation of an α,β-unsaturated carbonyl compound, followed by an inter- or intramolecular aldol reaction. While there have been numerous examples of copper-catalysed reductive aldol reactions reported in the literature, the corresponding reductive Michael reaction has been relatively understudied. Herein, the copper-catalysed reductive Michael cyclisation of substrates containing two α,β-unsaturated carbonyl moieties is described. A range of structurally and electronically diverse substrates were prepared by various different methods. Both α,β-unsaturated ketones and esters underwent cyclisation, in the presence of a copper catalyst, a bisphosphine ligand, and a stoichiometric reductant, to afford 5- and 6- membered carbocyclic and heterocyclic products, with good-to-excellent levels of diastereo- and enantiocontrol. Furthermore, the diastereochemical outcome of these reactions is dependent on the specific reaction conditions used.
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Choi, Eun-Young. « Studies on the reaction mechanism of the reductive half-reaction of Xanthine Oxidase / ». The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu148819366523445.
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Lippert, Cameron A. « Redox-active ligand-mediated radical coupling reactions at high-valent oxorhenium complexes : reactions relevant to water oxidation for artificial photosynthesis ». Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41199.
Texte intégralRésumé :
The making and breaking of O-O bonds has implications ranging from artificial photosynthesis and water oxidation to the use of O₂ as a selective, green oxidant for transformations of small molecules. Oxidative generation of O₂ from coupling of two H₂O molecules remains challenging, and well defined systems that catalytically evolve O₂ are exceedingly rare. Recent theoretical studies have invoked metal oxyl radicals (L[subscript n]M=O*) containing a singly occupied M-O π-type orbital as precursors to O-O bond forming events in both biological and synthetic water oxidation catalysts. However, the lack of stable metal oxyl complexes makes it difficult to explore and understand this hypothesis. The activation of dioxygen (breaking of O-O bonds) to produce terminal metal oxos also remains a challenge. There is an inherent kinetic barrier to the spin-forbidden reactions of triplet dioxygen, and features that engender selective O₂ reduction are not easily transferable from system to system. The primary thrust of this thesis work has been to elaborate new methods to generate well-defined metal oxyl radicals for studies of their reactions in radical bond-forming reactions similar to the radical coupling hypothesis of water oxidation.
A library of >20 5- and 6-coordinate high-valent oxorhenium complexes containing redox-inert and redox-active ligands has been prepared. The complexes containing redox-active ligands have shown the ability for ligand-mediated radical coupling reactions. Mechanistic studies of bimetallic O₂ homolysis (the microscopic reverse of water oxidation) and nitroxyl radical deoxygenation at five-coordinate oxorhenium(V) reveal that, in both net 2e⁻ reactions, coupling to a redox-active ligand lowers the kinetic barrier to the reaction by facilitating formation and stabilization of 1e⁻ oxidized intermediates.
Coordinatively unsaturated high-valent oxorhenium complexes containing redox-active ligands direct bond-forming reactions towards the metal center. This is undesirable towards the goal of forming O-O bonds. To address this problem coordinatively saturated Re(V) and Re(VII) complexes were prepared. Oxidation of these species by chemical oxidants allowed for the isolation of "masked" oxyl species. These complexes showed reactivity towards Si and trityl radicals to produce new Si-O and C-O bonds, whereas their closed-shell congeners were inert. We have successfully developed a method for the preparation and isolation of "masked" oxyl radicals and shown their utility in ligand-mediated radical coupling reactions.