Tesis sobre el tema "Homogenous catalysts"
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1
Ruiz, Botella Sheila. "The importance of ligand design for the development of supramolecular catalysts and ion receptors". Doctoral thesis, Universitat Jaume I, 2017. http://hdl.handle.net/10803/402550.
Resumen
La tesis está dividida en dos partes claramente diferenciadas. La primera parte trata sobre aspectos concernientes a la catálisis supramolecular. Los trabajos descritos están basados en el diseño de nuevos ligandos N-heterociclicos con diferentes topologías y funcionalidades, los cuales fueron coordinados a diferentes centros metálicos. Los complejos sintetizados fueron caracterizados y estudiados en catálisis, con el objetivo principal de estudiar los efectos producidos por los ligandos orgánicos debido a interacciones del tipo no covalentes. Estos complejos o catalizadores también fueron soportados y estudiados en catálisis heterogénea.
La segunda parte de la tesis se centra en estudios de química supramolecular host-guest. Los trabajos descritos en esta parte describen la preparación de nuevos receptores ionicos basados en esqueletos de resorcinareno cavitando y/o esqueletos de naturaleza tripodal. Se estudiaron y analizadores los diferentes modos de interacción y las constantes de asociación hacia una gran variedad de guests de diferente naturaleza.The present thesis is divided in two different parts. Part 1 is titled the importance of ligand design for the development of supramolecular catalysts. This part includes three different chapters: introduction chapter 1, chapter 2 and chapter 3. Chapter 1 shows a brief overview of the most interesting items related to supramolecular catalysis. In chapter 2 is described the synthesis and characterization of three different p-xylylbis-benzimidazolylidene iridium and rhodium complexes. Chapter 3 reports the synthesis, characterization and catalytic studies of different palladium, iridium and rhodium complexes, which are formed by N-heterocyclic ligands featuring different topologies, and some of them decorated with pyrene functionalities. The importance and influence of these ligands in the conformational and catalytic behaviour of the metal complexes is studied in detail, providing evidences of the effects produces due to non-covalent interactions such as π-π interactions. Part 2 is titled the importance of ligand design for the development of ion receptors. This part includes three chapters: introduction chapter 4, chapter 5 and chapter 6. Chapter 4 is a brief introduction of the most relevant aspects related to supramolecular host-guest chemistry. The approaches described in chapter 5 consist of two different strategies for the preparation of imidazole resorcinarene based cavitands for the recognition of anions or cations. Chapter 6 reports the synthesis of tris-azolium and tris-iodoazolium tripodal receptors for the recognition of anions. In both chapters (5 and 6) are studied the binding capabilities of the receptors towards several ions, showing the importance of the development in ligand design to improve the properties of the receptors.
2
Guo, Chris. "Alkane Oxidation Catalysis by Homogeneous and Heterogeneous Catalyst". Thesis, The University of Sydney, 2005. http://hdl.handle.net/2123/622.
Resumen
Abstract Cobalt-based complexes are widely used in industry and organic synthesis as catalysts for the oxidation of hydrocarbons. The Co/Mn/Br (known as "CAB system") catalyst system is effective for the oxidation of toluene. The Co/Mn/Br/Zr catalyst system is powerful for the oxidation of p-xylene, but not for the oxidation of toluene. [Co3O(OAc)5(OH)(py)3][PF6] (Co 3+ trimer 5) is more effective than [Co3O(OAc)6(py)3][PF6] (Co 3+ trimer 6) as a catalyst in the CAB catalyst system. Higher temperatures favour the oxidation of toluene. Zr 4+ does not enhance the oxidation of toluene. Zr 4+ could inhibit the oxidation of toluene in the combination of Co/Br/Zr, Co/Mn/Zr or Co/Zr. NHPI enhances the formation of benzyl alcohol, but the formation of other by-products is a problem for industrial processes. Complex(es) between cobalt, manganese and zirconium might be formed during the catalytic reaction. However, attempts at the preparation of complexes consisting of Co/Zr or Mn/Zr or Co3ZrP or Co8Zr4 clusters failed. The oxidation of cyclohexane to cyclohexanone and cyclohexanol is of great industrial significance. For the homogeneous catalysis at 50 o C and 3 bar N2 pressure, the activity order is: Mn(OAc)3 �2H2O > Mn12O12 cluster > Co 3+ trimer 6 > [Co3O(OAc)3(OH)2(py)5][PF6]2 (Co 3+ trimer 3) > Co 3+ trimer 5 > Co(OAc)2 �4H2O > [Co2(OAc)3(OH)2(py)4][PF6]-asym (Co dimerasym) > [Co2(OAc)3(OH)2(py)4][PF6]-sym (Co dimersym); whereas [Mn2CoO(OAc)6(py)3]�HOAc (Mn2Co complex) and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. But at 120 o C and 3 bar N2 pressure, the activity order is changed to: Co dimerasym > Co(OAc)2 �4H2O > Co trimer 3 and Mn(OAc)3 �2H2O > Co 3+ trimer 6 > Mn2Co complex > Co 3+ trimer 5 > Co dimersym > Mn12O12 cluster. The molar ratio of the products was close to cyclohexanol/cyclohexanone=2/1. Mn(II) acetate and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. Among those cobalt dimers and trimers, only the cobalt dimerasym survived after the stability tests, this means that [Co2(OAc)3(OH)2(py)4][PF6]-asym might be the active form for cobalt(II) acetate in the CAB system. Metal-substituted (silico)aluminophosphate-5 molecular sieves (MeAPO-5 and MeSAPO-5) are important heterogeneous catalysts for the oxidation of cyclohexane. The preparation of MeAPO-5 and MeSAPO-5 and their catalytic activities were studied. Pure MeAPO-5 and MeSAPO-5 are obtained and characterised. Four new pairs of bimetal-substituted MeAPO-5 and MeSAPO-5(CoZr, MnZr, CrZr and MnCo) were prepared successfully. Two novel trimetal-subtituted MeAPO-5 and MeSAPO-5 (MnCoZr) are reported here. Improved methods for the preparation of four monometal-substituted MeAPO-5 (Cr, Co, Mn and Zr) and for CoCe(S)APO-5 and CrCe(S)APO-5 are reported. Novel combinational mixing conditions for the formation of gel mixtures for Me(S)APO-5 syntheses have been developed. For the oxidation of cyclohexane by TBHP catalysed by MeAPO-5 and MeSAPO-5 materials, CrZrSAPO-5 is the only active MeSAPO-5 catalyst among those materials tested under conditions of refluxing in cyclohexane. Of the MeAPO-5 materials tested, whereas CrCeSAPO-5 has very little activity, CrZrAPO-5 and CrCeAPO-5 are very active catalysts under conditions of refluxing in cyclohexane. MnCoAPO-5, MnZrAPO-5 and CrAPO-5 are also active. When Cr is in the catalyst system, the product distribution is always cyclohexanone/cyclohexanol equals 2-3)/1, compared with 1/2 for other catalysts. For MeAPO-5, the activity at 150 o C and 10 bar N2 pressure is: CrZrAPO-5 > CrCeAPO-5 > CoZrAPO-5. For MeAPO-5 and MeSAPO-5, at 150 o C and 13 bar N2 pressure, the selectivity towards cyclohexanone is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5; and the selectivity towards cyclohexanol is: MnZrAPO-5 > CrZrAPO-5 > MnCoAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5. Overall the selectivity towards the oxidation of cyclohexane is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5. The amount of water in the system can affect the performance of CrCeAPO-5, but has almost no effect on CrZrAPO-5. Metal leaching is another concern in potential industrial applications of MeAPO-5 and MeSAPO-5 catalysts. The heterogeneous catalysts prepared in the present work showed very little metal leaching. This feature, coupled with the good selectivities and effectivities, makes them potentially very useful.
3
Guo, Chris. "Alkane Oxidation Catalysis by Homogeneous and Heterogeneous Catalyst". University of Sydney. Chemistry, 2005. http://hdl.handle.net/2123/622.
