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1
Salim, Sofia Saima. "Synthesis of sulfamides using ring closing diene metathesis and enyne metathesis." Thesis, University of Southampton, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417402.
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Nieczypor, Piotr. "Immobilisation of Ru-based metathesis catalysts and related aspects of olefin metathesis." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2004. http://dare.uva.nl/document/74260.
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Rountree, S. M. "Metal catalysed olefin metathesis." Thesis, Queen's University Belfast, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.517512.
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Oakley, Garrett W. "Solid-state olefin metathesis." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0007900.
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Courchay, Florence C. "Metathesis and isomerization activity of ruthenium carbene catalysts in acyclic diene metathesis polymerization." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0012985.
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Vernall, Andrea J. "Cross Metathesis and Ring-Closing Metathesis Reactions of Modified Amino Acids and Peptides." Thesis, University of Canterbury. Chemistry, 2005. http://hdl.handle.net/10092/5798.
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This thesis investigates the application of cross metathesis and ring-closing metathesis to amino acid and peptide-based substrates that are suitably modified to contain an olefin tether.
Chapter One introduces olefin metathesis, describes the mechanism of cross metathesis (CM) and ring-closing metathesis (RCM), and outlines the catalysts that can be used for these transformations. The application of CM and RCM to amino acid and peptide-based systems is reviewed.
Chapter Two describes the CM coupling between modified lysine- (2.34 - 2.37, 2.43), serine- (2.45, 2.46), and cysteine-based (2.48, 2.49a, 2.51) amino acids and dipeptides (2.54, 2.57) to a terminal alkene (2.61, 2.65), carbohydrate (1.51b), or fatty acid (2.76) target compound using catalyst 1.17. The amino acid and dipeptide-based CM substrates were prepared by side-chain acylation of the parent amino acid with carboxylic acids containing variable but controllable olefin tether lengths. A CM model study in which these amino acid-based substrates were coupled to terminal alkene 2.61 and 2.65 gave CM products 2.66 - 2.74. CM was then carried out between amino acid-based substrates and a carbohydrate (1.51b) or fatty acid derivative (2.76), that afforded a novel series of glycoamino acids (2.80 - 2.85) and lipoamino acids (2.94 - 2.101).
Chapter Three describes the synthesis of amino acid dimers by CM. Two serine-based (3.22 - 3.23) and two cysteine-based (3.24 - 3.25) symmetrical dimers along with two unsymmetrical serine-cysteine dimers (3.26 - 3.27) were prepared from the same side-chain acylated amino acid substrates described in chapter 2. These compounds are examples of novel cross-linked amino acid-based dimers, and further illustrate the versatility of the CM methodology developed in this thesis.
Chapter Four describes the synthesis of cyclic amino acids and dipeptides via RCM of acyclic precursors that are suitably modified with acyl olefin tethers of variable length. Cyclic compounds based on lysine (4.6, 4.13), serine (4.31, 4.33), and cysteine (4.40, 4.42) single amino acid residues, and compounds based on lysine (4.16, 4.21, 4.27), serine (4.37), and cysteine (4.45, 4.46) dipeptides were prepared. All these compounds were constructed using the same, versatile general method, which involves acylation of the natural amino acid substrate with a carboxylic acid of controllable olefin tether length followed by RCM with catalyst 1.17 to give cyclic products containing variable ring sizes.
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Alheritiere, Cyrille. "Electrodialysis applied to metathesis reactions." Thesis, Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/11697.
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Al-Samak, Basma. "Alternating ring-opened metathesis copolymers." Thesis, Queen's University Belfast, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343280.
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Thompson, Jillian Margaret. "Olefin metathesis polymers and copolymers." Thesis, Queen's University Belfast, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314162.
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Tyler, Michelle A. "Mechanistic studies of metathesis polymerisations." Thesis, Aston University, 1987. http://publications.aston.ac.uk/14525/.
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Ward, Donald William Bercaw John E. "Stereoselective ruthenium-catalyzed olefin metathesis /." Diss., Pasadena, Calif. : California Institute of Technology, 2004. http://resolver.caltech.edu/CaltechETD:etd-07152003-183214.
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Huang, Zheng Brookhart Maurice S. "Alkane metathesis via tandem catalysis." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2009. http://dc.lib.unc.edu/u?/etd,2576.
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Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2009.Title from electronic title page (viewed Oct. 5, 2009). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Chemistry." Discipline: Chemistry; Department/School: Chemistry.
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Butler, Lynnika. "Prosodically Driven Metathesis in Mutsun." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/311476.