Resumen
Abstract Cobalt-based complexes are widely used in industry and organic synthesis as catalysts for the oxidation of hydrocarbons. The Co/Mn/Br (known as "CAB system") catalyst system is effective for the oxidation of toluene. The Co/Mn/Br/Zr catalyst system is powerful for the oxidation of p-xylene, but not for the oxidation of toluene. [Co3O(OAc)5(OH)(py)3][PF6] (Co 3+ trimer 5) is more effective than [Co3O(OAc)6(py)3][PF6] (Co 3+ trimer 6) as a catalyst in the CAB catalyst system. Higher temperatures favour the oxidation of toluene. Zr 4+ does not enhance the oxidation of toluene. Zr 4+ could inhibit the oxidation of toluene in the combination of Co/Br/Zr, Co/Mn/Zr or Co/Zr. NHPI enhances the formation of benzyl alcohol, but the formation of other by-products is a problem for industrial processes. Complex(es) between cobalt, manganese and zirconium might be formed during the catalytic reaction. However, attempts at the preparation of complexes consisting of Co/Zr or Mn/Zr or Co3ZrP or Co8Zr4 clusters failed. The oxidation of cyclohexane to cyclohexanone and cyclohexanol is of great industrial significance. For the homogeneous catalysis at 50 o C and 3 bar N2 pressure, the activity order is: Mn(OAc)3 �2H2O > Mn12O12 cluster > Co 3+ trimer 6 > [Co3O(OAc)3(OH)2(py)5][PF6]2 (Co 3+ trimer 3) > Co 3+ trimer 5 > Co(OAc)2 �4H2O > [Co2(OAc)3(OH)2(py)4][PF6]-asym (Co dimerasym) > [Co2(OAc)3(OH)2(py)4][PF6]-sym (Co dimersym); whereas [Mn2CoO(OAc)6(py)3]�HOAc (Mn2Co complex) and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. But at 120 o C and 3 bar N2 pressure, the activity order is changed to: Co dimerasym > Co(OAc)2 �4H2O > Co trimer 3 and Mn(OAc)3 �2H2O > Co 3+ trimer 6 > Mn2Co complex > Co 3+ trimer 5 > Co dimersym > Mn12O12 cluster. The molar ratio of the products was close to cyclohexanol/cyclohexanone=2/1. Mn(II) acetate and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. Among those cobalt dimers and trimers, only the cobalt dimerasym survived after the stability tests, this means that [Co2(OAc)3(OH)2(py)4][PF6]-asym might be the active form for cobalt(II) acetate in the CAB system. Metal-substituted (silico)aluminophosphate-5 molecular sieves (MeAPO-5 and MeSAPO-5) are important heterogeneous catalysts for the oxidation of cyclohexane. The preparation of MeAPO-5 and MeSAPO-5 and their catalytic activities were studied. Pure MeAPO-5 and MeSAPO-5 are obtained and characterised. Four new pairs of bimetal-substituted MeAPO-5 and MeSAPO-5(CoZr, MnZr, CrZr and MnCo) were prepared successfully. Two novel trimetal-subtituted MeAPO-5 and MeSAPO-5 (MnCoZr) are reported here. Improved methods for the preparation of four monometal-substituted MeAPO-5 (Cr, Co, Mn and Zr) and for CoCe(S)APO-5 and CrCe(S)APO-5 are reported. Novel combinational mixing conditions for the formation of gel mixtures for Me(S)APO-5 syntheses have been developed. For the oxidation of cyclohexane by TBHP catalysed by MeAPO-5 and MeSAPO-5 materials, CrZrSAPO-5 is the only active MeSAPO-5 catalyst among those materials tested under conditions of refluxing in cyclohexane. Of the MeAPO-5 materials tested, whereas CrCeSAPO-5 has very little activity, CrZrAPO-5 and CrCeAPO-5 are very active catalysts under conditions of refluxing in cyclohexane. MnCoAPO-5, MnZrAPO-5 and CrAPO-5 are also active. When Cr is in the catalyst system, the product distribution is always cyclohexanone/cyclohexanol equals 2-3)/1, compared with 1/2 for other catalysts. For MeAPO-5, the activity at 150 o C and 10 bar N2 pressure is: CrZrAPO-5 > CrCeAPO-5 > CoZrAPO-5. For MeAPO-5 and MeSAPO-5, at 150 o C and 13 bar N2 pressure, the selectivity towards cyclohexanone is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5; and the selectivity towards cyclohexanol is: MnZrAPO-5 > CrZrAPO-5 > MnCoAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5. Overall the selectivity towards the oxidation of cyclohexane is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5. The amount of water in the system can affect the performance of CrCeAPO-5, but has almost no effect on CrZrAPO-5. Metal leaching is another concern in potential industrial applications of MeAPO-5 and MeSAPO-5 catalysts. The heterogeneous catalysts prepared in the present work showed very little metal leaching. This feature, coupled with the good selectivities and effectivities, makes them potentially very useful.
4
Damian, Karen Serena. "Pd catalysed synthesis of phosphines for homogeneous catalysis". Thesis, St Andrews, 2009. http://hdl.handle.net/10023/907.
5
Craig, Kim Meyer. "New concepts in catalyst design: homogeneous organometallic catalysts with tunable architectures". Thesis, University of Auckland, 2010. http://hdl.handle.net/2292/6114.
Resumen
This theses describes the development of homogeneous catalysts containing receptor elements which are capable of participating in reversible bonding interactions with groups bearing complementary functionality. This approach is amenable to combinatorial chemistry, and could facilitate catalyst development processes which are conventionally expensive and time-intensive. To date, the implication of reversible supra molecular interactions in anthropogenic organometallic catalysis are not widely understood.
6
Gao, Tianyu. "Hétérogénéisation de catalyseurs homogènes à l'aide de matériaux à structures organiques covalentes". Electronic Thesis or Diss., Centrale Lille Institut, 2022. http://www.theses.fr/2022CLIL0016.
Resumen
L'hétérogénéisation des catalyseurs homogènes est un moyen efficace pour réaliser leur réutilisation. Les matériaux à structures organiques covalentes (Covalent Organic Frameworks ou COF en anglais) sont des matériaux poreux prometteurs qui méritent d'être développés en raison de leur surface spécifique importante, de leur structure microporeuse et de leur stabilité thermique élevée pour jouer le rôle de structure hôte pour l'hétérogénéisation de catalyseurs homogènes. Dans cette thèse, l'acide phosphotungstique homogène (HPW) est hétérogénéisé via son encapsulation dans l'espacement intercouche du COF 2D CIN-1. Le catalyseur hétérogénéisé HPW@CIN-1 montre des activités catalytiques intéressantes et une grande stabilité dans les réactions modèles testées. D’une manière similaire, l'hétérogénéisation d’un complexe organique de Ru est obtenue via son encapsulation dans l'espacement intercouche du COF CIN-1 fonctionnalisé. Le catalyseur hétérogène Ru@CIN-1 obtenu présente une activité catalytique et une stabilité élevée dans des réactions modèles d'amination et d'hydrogénation. Afin d'élargir l'application du catalyseur Ru@CIN-1, ce dernier a été pyrolysé sous atmosphère inerte. Le nouveau matériau Ru@g-C3N4 ainsi obtenu démontre une excellente performance en électrocatalyse de l’eau. Enfin, le catalyseur Fe(NO3)3 homogène est hétérogénéisé par greffage sur un COF 2D bidentate substitué par des groupements hydroxyles (LZU1-OH). Le catalyseur Fe@LZU1-OH obtenu présente une activité et une stabilité supérieures dans les réactions modèles d'oxydation testées par rapport au catalyseur homogène parentHeterogenization of homogeneous catalysts is an effective way to combine highactivity, selectivity and recyclability of catalysts. Covalent Organic Frameworks (COF) are promising organic porous materials that are worthy to be developed as host structures for the heterogenization of homogeneous catalysts, due to their high specific surface area, microporous structure, easy functionalization and high thermal stability. In this thesis, homogeneous phosphotungstic acid (HPW) is heterogenized via encapsulation into the interlayer spacing of 2D COF CIN-1. The heterogenized HPW@CIN-1 catalyst shows high catalytic activities and stability in acid-catalyzed reactions. Heterogenization of homogeneous Ru ions is achieved via tethering by diphenylphosphinobenzaldehyde ligand in the interlayer spacing of CIN-1. The obtained heterogenous Ru@CIN-1 catalyst shows high catalytic activity and stability in model reactions of amination and hydrogenation. In order to widen the application of Ru@CIN-1 catalyst, it has been pyrolyzed under inert atmosphere to obtain Ru supported over carbon nitride material. The obtained novel Ru@g-C3N4 material demonstrates a super performance in electrocatalytic water splitting. Homogeneous Fe(NO3)3 catalyst is heterogenized via grafting to hydroxyl-substituted bidentate 2D COF LZU1 (LZU1-OH). The obtained Fe@LZU1-OH catalyst shows high activity in oxidation model reactions comparable to the parent homogeneous catalyst at high stability
7
Richardson, John Michael. "Distinguishing between surface and solution catalysis for palladium catalyzed C-C coupling reactions: use of selective poisons". Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22704.
Resumen
This work focuses on understanding the heterogeneous/homogeneous nature of the catalytic species for a variety of immobilized metal precatalysts used for C-C coupling reactions. These precatalysts include: (i) tethered organometallic palladium pincer complexes, (ii) an encapsulated small molecule palladium complex in a polymer matrix, (iii) mercapto-modified mesoporous silica metalated with palladium acetate, and (iv) amino-functionalized mesoporous silicas metalated with Ni(II). As part of this investigation, the use of metal scavengers as selective poisons of homogeneous catalysis is introduced and investigated as a test for distinguishing heterogeneous from homogeneous catalysis. The premise of this test is that insoluble materials functionalized with metal binding sites can be used to selectively remove soluble metal, but will not interfere with catalysis from immobilized metal. In this way the test can definitely distinguish between surface and solution catalysis of immobilized metal precatalysts.
This work investigates three different C-C coupling reactions catalyzed by the immobilized metal precatalysts mentioned above. These reactions include the Heck, Suzuki, and Kumada reactions. In all cases it is found that catalysis is solely from leached metal. Three different metal scavenging materials are presented as selective poisons that can be used to determine solution vs. surface catalysis. These selective poisons include poly(vinylpyridine), QuadrapureTM TU, and thiol-functionalized mesoporous silica. The results are contrasted against the current understanding of this field of research and subtleties of tests for distinguishing homogeneous from heterogeneous catalysis are presented and discussed.
8
Schätz, Alexander. "Immobilization of homogeneous catalysts on nanoparticles and their application in semi-heterogeneous catalysis". kostenfrei, 2009. http://www.opus-bayern.de/uni-regensburg/volltexte/2009/1239/.
9
Martins, Tânia Isabel Quintas. "Continuous flow homogeneous catalysis using ionic liquid/supercritical fluid biphasic systems". Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/982.
Resumen
Ionic liquid/scCO₂ biphasic systems have been studied as a possible solution to the main problems concerning homogeneous catalysis reactions such as, the product/catalyst separation, the catalyst retention in the reaction medium and the use of organic solvents. The hydroformylation of long chain alkenes (1-octene) has been carried out as a continuous flow reaction using [OctMIM]Tf₂N (OctMIM = 1-octyl-3-methylimidazolium, Tf = CF₃SO₂) as the reaction solvent and scCO₂as the mobile phase to extract the products. The performance of the rhodium complexes formed with the ionic ligands [PentMIM][TPPTS] (1-pentyl-3- methylimidazolium tri(m-sulfonyl)triphenylphosphine) and [OctMIM][TPPTS] (1-octyl-3- methylimidazolium tri(m-sulfonyl)triphenylphosphine) is described under different sets of experimental conditions. Continuous flow hydroformylation of 1-octene was also carried out using a SILP (Supported Ionic Liquid Phase) catalyst formed with the TPPTS-based ionic ligands named above. The SILP system described in this work has the peculiarity of introducing the “without gases” approach: syn gas was synthesised in situ by the decomposition of formaldehyde. The performance of both systems is compared in the end. The extension of the continuous flow ionic liquid/scCO₂ biphasic system is shown with the optimisation of the silver-catalysed heterocyclisation of furans. A comparison is carried out with a previously developed and optimised continuous flow heterogeneous system.