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Among the many ways in which sounds alternate in the world's languages, changes in the order of sounds (metathesis) are relatively rare. Mutsun, a Southern Costanoan language of California which was documented extensively before the death of its last speaker in 1930, displays three patterns of synchronic consonant-vowel (CV) metathesis. Two of these patterns appear to have remained productive while the language was actively spoken. In stem-deriving metathesis, many disyllabic noun stems ending in a VC string (as well as a few trisyllabic noun stems) alternate with semantically related verb stems ending in a CV string: e.g.,cayic ‘strength’ ~ cayci ‘to be strong’. In reflexive metathesis, a subset of verb stems, which are normally vowel-final in all environments, surface in consonant-final form in the presence of the reflexive suffix –pu and/or the reciprocal suffix -mu, as in kitro ‘to dress, to clothe’ ~ kitorpu ‘to get dressed, to dress oneself’. Finally, in suffix metathesis, the plural and locative suffixes (as well as the desiderative/irrealis enclitic) alternate between CCV and CVC forms depending on whether the preceding stem ends in a consonant or a vowel. Based on data from a large corpus of archival records of the language compiled over a span of more than a century, all three patterns of metathesis in Mutsun appear to defy the types of phonological analysis that have been proposed in the literature to account for metathesis in a variety of other languages. The phonetic and phonological factors claimed to motivate metathesis in other languages, such as misinterpretation of acoustic cues, stress attraction, sonority hierarchies, and positional restrictions, are absent in Mutsun. In this dissertation, I argue that prosodic analyses based on syllable weight and prosodic templates are required to account for Mutsun metathesis. Mutsun stem metathesis in particular has less in common, morphophonologically speaking, with metathesis in other languages than it does with reduplication or templatic morphology.
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Blackwell, Helen Elizabeth Grubbs Robert H. "New synthetic applications for ring-closing metathesis and cross-metathesis employing well-defined ruthenium alkylidenes /." Diss., Pasadena, Calif. : California Institute of Technology, 1999. http://resolver.caltech.edu/CaltechETD:etd-09262005-133922.
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Lummiss, Justin Alexander MacDonald. "Olefin Metathesis: Life, Death, and Sustainability." Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/32277.
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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.
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Gomes, Vincent G. (Vincent Gracias). "Physisorption and diffusion in propene metathesis." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74531.
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Propene metathesis on Re$ sb2$O$ sb7$/$ gamma$-Al$ sb2$O$ sb3$ catalyst was selected for characterizing the simultaneous effects due to multicomponent physisorption, diffusion and reaction under ambient conditions. Analytical solutions to mathematical models for single component physisorption-diffusion systems were validated by comparing against experimental data obtained in a previous work. The accuracy of the numerical solution, obtained by orthogonal collocation within the method of lines, was evaluated by comparing against the analytical solutions. The single-component models were extended to the multicomponent system. Multicomponent physisorption equilibria were predicted by applying the Ideal Adsorbed Solution theory. The effective diffusivities for ethene, propene and 2-butene were calculated from Knudsen, molecular and surface diffusivities. The pore and surface tortuosity factors were estimated from the porosity data. The reaction rate expression was based on the carbene mechanism.Transient experiments were performed in a Berty reactor under computer control, implemented in FORTH (programming language), under interrupt-driven multi-tasking mode. The original reactor impeller was modified to provide improved mixing performance. Active Re$ sb2$O$ sb7$/$ gamma$-Al$ sb2$O$ sb3$ catalysts were prepared and characterized for BET surface area, pore size, surface morphology (SEM) and composition (ESCA). Ethene metathesis was observed under ambient conditions over Re$ sb2$O$ sb7$/$ gamma$-Al$ sb2$O$ sb3$ catalyst. Toth and Extended Langmuir isotherms were fitted to pure component physisorption data. The predictions from the distributed variable models, compared reasonably with the transient experiments for physisorption-diffusion with single, binary and ternary component systems. The reaction kinetics was identified by solving the inverse problem in conjunction with data from transient experiments. The constrained Levenberg-Marquardt techniques with QR and singular value decompositions were employed for solving the inverse problem. Nonisothermal model equations were also solved. The model predictions were evaluated against transient experiments under conditions different from those used for estimating the parameters.
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Subramaniam, Arumugam. "Study and optimisation of metathesis catalysts." Thesis, Brunel University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339327.
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Orr, Allan J. "A metathesis approach to aromatic heterocycles." Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433342.
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Banti, Donatella. "Ene-Yne metathesis of norbornene derivatives." Thesis, King's College London (University of London), 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.411341.
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Spandl, Richard Joseph. "Diversity oriented synthesis using enyne metathesis." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611971.
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Standen, Patricia E. "Metathesis routes to carbocyclic frame works." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/13204.