10
Lummiss, Justin Alexander MacDonald. "Olefin Metathesis: Life, Death, and Sustainability". Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/32277.
Resumen
Over the past 15 years, ruthenium-catalyzed olefin metathesis has emerged as a cornerstone synthetic methodology in academia. Applications in fine-chemicals and pharmaceutical manufacturing, however, are just beginning to come on stream. Industrial uptake has been impeded by economic constraints associated with catalyst costs. These are due both to direct costs (exacerbated by intellectual property issues), and to further pressure exerted by the low turnover numbers attainable, and the need for extensive purification to remove ruthenium residues. From another perspective, however, these difficulties can be seen as arising from our rudimentary understanding of the fundamental organometallic chemistry of the Ru=CHR bond.
In particular, we know little about the nature and reaction pathways of the Ru-methylidene unit present in the active species that propagates metathesis, and in the catalyst resting state. We know slightly more about the ruthenacyclobutane species, but still too little to guide us as to their non-metathetical reaction pathways, their contribution to deactivation relative to the methylidene species, and potential work-arounds. This thesis work was aimed at improving our understanding of the reactivity, speciation, and decomposition of key ruthenium intermediates in olefin metathesis. A major focus was the behaviour and deactivation of species formed from the second-generation Grubbs catalyst RuCl2(H2IMes)(PCy3)(=CHPh) (S-GII), which dominates ring-closing metathesis. Also studied were derivatives of the corresponding IMes catalyst A-GIIm, containing an unsaturated Nheterocyclic
carbene (NHC) ligand. The methylidene complexes RuCl2(NHC)(PCy3)(=CH2) (GIIm) represent the resting state of
the catalyst during ring-closing and cross-metathesis reactions: that is, the majority Ru species
present during catalysis. Mechanistic studies of these key intermediates have been restricted,
however, by the low yields and purity with which they could be accessed. Initial work therefore
focused on designing a clean, high-yield route to the second-generation Grubbs methylidene
complexes S-GIIm and A-GIIm. These routes were subsequently expanded to develop access to
isotopically-labelled derivatives. Locating a 13C-label at the key alkylidene site, in particular,
offers a powerful means of tracking the fate of the methylidene moiety during catalyst
deactivation. Access to GIIm enabled detailed studies of the behaviour and decomposition of the Grubbs
catalysts. First, the long-standing question of the impact of saturation of the NHC backbone (i.e.
IMes vs. H2IMes) was examined. Dramatic differences in the behaviour of the two complexes
were traced to profound differences in PCy3 lability arising from the diminished π-acidity of the
IMes ligand. Secondly, the vulnerability of GIIm to nucleophiles was examined. This is an
important issue from the perspective of decomposition by adventitious nucleophiles in the
reaction medium during catalysis, but also reflects on substrate scope. For amine additives, the
dominant deactivation pathway was shown to typically involve attack on the resting-state
methylidene complex, not the metallacyclobutane, which has often been regarded as the most
vulnerable intermediate. In addition, the sigma-alkyl intermediate formed by nucleophilic attack
of displaced phosphine at the methylidene carbon was trapped by moving to the first-generation
complex, and using a nitrogen donor (pyridine) that cannot promote decomposition via N–H
activation pathways. Interception of this long-suspected species led to the proposal of “donorinduced”
deactivation as a general decomposition pathway for Grubbs-class catalysts.
Finally, the capacity of phosphine-free catalysts to overcome the shortcomings of the secondgeneration
Grubbs catalysts was demonstrated, in a case study involving application of crossmetathesis
(CM) to the synthesis of a high-value antioxidant. An efficient CM methodology was
developed for the reaction of renewable essential-oil phenylpropenoids with vinyl acrylates. This
work illustrates a new paradigm in sustainable metathesis. Rather than degrading unsaturated
feedstocks via metathesis (a process that can be termed “metathe[LY]sis”), it demonstrates how
metathesis with directly-functionalized olefins can be used to augment structure and function.
From the perspective of organometallic chemistry and catalyst design, key comparisons built
into this thesis are the effect of the NHC ligand (IMes vs. H2IMes) and its trans ancillary ligand
on the efficient entry into catalysis; the susceptibility to nucleophilic attack of the alkylidene
ligand (benzylidene vs. methylidene) vs. the metallacyclobutane; and the effect of replacing a
phosphine ancillary ligand with a non-nucleophilic donor.
From a practical standpoint, Chapter 2 brings new life to metathesis with the high-yield
synthesis of the resting state species, Chapters 3 and 4 examine the deactivation, or death, of the
methylidene complexes, and Chapter 5 establishes a new paradigm for olefin metathesis within
the context of sustainable synthesis.
11
Craythorne, Steven James. "Heterogenizing homogeneous hydrogenation catalysts". Thesis, Queen's University Belfast, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486059.
Resumen
Catalysts frequently used in the fine chemical industries are qften homogeneous, therefore requiring expensive and time consuming methods of catalyst regeneration. The loss of expensive transition metals used in most homogeneous catalysts is significant, and further tests must be conducted to measure levels of contamination of the final product, a critical consideration in the phannaceutical and foodstuffs industries. This thesis reports the synthesis, material preparation and testing of three methods of entrapping active catalysts. The methods described have been developed to fulfill the conditions suitable for the individual catalyst. Acidic, basic and fast gelling sol-gel techniques are discussed in which silica based glasses, ionogels and organogels are functionalized with active catalyst species. These cat~lysts have undergone the hydrogenation of styrene, the enantioselective hydrogenation of geraniol and the transfer hydrogenation ofacetophenone. We report the results of catalytic reactions employing these heterogenized homogenous catalysts comparable in selectivity and conversion to their homogeneous counterparts, yet having ease of separation. and effortless handling conditions equivalent to and (in some cases) better than corresponding heterogeneous catalysts. We also report the negligible metal leaching in our catalyst systems.
12
Jones, Rebecca S. "Carbon Dioxide as a Benign Solvent for Homogeneous Catalyst Recovery and Recycle". Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/11641.
Resumen
We have successfully investigated the use of CO2 as a miscibility switch to create an environment in which we can run a homogeneously catalyzed reaction while maintaining a heterogeneous separation. We explored the use of this technique with fluorous biphasic systems, a fluorous solid support, and aqueous biphasic systems.
In the case of the fluorous systems, CO2 was added to induce solubility of the fluorous catalyst. When the reaction was completed, CO2 was vented and the system returned to a biphasic state, making the separation easy.
For the aqueous biphasic systems, the organic phase is chosen such that it is fully miscible with water at ambient conditions. Examples include acetonitrile, THF, and dioxane. The addition of CO2 reduces the polarity of the solvent and causes a phase split. The recovery of the water-soluble catalyst is once again heterogeneous.
The application to aqueous biphasic systems is the most exciting studied. Aqueous biphasic systems are used industrially in the hydroformylation of propylene. With our technique, these systems can be extended to more hydrophobic substrates. We have shown a rate increase of 65 fold and 99% product recovery at modest pressures for the hydroformylation of 1-octene.
These aqueous biphasic systems also show much promise in the arena of enzyme catalyzed reactions. We can create an environment in which the enzyme kinetics will no longer be mass transfer limited.
13
Müller, Ruben S. Ramon. "Homogeneous gold catalysts : development of applications for gold(I) catalysts bearing N-heterocyclic carbene ligands". Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/2531.
Resumen
Recently established as an excellent activator for π-systems, efforts made in gold chemistry have increased enormously, resulting in a new ‘Gold Rush’ in chemistry. This thesis is a small contribution to it. There are two main aspects dominating the following chapters: gold catalysts bearing N-heterocyclic carbenes (NHCs) as supporting ligand, and H₂O assisted catalysis. The initial motivation for the presented work was to specifically demonstrate the potential of [(NHC)AuCl] as suitable catalysts for both known and new organic transformations and to establish these commercially available catalysts in gold chemistry, a field currently dominated by phosphine bearing gold complexes. Water mediated catalysis became the next repeatingly occurring aspect of this thesis by pursuing this initial aim and finding water as a useful solvent or agent, respectively. Various useful applications for gold-NHC complexes are presented, starting with the Meyer-Schuster rearrangement of propargylic alcohols as a continuation of the work realized with propargylic acetates by the Nolan group in early investigations on gold catalysts. Next, a study on alkyne hydration is presented with focus on low catalysts loadings to establish gold catalysts as a powerful choice for such a highly relevant reaction. The catalytic system is then advantageously adapted to a silver-free variation, still active at low catalyst loadings and with further mechanistic insight. Inspired by gold activation of alkynes, a gap of reactivity in gold catalysis is closed by a successful demonstration of nitrile hydration, a functionality previously thought to be inert towards gold activation. In this context, formation and role of dinuclear hydroxy-bridged gold complexes is investigated highlighting these complexes as a possible resting state of gold complexes in the presence of water. Next, the formation of furanones via alkoxylation/lactonization of propargylic propiolates is presented, an observation initially made when exploring the scope of the Meyer-Schuster rearrangement. The dissertation finally closes with the gold-catalyzed formation of amides, this time however achieved from aldoximes reacting via dehydration/hydration mechanism.
14
Oh, Seokjoon. "Graphite-conjugated catalysts : bridging heterogeneous and homogeneous catalysts". Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122714.
Resumen
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2019Cataloged from PDF version of thesis. Page 156 blank.
Includes bibliographical references.
This interconversion occurs via complex multistep, multielectron reactions, which can be carried out by either metallic heterogeneous or molecular homogeneous electrocatalysts. Metallic heterogeneous catalysts have a continuum of electronic states that distribute the redox burden of multielectron reactions, allowing for efficient catalysis. However, heterogeneous catalysts display a variety of active sites and local electronic structures, and are difficult to fine-tune at a molecular level. On the other hand, homogeneous catalysts allow a great degree of synthetic control over the catalytic active site. Moreover, the relative ease in spectroscopic characterization allows a mechanistic understanding of molecular catalysis at a level that is unattainable for heterogeneous catalysis. To bridge the advantages of both types of catalysts, we have developed a surface functionalization strategy for conjugating molecularly well-defined active sites to graphitic carbon surfaces.
First, I will discuss the preparation and characterization of two new types of conjugating N-heterocyclic linkages to graphitic carbon surfaces. This work presents a general method for characterizing modified carbon surfaces with molecular-level structural detail. Then, I will present the electrocatalytic carbon dioxide reduction activity of a graphite-conjugated rhenium catalyst, and compare its catalytic behavior to that of a molecular analog. Electrochemical and spectroscopic data show that graphite-conjugated catalysts do not behave identically to their molecular analogs, but rather show properties similar to that of metallic heterogeneous catalysts, providing a unique bridge between the worlds of heterogeneous and homogeneous catalysis.
Finally, in the appendix, I will present a chapter on the stability of graphite-conjugated linkages under electrochemical polarization, followed by a chapter on catalyzing the reduction of molecular pyridinium species using a graphite-conjugated rhodium catalyst.
by Seokjoon Oh.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Chemistry
15
Evans, P. L. "Ligand design for homogenous catalysis". Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376909.
16
Durrani, Jamie T. "Palladium catalysed asymmetric hydroxy- and alkoxycarbonylation of alkenes". Thesis, University of St Andrews, 2015. http://hdl.handle.net/10023/6276.
Resumen
Palladium catalysed asymmetric hydroxy- and alkoxycarbonylation reactions of alkenes have the potential to deliver valuable chiral carboxylic acid and ester building blocks from cheap feedstocks: alkenes, carbon monoxide and water (alcohols in the case of alkoxycarbonylation). Despite the attractive nature of these reactions, extensive research has so far been unable to produce effective catalysts which are capable of controlling both regio- and enantioselectivity. Building on exciting recent results involving the use of highly enantioselective palladium catalysts derived from Phanephos-type ligands, this research focuses on paracyclophane-diphosphines and their use in asymmetric hydroxy- and alkoxycarbonylation reactions. An investigation into reaction conditions analysed several factors, including solvents, CO-pressure, acidic additives and halide sources, to provide optimal activity and selectivities. Two novel electron-poor paracyclophane-diphosphines and their mono- and di-palladium complexes were synthesised and shown to provide exceptional levels of regioselectivity while maintaining high levels of asymmetric induction. These are the first such examples of hydroxy- or alkoxycarbonylation catalysts to facilitate simultaneous control over both regio- and enantioselectivity. The most effective catalyst was used to promote the reactions of a selection of aryl alkenes and was shown to be tolerant of several different functional groups. A selection of non-symmetric paracyclophane-diphosphine ligands and their palladium complexes were also synthesised and assessed for their performance in hydroxy- and alkoxycarbonylation. We also report the use of Phanephos-type ligands to promote the highly enantioselective hydroxycarbonylation of N-(p-toluenesulfonyl)-3-pyrroline to deliver a chiral proline derivative in high ee.
17
Adams, Nicholas James. "Studies in homogeneous catalysis". Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312264.
18
Downs, Emma. "An Investigation of Transition Metal Catalysts for Cyanohydrin Hydration: The Interface of Homogeneous and Heterogeneous Catalysis". Thesis, University of Oregon, 2014. http://hdl.handle.net/1794/18348.
Resumen
Acrylic monomers are important materials that represent a large portion of the economy. The current industrial synthesis hydrates cyanohydrins with sulfuric acid, a process which results in large amounts of waste and significant energy costs. A transition metal catalyzed, acid free hydration of cyanohydrins would be beneficial from both economic and environmental standpoints. However, this reaction is challenging, as many catalysts are poisoned by the cyanide released when cyanohydrins degrade. Therefore the development of a catalyst that is resistant to cyanide poisoning is the ideal method to circumvent these difficulties.
This dissertation describes several cyanohydrin hydration catalysts, with an emphasis on nanoparticle catalysts. These are at the interface between the homogeneous and heterogeneous catalysts that have been explored previously for this reaction. Chapter I surveys previous studies on nanoparticle catalysts for nitrile hydration and their implications for the hydration of cyanohydrins.
Chapter II reports on the homogeneous platinum catalysts [PtHCl(P(NMe2)3)2] and [PtH2(P(NMe2)3)2], exploring secondary coordination sphere effects to enhance nitrile hydration. Chapter III describes another example of this type of complex, [PtH2(P(OMe)3)2], that forms catalytically active nanoparticles under reaction conditions. Explorations of the reactivity of this catalyst with nitriles and cyanohydrins are also described in this chapter.
Chapter IV investigates a silver nanoparticle catalyst with a water soluble phosphine (1,3,5-triaza-7-phosphaadamantane) ligand for its activity towards the hydration of nitriles and cyanohydrins. The results of the degradation of the nanoparticles in the presence of cyanide are also described. Chapter V reports on the preparation and examination of a solid supported nickel catalyst for cyanohydrin hydration. Finally, Chapter VI describes how these investigations have made progress towards the development of a cyanide resistant nitrile hydration catalyst.
This dissertation includes previously published and unpublished co-authored material.2015-09-29
19
Nicol, Mairi. "Modification of polydienes via homogenous catalysis". Thesis, University of St Andrews, 1998. http://hdl.handle.net/10023/15183.
Resumen
Our investigations into the synthesis of polyketones have involved the catalytic functionalisation of polydienes with particular emphasis on routes via a polyepoxide and a polyalcohol. Initially, a route via the polyepoxide was studied, in which polybutadiene (various micro structures and molecular weights) and polyisoprene were epoxidised (equation 1) in high conversion using a [MoO2CI2 [(lR)-endo]-(+)-3(diethoxyphosphoryl) camphor] catalyst (MoCI2O2L) and subsequently isomerised to the polyketone using lithium bromide [(equation 2), see Scheme 1 in thesis]. Lithium bromide requires a solublising agent in reactions carried out in dichloromethane, however this is not the case for reactions carried out in tetrahydrofuran as lithium bromide is readily dissolved in this solvent. (See abstract in full thesis for equation). Polybutadiene and polyisoprene can be easily converted to their respective polyepoxide. The backbone double bonds of the polydienes show from 1H nmr 100% conversion to the epoxide with greater than 95% selectivity. The polyepoxides are easily purified after the removal of HCl (produced by the catalyst) as this causes crosslinking. Subsequent isomerisation of the purified poly epoxides show from 13C and ir that characteristic ketone units can be formed along with the ketal resonances attributed to brevicomin type moeties, formed from the reaction of a ketone with a neighbouring epoxide group. Problems with the insolubility of the polyketone led to the preparation of a polyalcohol, via hydroboration using 9-borabicyclononane (equation 3) followed by oxidation using an alkaline solution of hydrogen peroxide (equation 4). The attempted dehydrogenation of the polyalcohol to give the resultant polyketone using various oxidants was studied, see Scheme 2. Conversion of the polybutadiene to the alcohol via hydroboration-oxidation using 9-BBN/NaOH-H2O2 showed by 1H and 13C nmr a 50% conversion of the backbone double bonds at a low temperature and 100% conversion at a high temperature. The microstructure of the resultant polyalcohol showed 1,4: 1,5: 1,6 segments in a 1:2:1 ratio, these different segment impart irregularity into the polymer chain and could consequently be carried through to the polyketone giving rise to lower crystallinity and a more processable polymer. Although various oxidants has been investigated for the dehydrogenation of the polyalcohol a suitable oxidant has not yet been found.
20
Groot, Debby de. "Dendrimers as homogeneous transition metal catalysts". [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2001. http://dare.uva.nl/document/58731.
21
Desset, Simon L. "New strategies for the rhodium-catalysed aqueous-biphasic hydroformylation of medium chain alkenes". Thesis, University of St Andrews, 2009. http://hdl.handle.net/10023/842.
Resumen
Aqueous-biphasic organometallic catalysis is, as illustrated by the industrial hydroformylation of propene and butene, one of the most promising ways to overcome the intrinsic problem of catalyst separation in organometallic catalysis. However, for poorly water-soluble substrates, mass transfer limitations bring the reaction rate below any that could be economically viable, greatly limiting the scope of this elegant technology. We have studied three different strategies to overcome this limitation. We developed additives that speed up the reaction whilst retaining fast phase separation and good metal retention. Evidence suggests that those additives affect the reaction by forming emulsions with poor stability under the reaction conditions These emulsions increase the interfacial surface area but break after settling for a short time. We also developed ligands that allow the catalyst to be reversibly transported between an aqueous and an organic phase upon addition and removal of carbon dioxide. This allows the reaction to be carried out under homogeneous conditions, only limited by intrinsic kinetics, and the catalyst to be separated by aqueous extraction triggered by carbon dioxide. The catalyst can be returned to a fresh organic phase by flushing out the carbon dioxide. By applying this methodology for the hydroformylation of medium chain length alkenes, very high reaction rates were obtained and the catalyst could be recycle three times with excellent retention of activity and low metal leaching. This methodology could also be reversed with the reaction being carried out in an aqueous phase in the presence of carbon dioxide and extracting the catalyst into an organic solvent using nitrogen flushing. Finally, we briefly investigated the use of an oscillatory baffled reactor as a mean for mass transfer improvement for aqueous-biphasic hydroformylation. This new type reactor did not improve the performance of the system under the investigated conditions, but may require less energy input for equivalent agitation and mixing.
22
Cooper, Christine J. "Catalysts for stereoselective transformations". Thesis, University of Bath, 2012. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.548099.
23
Maddox, P. J. "Oxidative addition on homogeneous catalysis". Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379910.
24
Garland, Carl Sherman. "Redox promotion of homogeneous catalysis". Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.257734.
25
La, Sorella Giorgio <1987>. "Supramolecular approaches to Homogeneous catalysis". Doctoral thesis, Università Ca' Foscari Venezia, 2015. http://hdl.handle.net/10579/8319.