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The addition of allyl magnesium and allyl indium reagents to a key TBS protected norbornenyl building block, synthesised in 6-steps from commercially available 1,1-dimethoxy-2,3,4,5-tetrachlorocyclo-pentadiene, has been achieved providing the syn addition products with high diastereoselectivity. The subsequent exposure of the addition products to metathesis conditions, in the presence of ethylene, then provided cis fused [3.0.3]-carbocycles with very high regioselectivity, via a Ring Rearrangement Metathesis (RRM) transformation. The high level of regioselectivity is due to the rearrangement of the metathesis intermediates to give the more thermodynamically stable product This work has been expanded to include [2.2.2]-bicycles, addition of allyl magnesium and indium reagents to a key bicyclo[2.2.2]oct-5-en-2-one has been achieved, giving both diastereoisomers, separable by chromatography. The subsequent exposure of the addition products to optimised metathesis conditions, then provided cis fused [3.3.1] carbocycles with very high regioselectivity, via a RRM transformation. It was found that two possible cyclisation pathways occur under our reaction conditions; pathway (a) will yield a cis-fused [4.0.3]-carbocycle while pathway (b) will deliver the observed [3.3.1]-carbocycle.
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liu, lei. "Polypropylene block copolymer synthesis by metathesis." University of Akron / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=akron1625523936334755.
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Gorodetskaya, Irina A. Tirrell David A. Grubbs Robert H. "Nonlinear polymeric architectures via olefin metathesis /." Diss., Pasadena, Calif. : California Institute of Technology, 2009. http://resolver.caltech.edu/CaltechETD:etd-04262009-232200.
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Xu, Chaofan. "New Ru-Based Catalysts and Strategies for Kinetically Controlled Stereoselective Olefin Metathesis:." Thesis, Boston College, 2020. http://hdl.handle.net/2345/bc-ir:109015.
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Thesis advisor: Amir H. HoveydaChapter 1. In Situ Methylene Capping: A Key Strategy in Catalytic Stereoretentive Olefin MetathesisA general approach for in situ methylene capping that significantly expands the scope of catalyst-controlled stereoselective olefin metathesis is presented. By incorporation of stereodefined 2-butene as the capping reagent, the catechothiolate Ru complex is enabled to catalyze olefin metathesis reactions of terminal alkenes. Substrates bearing a carboxylic acid, an aldehyde, an aryl substituent, an α substituent were thus converted to the desired products in 47–88% yield and 90:10–98:2 Z:E selectivity. The capping strategy was also applied in ring-closing metathesis reactions leading to 14- to 21-membered macrocyclic alkenes (96:4–98:2 Z:E). The utility of this method was highlighted through synthesis of a platelet aggregate inhibitor and two members of the prostaglandin family compounds by cross-metathesis reaction, as well as a strained 14-membered ring stapled peptide by macrocyclic ring-closing metathesis. Examples of the corresponding E-selective cross-processes are provided as well. Chapter 2. Synthesis of Z- or E-Trisubstituted Allylic Alcohols and Ethers by Kinetically Controlled Catalytic Cross-MetathesisKinetically controlled Ru-catalyzed cross-metathesis reactions that generate Z- or E-trisubstituted alkenes are discussed. Reactions were catalyzed by catechothiolate Ru complex to generate trisubstituted allylic alcohols and ethers in up to 81% yield and >98% stereoisomeric purity. The approach is applicable to synthesis of products containing an alcohol, an aldehyde, a carboxylic acid or an alkenyl substituent. Mechanistic models that account for the observed trends in efficiency and stereoselectivity will be provided. Chapter 3. A New Ru-Based Catechothiolate Complex Bearing an Unsaturated NHC Ligand for Synthesis of Z-α,β-Unsaturated Carbonyl Compounds by Cross Metathesis Design and development of a new Ru catechothiolate complex that may be used to promote Z-selective cross-metathesis transformations that afford Z-α,β-unsaturated esters, acids, and amides (including Weinweb amides) are discussed. Comparison between Ru catechothiolate complexes with an unsaturated NHC and a saturated NHC ligand will be provided. Utility of the approach is demonstrated by an eight-step synthesis (15% overall yield) of an intermediate for synthesis of stagonolide E, and a five-step synthesis of a precursor to dihydrocompactin
Thesis (PhD) — Boston College, 2020
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
25
Day, Craig. "Efficient New Routes to Leading Ruthenium Catalysts, and Studies of Bimolecular Loss of Alkylidene." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/38675.
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Olefin metathesis is an exceptionally versatile and general methodology for the catalytic assembly of carbon-carbon bonds. Ruthenium metathesis catalysts have been widely embraced in academia, and are starting to see industrial uptake. However, the challenges of reliability, catalyst productivity, and catalyst cost have limited implementation even in value-added technology areas such as pharmaceutical manufacturing. Key to the broader adoption of metathesis methodologies is improved understanding of catalyst decomposition. Many studies have focused on phenomenological relationships that relate catalyst activity to substrate structure, and on the synthesis of new catalysts that offer improved activity. Until recently, however, relatively little attention was paid to catalyst decomposition. The first part of this thesis explores a largely overlooked decomposition pathway for “second-generation” olefin metathesis catalysts bearing an N-heterocyclic carbenes (NHC) ligand, with a particular focus on identifying the Ru decomposition products. Efforts directed at the deliberate synthesis of these products led to the discovery of a succinct, high-yielding route to the second-generation catalysts.