Resumen
The development of homogeneous systems capable to mimic the enzymes activity is a fundamental topic for catalysis. For that purpose, in this thesis we reported the employment of supramolecular resorcin[4]arene capsule in organic solvents and micelles in water.
The resorcin[4]arene capsule is a spherical hexamer. The high number of electron-rich aromatic rings on the surface of the capsule cause cation-π interactions that confer to the cavity the possibility to accommodate positively charged compounds. We demonstrated that the capsule is also capable to host formally neutral compounds with partial carbene-like electron poor character. In the presence of isocyanides, the empty capsule favoured the nucleophilic attack of either water leading to the formation of the corresponding N-formylamide or trimethylsilylazide leading to the corresponding 1H-tetrazole via the [3+2] cycloaddition. Similarly, in the presence of diazoacetate esters the cavity showed an interesting catalytic activity promoting the 1,3-dipolar cycloaddition with electron-poor alkenes forming N containing heterocyclic compounds.
The interaction of dipolar compounds with capsule was investigated as well using N-oxides as guests. The strong H-bonding acceptor character of N-oxides caused a strong interaction with the hydroxyl groups of the resorcin[4]arene moieties that completely changed the reactivity of the guest with electron-rich aryl isocyanides. The formation of the corresponding diazo-compound as main product in the absence of the capsule moved to the urea derivative with supramolecular host in the reaction solution.
The cation-π interactions within the cavity was exploited to catalyse certain reactions known to involve the formation of cationic intermediates, even though the substrates were not suitable gusts for the cavity. This was the case of the sulfoxidation reaction of thioethers with H2O2 as oxidant and the acid catalysed hydration of alkynes. In both cases the stabilization of the intermediate cationic species within the cavity turned out to be pivotal for the catalytic effect observed.
Micelles are obtained from surfactants that self-assemble in water developing apolar nano-environment in polar media. Micelles made of commercial anionic sulfonated surfactants were employed to stabilize Pd-nanoparticles catalytic systems through a facile, economical and eco-friendly procedure. The achieved catalytic activity showed modulable depending on the surfactant employed, proving effective in hydrogenation, hydro-dehydration and hydrodechlorination reactions in water.
An intensive study was realized in order to find a suitable micellar medium capable to promote the multicomponent synthesis of triazoles from organic bromides, sodium azide and alkynes in a single step reaction. The direct synthesis of triazoles was reached avoiding the employment of the preliminary preparation of dangerous organic azides.
Finally, both supramolecular systems based on micelles in water and resorcin[4]arene in organic solvents were employed to achieve substrate selectivity. Micellar media allowed the preferential conversion of more hydrophobic substrate during competitive Heck and hydrogenation reactions. Conversely, the confined space within the cavity of the resorcin[4]arene capsule was employed to reach the preferential conversion of smaller substrates in the competitive condensation reaction between series of acids and amines with different lengths.
26
Wang, Xia. "Artificial Photosynthesis : Carbon dioxide photoreduction and catalyst heterogenization within solid materials". Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLET025/document.
Resumen
Dans le contexte du réchauffement climatique et de l’usage abusif de combustibles fossiles, la recherche de sources d’énergie propres et durables est l’un des défis les plus importants de notre époque. Récemment, le stockage d’énergie solaire par la réduction de CO2 a fait l’objet d’un nouvel intérêt. Bien que la réduction de CO2 en carburants liquides ou gazeux soit une question à la fois fascinante et fondamentale, sa mise en œuvre dans les dispositifs technologiques reste très difficile à cause de la grande stabilité de CO2 et du caractère endergonique de sa transformation. On outre, les réactions impliquent multiples électrons et protons et ainsi demandent des catalyseurs efficaces et stables pour diminuer les barrières cinétiques importantes.Cette comprend deux parties. Après une introduction, la première partie décrit des études sur des catalyseurs homogènes en combinaison avec un photosensibilisateur, soit séparément soit connecté par liaison covalente. Grâce à la possibilité de les modifier par synthèse et à leur facile caractérisation, les photosystèmes moléculaires homogènes sont plus modulables et peuvent permettre un meilleur contrôle de la sélectivité des réactions et l’étude des mécanismes réactionnels.Cependant, les catalyseurs moléculaires ne peuvent être facilement transposés pour des applications à plus large échelle dans un contexte industriel. En effet, les catalyseurs homogènes sont moins stables et plus difficilement recyclables que les catalyseurs hétérogènes. Dans ce contexte, l’intégration de catalyseurs moléculaires au sein d’un support solide a l’avantage de maintenir leur activité catalytique tout en permettant une séparation et un recyclage plus faciles. La deuxième partie de cette thèse porte donc sur l’immobilisation de catalyseurs moléculaires dans les matériaux. Le but ultime de cette thèse est d’incorporer à la fois le catalyseur et le photosensibilisateur dans le support solideIn the context of global warming and the necessary substitution of renewable energies (solar and wind energy) for fossil fuels, efficient energy-storage technologies need to be urgently developed. Recently, energy storage via the reduction of CO2 has seen renewed interest. Although reduction of CO2 into energy-dense liquid or gaseous fuels is a fascinating fundamental issue, its practical implementation in technological devices is highly challenging due to the high stability of CO2 and thus the endergonic nature of its transformation. Furthermore, the reactions involve multiple electrons and protons and thus require efficient catalysts to mediate these transformations.The objective of this thesis is to investigate different strategies for the storage of solar energy in chemical compounds, through visible-light-driven CO2 reduction. This thesis comprises of two main parts. After an introduction, the first part describes the investigation of homogeneous catalysts in combination with a photosensitizer, either separately or connected covalently. Due to the easily-tunable synthesis and facile characterization of molecular catalysts, homogeneous photosystems are more controllable and can give deep insight into product selectivity and mechanistic issues.With regards to future applicability, however, homogeneous catalysis often suffers from additional costs associated with solvents, product isolation and catalyst recovery, amongst other factors. The integration of molecular catalysts into solid platforms offers the possibility to maintain the advantageous properties of homogeneous catalysts while moving towards practical system designs afforded by heterogeneous catalysis. The second part of this thesis is therefore the immobilization of molecular catalysts within solid materials, namely MOFs and PMO. The ultimate goal of this thesis is to incorporate both catalyst and photosensitizer into the solid support
27
Grootboom, Natasha Denise. "Alkane oxidation using metallophthalocyanine as homogeneous catalysts". Thesis, Rhodes University, 2002. http://hdl.handle.net/10962/d1007794.
Resumen
Iron polychlorophthalocyanine (FePc(Cl)₁₆) and tetrasulfophthalocyanine ([M¹¹TSPc]⁴) complexes of iron, cobalt and manganese are employed as catalysts for the oxidation of cyclohexane using tert-butyl hydroperoxide (TBHP), chloroperoxybenzoic acid (CPBA) and hydrogen peroxide as oxidants. Catalysis using the FePc(Cl)₁₆ was performed in a dimethylformamide:dichloromethane (3 :7) solvent mixture. For the [Fe¹¹TSPc]⁴⁻, [Co¹¹TSPc]⁻ and [Mn¹¹TSPc]⁴⁻catalysts, a water:methanol (1:9) mixture was employed. The products of the catalysis are cyclohexanone, cyclohexanol and cyclohexanediol. The relative percentage yields, percentage selectivity and overall percentage conversion of the products depended on types of oxidant, or catalyst, concentrations of substrate or catalysts and temperature. TBHP was found to be the best oxidant since minimal destruction of the catalyst and higher selectivity in the products were observed when this oxidant was employed. Of the four catalysts investigated [Fe¹¹TSPc]⁴⁻ yielded the highest overall percentage conversion of 20%.The mechanism of the oxidation of cyclohexane in the presence of the FePc(Cl)₁₆ and [M¹¹TSPc]⁴⁻ involves the oxidation of these catalysts, forming an Fe(IlI) phthalocyanine species as an intermediate. Electrocatalysis using [Co¹¹TSPc]⁴⁻ as catalyst, employed an aqueous pH 7 buffer medium for electro-oxidation of 4-pentenoic acid. An enone is suggested as the only oxidation product of 4-pentenoic acid. No degradation of [Co¹¹TSPc]⁴⁻ was observed during the electrocatalytic process. In this process water was used as a source of oxygen therefore eliminating the production of by products from oxidant as in the case of TBHP and CPBA. This system was studied In an attempt to set up conditions for alkane electrocatalytic oxidation.
28
Shinde, Kiran. "Biodiesel production under ultrasound and homogeneous catalysts". Doctoral thesis, Université Laval, 2017. http://hdl.handle.net/20.500.11794/28233.
Resumen
Le biodiesel est obtenu par une réaction de transestérification de triglycérides d’huiles végétales ou des graisses par un monoalcool comme le méthanol. Cette réaction est aussi connue sous la désignation d’alcoholyse. La technique de production de biodiesel sous ultrasons est une nouvelle technologie prometteuse pour cette alternative aux combustibles fossiles. La production de biodiesel sous ultrasons est basée sur l’utilisation de sondes ultrasoniques. En utilisant cette technique, le biodiesel peut être produit à grande échelle. Des techniques d’ultrasonification continue peuvent causer une forte émulsion des phases de l’alcool et d’huile rapidement. Pour un temps de résidence faible, de fortes conversions sont obtenues en présence de différents catalyseurs homogènes. Par conséquent, il est nécessaire de régler les défis restants de la production de biodiesel, en termes de conception de réacteur, de récupération des catalyseurs, de coûts et d’enjeux environnementaux, pour que cette méthode de production de biodiesel devienne une technologie industrielle viable. Les technologies de production de biodiesel étudiées précédemment comportent encore certains défis comme : le problème de récupération du méthanol, la séparation des catalyseurs, le temps de réaction, la température de réaction et les impuretés dans les produits. Donc, il y a toujours un besoin continu pour le développement et la modification des technologies de production du biodiesel. Ce travail abordera le sujet du développement de la production de biodiesel sous ultrasons. L’aspect original des conclusions du travail est la vision par laquelle les ondes ultrasonores affectent la vitesse des réactions de transestérification. Les ultrasons génèrent de fines émulsions du système biphasique dans tout le volume du réacteur. Ceci va évidemment affecter le transfert de masse interphase. Le volume catalytiquement actif est toutefois restreint a une petite zone de réaction située à proximité de la sonde sonotrode. Dans cette fraction du volume, une vitesse de réaction extrêmement élevée est fort probablement associée à des effets de cavitation. Pour augmenter la production de biodiesel par l’éthanol sous ultrasons, nous avons testé les effets possibles d’une addition de méthanol ou d’autres composantes à basse tension de vapeur sur le phénomène accélérant dans les réactions de transestérification des triglycérides, du aux ultrasons. Dans la dernière partie de ce travail, nous avons étudié la réaction de transestérification de l’huile de canola avec du méthanol sur différents types de catalyseurs utilisant à la fois une agitation mécanique et les ultrasons. L’efficacité du transfert de masse dans le champ ultrasonore a amélioré la conversion maximale de transestérification comparativement aux conditions d’agitation mécanique. Dans le cas du propyl-2, 3 dicyclohexylguanidine et 1, 3- dicyclohexyl 2 n-octylguanidine (DCOG) utilisés comme catalyseurs sous ultrasons, les réactions de transestérification que nous avons obtenues ont causé une augmentation notable de la vitesse de conversion des triglycérides. Dams ce cas plus de 80% de récupération de la guanidine dans le mélange réactionnel a été possible en utilisant une colonne d’échange cationique à base de silice. Mots clés: ultrason, transestérification, huile de canola, FAME, méthoxyde de sodium, hydroxyde de sodium, l'hydroxyde de potassium, tétraméthyle d’hydroxyde d’ammonium, Guanidine, colonnes d'échange de cation de silice.Biodiesel is obtained by transesterification reaction of triglycerides from vegetable oils or fats and a mono alcohol like methanol. This reaction is also known as alcoholysis. Ultrasound biodiesel production technique has recently emerged as a promising technology for synthesis of this alternative for fossil fuels. Ultrasound biodiesel production is based on the use of ultrasonic probes. By using this technique biodiesel production can be made on a large scale. Continuous ultrasonication technique can induce strong emulsion of alcohol and oil phases in a short time. Within very small residence time, high conversions are obtained in presence of different homogeneous catalysts. Therefore, it is necessary to solve the remaining challenges of biodiesel production, in terms of reactor design, catalyst recovery, cost and environment issues, in order to address the biodiesel production as a viable industrial technology. The previously studied biodiesel production technologies still show some challenges such as: methanol recovery issue, catalyst separation, reaction time, reaction temperature and oxide impurities in products. Therefore, there is still need to develop and modify the continuous biodiesel production technology. This work deals with the development of ultrasound biodiesel production. The original aspect of the present work conclusions is a vision of how ultrasound waves affect the transesterification reactions rates. Ultrasounds generate a fine emulsion of the biphasic system in the entire reactor volume. This will obviously affect interphase mass transfer. The catalytically active volume is however restricted to a small part of the reaction medium located in the immediate vicinity of the sonotrode probe. Within this volume fraction the extremely high reaction rate is very likely associated with the effects of cavitation. To increase the biodiesel production in presence of ethanol under ultrasound we tested the possible effects of minor methanol or other low vapor tension component additions on the accelerating phenomenon in triglycerides transesterification reactions due to ultrasounds. In the last part of the work we studied the transesterification reaction of canola oil with methanol and different types of catalysts using both mechanical stirring and ultrasonication reaction. The efficiency of mass transfer in the ultrasound field enhanced the higher rate of transesterification reaction as compared to stirring conditions. In case of propyl-2, 3 dicyclohexylguanidine and 1, 3- dicyclohexyl 2 n-octylguanidine (DCOG) as catalysts under ultrasound transesterification reaction we got noticeable TG conversion where as more than 80% regeneration of guanidine is possible from the reaction mixture by using silica cation exchanger columns. Keywords: ultrasound, transesterification, canola oil, FAME, sodium methoxide, sodium hydroxide, potassium hydroxide, Tetramethyl ammonium hydroxide, Guanidine, silica cation exchanger columns.
29
Wojcik, Karolina. "D-glucosamine as "green" substrate in synthesis of ligands for asymetric catalysis". Phd thesis, Université Claude Bernard - Lyon I, 2012. http://tel.archives-ouvertes.fr/tel-00974873.
Resumen
Several ligands derived from D-glucosamine, designed for different catalytic reactions havebeen synthesized. The ligands for homogeneous catalysis based on 1,2-glucodiamine wereprepared, and used in reactions of allylic alkylation, hydrogenation and Michael addition.Supported Aqueous Phase Catalyst (SAPC) system was prepared from D-glucosamine anduse with very good results in Suzuki Miyaura cross coupling reactions. Catalyst was alsorecycled. Attempt to prepare ligands grafted on SBA-silica matrix were made as well asligands containing poly(ethylene) glycol moiety.
30
Funes, Ardoiz Ignacio. "Computational Chemistry for Homogeneous Redox Catalysis". Doctoral thesis, Universitat Rovira i Virgili, 2017. http://hdl.handle.net/10803/456826.
Resumen
Aquesta Tesis Doctoral s'ha centrat en l'estudi computacional mitjançant metodologia DFT (Teoria del funcional de la densitat) de reaccions redox catalitzades en fase homogènia. La primera part recau en l'estudi computacional de dos cicles catalítics d'acoblament oxidatiu. Aquest estudi ha aconseguit desxifrar una de les claus d'aquest tipus de reaccions, l'efecte de l'oxidant extern. Demostrem que en totes dues reaccions, diferents metalls de transició poden col•laborar per a donar una reacció més eficient i selectiva. A més a més, descobrim els factors claus per a la regioselectivitat de les dues reaccions estudiades. La segona reacció va ser estudiada en col•laboració amb el grup experimental del Prof. Frederic Patureau (University of Kaiserslautern).
La segona part de la tesis es centra en canvi en l'estudi teòric de la reacció d'oxidació de l'aigua catalitzada per complexes de la primera serie de transició. S'ha desenvolupat una nova família de catalitzadors mononuclears de coure en col•laboració amb el grup del Prof. Antoni Llobet (ICIQ). S'ha descobert un nou mecanisme de formació de l'enllaç oxígen-oxígen que consisteix en l'atac nucleòfil de l'aigua mitjançant la transferència d'un electró (SET-WNA). Un cop descobert aquest mecanisme, es va veure que també operava sobre altres catalitzadors de coure i ruteni, redefinint així el context mecanístic d'aquesta reacció en catàlisis homogènia.
Aquesta tesis, per tant, proporciona una profunda base mecanística sobre importants reaccions redox mitjançant la química computacional a través dels mètodes DFT.Esta Tesis Doctoral se ha centrado en el estudio computacional mediante metodología DFT (Teoría del funcional de la densidad) de reacciones redox catalizadas en fase homogénea. La primera parte versa sobre el estudio computacional de dos ciclos catalíticos de acoplamiento oxidativo. Este estudio dio con una de las claves en este tipo de reacciones, el efecto del oxidante externo. Demostramos en ambas reacciones como diferentes metales de transición podían colaborar para dar una reacción más eficiente y selectiva. Además descubrimos las claves para la regioselectividad en ambas reacciones. La segunda reacción fue estudiada en colaboración con el grupo experimental del profesor Frederic Patureau (University of Kaiserslautern). Por otro lado, la segunda parte de esta tesis se centra en el estudio teórico de la reacción de oxidación de agua catalizada por complejos de la primera serie de transición. Desarrollamos una nueva familia de catalizadores mononucleares de cobre con la colaboración experimental del grupo del profesor Antoni Llobet (ICIQ), descubriendo un nuevo mecanismo en la formación de enlace oxígeno-oxígeno, el ataque nucleófilo del agua mediante la transferencia de un electrón (SET-WNA). Tras esto extendimos este mecanismo a otros sistemas de cobre y de rutenio, redefiniendo el contexto mecanístico para esta reacción en catálisis homogénea. Esta tesis, por tanto, proporciona una profunda base mecanística sobre el estudio de importantes reacciones redox mediante química computacional a través de los métodos DFT.
This Doctoral Thesis is focused on the computational study by DFT methodology (Density Functional Theory) of homogeneous redox catalized reactions. The first part describes successfully the mechanism of two different catalytic cycles of oxidative coupling reactions. This study found out the explanation about one of the challenging questions on the field, the key role of the external oxidant. We demonstrated the cooperation between different transition metals is essential to catalyze the reaction efficiently and with good selectivities. Additionally, we explained also the regioselectivity of both reactions, in very good agreement with the experimental results. The second reaction was studied in collaboration with the experimental group of professor Frederic Patureau (University of Kaiserslautern). On the other hand, the second part of the thesis is focused on the theoretical study of water oxidation reaction catalyzed by first-row transition metal complexes. Firstly, we developed a new family of mononuclear copper complexes in collaboration with the experimental group of professor Antoni Llobet (ICIQ), discovering a new mechanism for the oxygen-oxygen bond formation step, the water nucleophilic attack. single electron transfer (SET-WNA). From this point, we extended the new mechanism to other catalytic systems based on copper and ruthenium, redefining the mechanistic scenario for the homogeneous catalytic version of this reaction. Therefore, this thesis provides a deep theoretical knowledge abour the homogeneous redox catalysis mechanisms by DFT calculations.
31
Stemp, Michael C. "Homogeneous catalysis in alkaline water electrolysis". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0019/MQ45844.pdf.
32
Taylor, Russell Alan. "Hydrogen bonding effects in homogeneous catalysis". Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.500138.
33
Mitsui, Kazuhiko. "Dendritic Effects in Homogeneous Asymmetric Catalysis". The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1245200227.
34
Patil, R. P. "Studies in homogeneous catalysis: carbonylation reactions". Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 1990. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/3026.
35
Kieffer, Raphaëlle. "Développement de nouveaux catalyseurs pour la dépolymérisation de la lignine par voie d’oxydation". Thesis, Lyon 1, 2015. http://www.theses.fr/2015LYO10124/document.
Resumen
La lignine est l'un des biopolymères les plus importants sur Terre. Elle est extraite des plantes et représente la plus grande source de noyaux aromatiques dans la biomasse. De nombreux projets ayant pour but la dépolymérisation de la lignine en molécules de faibles poids moléculaires, valorisables par les industries chimiques, sont de plus en plus développés au vu du fort potentiel de cette bio-ressource. Le but de notre projet était de développer un nouveau système catalytique pour la dépolymérisation de la lignine. Nous nous sommes intéressés à la conception de nouveaux catalyseurs homogènes et hétérogènes, basés sur la structure connue du complexe Fe(TAML). Nous avons étudié leurs réactivité et stabilité en conditions de catalyse oxydante, et les avons comparés aux caractéristiques du Fe(TAML) existant. Pour ce faire, l'étude catalytique a été réalisée sur des molécules modèles de la lignine, dans le but d'éviter les problèmes analytiques liés à la structure du polymère. Dans un premier temps, nous présenterons la stratégie de fonctionnalisation du ligand TAML connu afin d'obtenir de nouveaux complexes qui puissent être greffés sur un support de silice. Dans un deuxième temps, nous parlerons des résultats de la catalyse oxydante en conditions homogènes et hétérogènes, et de l'influence du changement de la structure des ligands sur l'activité des catalyseursLignin is one of the most abundant biopolymers on earth. It is issued from plants and represents the largest source of aromatics in biomass. Projects aiming at depolymerizing lignin to obtain value-added small molecules for the chemical industry are more and more developed due to the high potential of this bio-resource. The goal of our project was to develop a new catalytic system for the depolymerization of lignin. We have been interested in designing new homogeneous and heterogeneous catalysts based on the known structure of the Fe(TAML) complex. We have studied their reactivity and stability under oxidative catalysis conditions, and have compared them to the characteristics of the existing Fe(TAML). To do so, the catalysis study has been realized on lignin small model molecules to avoid the analytical problems related to a polymer backbone. In a first hand, we will present the strategy of functionalization of the known TAML ligand to design new complexes to be grafted on a silica support. In a second hand, we will talk about the results of oxidative catalysis in homogeneous and heterogeneous conditions, and the influence of the ligand structure change on the activity of the catalysts
36
Dreimann, Jens M. [Verfasser]. "Process Intensification in Homogeneous Catalysis - Catalyst Recovery via Thermomorphic Solvent Systems and Organic Solvent Nanofiltration / Jens M. Dreimann". München : Verlag Dr. Hut, 2017. http://d-nb.info/1139538349/34.
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Dreimann, Jens [Verfasser]. "Process Intensification in Homogeneous Catalysis - Catalyst Recovery via Thermomorphic Solvent Systems and Organic Solvent Nanofiltration / Jens M. Dreimann". München : Verlag Dr. Hut, 2017. http://d-nb.info/1139538349/34.
38
Rahman, Mohd Basyaruddin Abdul. "Energy dispersive EXAFS studies on homogeneous metal catalysts". Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285766.
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Monterio, Mario G. Kool. "Polymerization Studies using homogeneous and supported metallocene catalysts". Thesis, University of Manchester, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.642948.
Resumen
A literature survey of the main aspects of the polymerization of olefins using homogeneous and silica, alumina and niobia supported metallocene catalyst systems is presented. Fundamental information about the surface of niobia and its use as a catalyst support is included. A study of kinetics of polymerization of ethylene was conducted using homogeneous bis(cyclopentadienyl)zirconium dichloride-MAO catalyst systems and its silica, alumina and niobia supported analogue catalyst systems. The characterization of the polyethylene produced by such catalyst systems, focussing on the molecular weight distribution, melting behaviour and morphology of the polymer was carried out.
40
Thevenon, Arnaud. "Homogeneous catalysts for the synthesis of oxygenated polymers". Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:25c312d1-11c9-4180-a62d-b87a41f521c0.
Resumen
This thesis describes the synthesis and characterisation of novel mono and dinuclear homogenous [Zn(II)] and [In(III)] metal complexes. Their applications as catalysts for CO2/epoxide or epoxide/anhydride ring opening copolymerisation and lactide ring opening polymerisation to generate polycarbonates and polyesters, respectively, are also reported. Chapter 3 reports the first indium phosphasalen catalysts for CO2/cyclohexene oxide ring opening copolymerization. The catalysts are active at 1 bar pressure of CO2 and are most effective without any co-catalyst. It is also possible to use the complexes to isolate and characterise the key intermediates in the catalytic cycle. Kinetic and spectroscopic analyses show that polymerisation proceeds via a rare cis-mononuclear coordination- insertion mechanism. Chapter 4 describes a series of mono and dinuclear zinc macrocycle catalysts with very high activities for the racemic lactide ring opening polymerisation. In most cases, the dinuclear zinc catalysts significantly out-perform the mono-zinc homologue. In addition, kinetic and spectroscopic investigations suggest a role for the ligand conformation in mediating rate. The catalysts perform very well under immortal conditions and operate at low catalyst loading, whilst conserving high activities. Chapter 5 presents four dinuclear zinc acetate salen catalysts for the ring opening copolymerisation of CO2/cyclohexene oxide and phthalic anhydride/cyclohexene oxide. The catalysts show moderate activities for CO2/epoxide copolymerisation but are highly active for epoxide/anhydride copolymerisation. Structure/activity relationship studies reveal that the more flexible and electron donating ligand displays the highest activity. Poly(ester-b-carbonate)s are also afforded using the most active catalyst in terpolymerisations of anhydride/epoxide/CO2.
41
Nair, V. S. "Hydroformylation of olefins using homogeneous and biphasic catalysts". Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 1999. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2952.
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Lamb, Gareth W. "Phosphine modified rhodium catalysts for the carbonylation of methanol". Thesis, University of St Andrews, 2008. http://hdl.handle.net/10023/574.
Resumen
The carbonylation of methanol to acetic acid is one of the most important applications in homogeneous catalysis. The first chapter comprises a review on the mechanistic studies into the catalytic cycle of the ‘Monsanto process’ and includes some of the most prominent studies into the use of phosphines in the rhodium-catalysed carbonylation of methanol. The second chapter of this thesis reports on an investigation into the application of rhodium complexes containing several C4 bridged diphosphines, namely BINAP, dppb, dppx and dcpb as catalysts for hydrogen tolerant methanol carbonylation. An investigation into the structure, reactivity and stability of pre-catalysts and catalyst resting states of these complexes has also been carried out. The origin of this hydrogen tolerance is explained based on the differing reactivities of the Rh acetyls with hydrogen gas, and by considering the structure of the complexes. In the third chapter I report on an investigation into how electronic properties and coordination mode affect the elimination of phosphonium salts from rhodium complexes. The stability of a range of monodentate, bidentate and tridentate rhodium-phosphine complexes was tested. I also report on the formation of a novel bidentate complex containing a partially quaternised TRIPHOS ligand and investigate the mechanism of formation using 13CH3I. Strong evidence is also presented supporting a dissociative mechanism as the means of phosphine loss from the rhodium centre. In the final chapters I report an investigation into the stability of rhodium-aminophosphine ligand complexes and into increasing the solubility of potential rhodium pre-catalysts through the use of amine-containing phosphine ligands.
43
Borole, Y. L. "Studies on catalysis and kinetics of hydroformylation reactions by homogeneous catalysis". Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2004. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2889.
44
Motika, Stephen. "Diversifying Homogenous Au(I)-Catalysis through New Reaction Discovery". Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6911.
Resumen
Homogenous Au(I)-catalysis has become a valuable synthetic tool to activate a host of unsaturated carbon functional groups towards nucleophilic addition. Over the course of the past two decades, many have embarked on new journeys within this field. Notably, the advancements in this field hinge on the development of new ligand systems that impart novel reactivity at the metal. Our group has focused on this area, as we have successfully demonstrated the utility of 1,2,3-triazoles as ligands for gold and a host of other transition metals and Lewis acids. With respect to gold catalysis, these ligands enhance the stability of the metal center, thus inhibiting typical reductive decomposition pathways that have plagued this field. The enhanced stability comes with a price though as higher temperatures can be required. We’ve addressed this challenge by discovering an interesting synergy between triazole-gold and Lewis acids, allowing us to overcome the lower reactivity of these catalysts.
During my time as a graduate student, I have focused heavily on enlisting these catalytic systems for new reaction discovery. In my first experimental chapter, I was able to develop an interesting reaction cascade in which triazole-gold and secondary amine catalysts were used. I started with a well-known gold-catalyzed Claisen rearrangement of propargyl vinyl ether, yielding functionalized allenes. The identical oxidation state between these allenes and synthetically appealing dienals was an impetus to develop a new isomerization strategy. After screening various conditions, I was able to successfully execute this design.
Most of the work I have been involved in over the past two years has surrounded a gold-catalyzed hydroboration to yield interesting hetercocycles containing a N-B bond. The N-B bond offers some unique properties as it is isoelectronic to a C-C double bond. Despite the simplicity in this design, it would become apparent early on in this research that mitigating the reducing strength of the starting materials was absolutely critical. Starting materials that were too strongly reducing led to rapid catalyst decomposition. Through thorough reaction screening, we have been able to identify a catalytic system that performs extremely well in this context. Ultimately, our goal in this work is to access 1,2-azaborines, which are isosteres of benzene. This compound exhibits aromaticity, as determined through structural and quantitative analyses by several groups. However, subtle differences in properties between the azaborine and benzene, such as its polarity, have intrigued many researchers across various disciplines. Moreover, the ubiquity of its carbonaceous parent in biological systems has prompted many to pursue new synthetic routes to access 1,2-azaborines.
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Segarra, Maset Maria Dolores. "Switchable and tunable ligands for homogeneous catalysis". Doctoral thesis, Universitat Rovira i Virgili, 2010. http://hdl.handle.net/10803/9110.
Resumen
La presente tesis doctoral trata sobre el desarrollo de ligandos con propiedades inusuales para catálisis homogénea. Para conseguir estas propiedades, se han utilizado diferentes estrategias, por lo que la tesis está dividida en tres partes diferenciadas.En la primera parte se describe el desarrollo de ligandos fosfina que incorporan en su estructura la unidad azobenceno, la cual puede presentar dos isómeros estructuralmente diferentes. Se estudia el efecto de la isomerización sobre diferentes reacciones catalíticas.
En la segunda parte se utilizan interacciones supramoleculares para inducir quiralidad sobre una difosfina biarílica proquiral. Se estudian los complejos supramoleculares formados, así como su efecto en catálisis asimétrica.
En la última parte se describe la obtención de ligandos trans-bidentados. Se sintetizan fosfininas y piridinas monodentadas que forman ligandos bidentados al asociarse mediante enlaces de hidrógeno. Adicionalmente, se incorpora la unidad azobenceno en la estructura de fosfininas y piridinas bidentadas para conseguir la coordinación trans mediante la isomerización del doble enlace.
This thesis describes the development of new ligands with unusual properties to be applied in homogeneous catalysis. Three strategies were envisaged to obtain the the new ligand systems. Accordingly, the thesis is divided in three parts.
The first part describes the design of phosphine ligands that include in their structure the azobenzene moiety, which occurs in two structurally different isomers. The effect of the isomerization on several catalytic reactions was studied.
The second part presents the use of supramolecular interactions to induce chirality in a prochiral biaryl diphosphine. The formation of the supramolecular complexes and the effect on asymmetric catalysis were also investigated.
46
Frew, Jamie J. R. "Novel bulky fluorinated ligands for homogeneous catalysis". Thesis, University of St Andrews, 2008. http://hdl.handle.net/10023/852.
Resumen
A series of novel monodentate and bidentate phosphine ligands substituted with bulky tert-butyl and fluorinated aryl groups have been synthesised. Borane protection has proved to be an excellent method for easy synthesis and purification of bidentate ligands in some cases. However, several of the bulky fluorinated ligands do not form stable borane complexes leading to complications in the synthesis and purification of these compounds. By reaction with transition metal platinum and palladium precursors, it was possible to form dichloride complexes from the synthesised ligands, which were characterised by X-ray crystallography. The complexes were found to be effective catalysts for the hydroxycarbonylation of vinyl arenes (yields of up to 95 % with 3 mol% catalyst). An unsymmetrical bidentate complex (3.18) in combination with paratoluenesulfonic acid and LiCl promoters has given exceptional (for a diphosphine ligand) regioselectivity for the branched acid (98.7 % branched) in the hydroxycarbonylation of styrene. The role of the promoters has been found to be crucial in deciding the activity and selectivity in this reaction.
47
Kelly, Keith. "Homogeneous catalysis routes to heat resistant polymers". Thesis, University of East Anglia, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.257476.
48
Gibbard, Jonathan Peter. "Homogeneous catalysis for the selective hydrogenation of nitroalkenes". Thesis, University of Exeter, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248125.
49
Crawford, Luke. "Mechanistic insights into enzymatic and homogeneous transition metal catalysis from quantum-chemical calculations". Thesis, University of St Andrews, 2015. http://hdl.handle.net/10023/7818.
Resumen
Catalysis is a key area of chemistry. Through catalysis it is possible to achieve better synthetic routes, exploit molecules normally considered to be inactive and also attain novel chemical transformations. The development of new catalysts is crucial to furthering chemistry as a field. Computational chemistry, arising from applying the equations of quantum and classical mechanics to solving chemical problems, offers an essential route to investigating the underlying atomistic detail of catalysis. In this thesis calculations have been applied towards studying a number of different catalytic processes. The processing of renewable chemical sources via homogeneous reactions, specifically cardanol from cashew nuts, is discussed. All routes examined for monoreduction of a diene model by [Ru(H)(iPrOH)(Cl)(C₆H₆)] and [Ru(H)(iPrOH)(C₆H₆)]⁺ are energetically costly and would allow for total reduction of the diene if they were operating. While this accounts for the need of high temperatures, further work is required to elucidate the true mechanism of this small but surprisingly complex system. Gold-mediated protodecarboxylation was examined in tandem with experiment to find the subtle steric and electronic effects that dictate CO₂ extrusion from gold N-heterocyclic carbene activated benzene-derived carboxylic acids. The origin of a switch in the rate limiting step from decarboxylation to protodeauration with less activated substrates was also clearly demonstrated. Studies of gold systems are closed with examinations of 1,2-difluorobenzene C–H activation and CO₂ insertion by [Au(IPr)(OH)]. Calculations highlight that the proposed mechanism for oxazole-derived substrates cannot be extended to 1,2-difluorobenzene and instead a digold complex offers more congruent predicted kinetics. The lens of quantum chemistry was turned upon palladium-mediated methoxycarbonylation reactions. An extensive study was undertaken to attempt to understand the bidentate diphosphine ligand dependency on forming either methylpropanoate (MePro) or copolymers. Mechanisms currently suggested in literature are shown to be incongruous with the formation of MePro by Pd(OAc)₂ and bulky diphosphines. A possible alternative route is proposed in this thesis. Four mechanisms for methoxycarbonylation with Pd(2-PyPPh₂)ₙ are detailed. The most accessible route is found to be congruent with experimental reports of selectivity, acid dependency and slight steric modifications. A modification of 2-PyPPh₂ to 2-(4-NMe₂-6-Me)PyPPh₂ is shown to improve both selectivity and turnover, the latter by four orders of magnitude (highest transition state from 22.9 kcal/mol to 16.7 kcal/mol ∆G), and this new second generation in silico designed ligand is studied for its applicability to wider substrate scope and different solvents. The final chapter of this thesis is a mixed quantum mechanics and molecular mechanics (QM/MM) examination of an enzymatic reaction, discussing the need for certain conditions and the role of particular amino acid residues in an S[sub]N2 hydrolysis reaction.
50
Zafar, Muhammad Naveed. "Development of new ligands for homogeneous transition metal catalysts". Thesis, University of Auckland, 2011. http://hdl.handle.net/2292/7287.
Resumen
This thesis describes the development of new nitrogen donor ligands for homogeneous transition metal catalysis. This includes the synthesis of a macrocyclic ligand with amidate functionality and its palladium complexes, as well as the synthesis and study of acyclic ligands with pyridinium amidate and amide functionality and the palladium complexes of these ligands. Some aspects of the coordination chemistry of the macrocyclic ligand, H4LnBu, which contains pyridine carboxamide groups, were investigated. It was found that palladium metal can be selectively inserted in to head or tail region of macrocycle depending on the conditions employed. Palladium(II) migrates from the tail to the head region on heating in the presence of bases like DBU, NH2Lac[7] and n-butyl amine. The water molecule coordinated to palladium in Pd(H2LnBu)(OH2) can be displaced by nitrogen donor ligands such as N-(3-aminopropyl)caprolactam (NH2Lac), nbutylamine (NH2Bu), and DBU. DBU coordinated to palladium in the head region of the macrocycle can also be displaced by N-(3-aminopropyl)caprolactam and nbutylamine. Hydrolysis of DBU to give NH2Lac occurs during the formation of Pd(H2LnBu)(NH2Lac[7]) from either H4LnBu or Pd(OAc)(H3LnBu). However the coordinated DBU in Pd(H2LnBu)(DBU) does not undergo hydrolysis. Studies showed that it is the acetic acid that is formed during the coordination of the palladium acetate to the macrocycle that catalyses the hydrolysis of DBU. A new class of nitrogen donor ligands, the pyridinium amidates, was studied and found to be strong σ-donor ligands. These were synthesised by deprotonation of the corresponding N-protonated compounds either by using sodium hydride or aqueous sodium hydroxide base. DFT calculations and X-ray crystallography results clearly indicate that the pyridinium amidate ligands exist predominantly in imine resonance form and there is restricted rotation about exocyclic C=N. The strong σ-donor properties of this type of ligand were evidenced by the very low average ν(CO) value displayed by cis-Rh(L1{R2})(CO)2Cl and this is amongst the lowest average ν(CO) value recorded for rhodium complexes of the type cis-Rh(L)(CO)2Cl, where L is a neutral ligand. The rhodium complex, Rh(L1{R2})(CO)2Cl, was formed by direct reaction of rhodium carbonyl chloride dimer, [RhCl(CO)2]2, with the pyridinium amidate ligand. However pure palladium complexes could be prepared more conveniently through the reaction between Pd(COD)Cl2 and the N-protonated ligand after addition of the base DBU, which presumably serves to generate the pyridinium amidate in situ. Long Pd-Cl bond distances were found in complexes where the trans ligand was a pyridinium amidate nitrogen. This indicates this nitrogen donor ligand typically has a strong trans influence. The comparison of these pyridinium amidate ligands with pyridinium amide and NHC ligands showed that the structural and electronic properties of all these ligands are very similar. In order to compare the reactivity of pyridinium amidate ligands with closely related pyridinium amide ligands, new pyridinium amide ligands analogous to pyridinium amidates were prepared by an alternative route to those previously reported in literature. This involved a solid state reaction between 4-chloro-N-methyl pyridium triflate and the corresponding amine at 200 to 250oC followed by deprotonation of the N-protonated ligands with sodium hydride or sodium hydroxide in dichloromethane. Palladium complexes of these ligands were prepared by employing similar method to the one used for the synthesis of pyridinium amidate palladium complexes. The new palladium complexes were investigated for catalytic activity in the Heck-Mizoroki and Suzuki-Miyaura coupling reactions. Comparative studies showed that pyridinium amidate ligands are better supporting ligands for above mentioned coupling reactions than pyridinium amides. The stability of the complexes under catalytic conditions was judged on the basis of the formation of visible palladium black during the reactions. It was found that palladium pyridinium amidate complexes were more stable than palladium pyridinium amide complexes under the conditions used for the Heck- Mizoroki and Suzuki-Miyaura coupling conditions. It was also found that the presence of a chelating pyridyl group clearly improves the stability of the palladium pyridinium amidate complexes under these conditions.