Multiple reports, including a series of detailed mechanistic studies from our group, have documented the negative impact of phosphine ligands in Ru-catalyzed olefin metathesis. Phosphine-free derivatives are now becoming widely adopted, particularly in pharma, as recognition of these limitations has grown. Decomposition of the phosphine-free catalysts, however, was little explored at the outset of this work. The only documented pathway for intrinsic decomposition (i.e. in the absence of an external agent) was -hydride elimination of the metallacyclobutane (MCB) ring as propene. An alternative mechanism, well established for group 3-7 and first-generation ruthenium metathesis catalysts, is bimolecular coupling (BMC) of the four-coordinate methylidene intermediate. However, this pathway was widely viewed as irrelevant to decomposition of second-generation Ru catalysts. This thesis work complements parallel studies from the Fogg group, which set out to examine the relevance and extent of BMC for this important class of catalysts. First, -hydride elimination was quantified, to assess the importance of the accepted pathway. Even at low catalyst concentrations (2 mM Ru), less than 50% decomposition was shown to arise from -hydride elimination. Parallel studies by Gwen Bailey demonstrated ca. 80% BMC for the fast-initiating catalyst RuCl2H2IMes(=CHPh)(py)2 GIII. Second, the ruthenium products of decomposition were isolated and characterized. Importantly, and in contrast to inferences drawn from the serendipitous isolation of crystalline byproducts (which commonly show a cyclometallated NHC ligand), these complexes show an intact H2IMes group. This rules out NHC activation as central to catalyst decomposition, suggesting that catalyst redesign should not focus on NHC cyclometallation as a core problem. Building on historical observations, precautions against bimolecular coupling are proposed to guide catalyst choice, redesign, and experimental setup.
The second part of this thesis work focused on the need for more efficient routes to second-generation Ru metathesis catalysts, and indeed a general lack of convenient, well-behaved precursors to RuCl2(H2IMes). This challenge was met by building on early studies in which metathesis catalysts were generated in situ by thermal or photochemical activation of RuCl2(p-cymene)(PCy3) in the presence of diazoesters. Such piano-stool complexes (including the IMes analogue) have also been applied more broadly as catalysts, inorganic drugs, sensors, and supramolecular building blocks. However, RuCl2(p-cymene)(H2IMes), which should in principle offer access to the RuCl2(H2IMes) building block, has been described as too unstable for practical use. The basis of the instability of RuCl2(p-cymene)(H2IMes) toward loss of the p-cymene ring was examined. Key factors included control over reaction stoichiometry (i.e. limiting the proportion of the free NHC), limiting exposure to light, and maintaining low concentrations to inhibit bimolecular displacement of the p-cymene ring. A near-quantitative route to RuCl2(p-cymene)(H2IMes) was achieved using appropriate dilutions and rates of reagent addition, and taking precautions against photodecomposition. This approach was used to develop atom-economical syntheses of the Hoveyda catalyst, RuCl2(H2IMes)(=CHAr) (Ar = 2-isopropoxybenzylidene) and RuCl2(H2IMes)(PPh3)(=CHPh), a fast-initiating analogue of GII. Related p-cymene complexes bearing bulky, inflexible imidazolidene or other donors may likewise be accessible.
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Lehman, Stephen E. "Ruthenium catalysis in metathesis polymerization synthesis of linear copolymers of ethylene and polar vinyl monomers via metathesis /." [Gainesville, Fla.] : University of Florida, 2003. http://purl.fcla.edu/fcla/etd/UFE0001021.
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Zhugralin, Adil R. "Combined Theoretical and Experimental Investigation of N-Heterocyclic Carbenes as Lewis Base Catalysts and as Ancillary Ligands in Ru-Catalyzed Olefin Metathesis. Mechanistic Investigation of Fluxional Behavior of Ru-Based Olefin Metathesis Catalysts." Thesis, Boston College, 2011. http://hdl.handle.net/2345/2973.
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Thesis advisor: Amir H. HoveydaChapter 1. Through the use of quantum theory of atoms in molecules (QTAIM) the similarities and differences between transition metal complexes ligated by phosphines and N-heterocyclic carbenes (NHC) were elucidated. Among the key findings, the phosphines were identified as stronger charge donors than NHCs; however, the latter class of ligands exhibits a weaker p-accepting character than the former. Furthermore, Tolman electronic parameter (TEP) was determined to be an inadequate gauge for the total electron donating ability of phosphines and NHCs; rather TEP can serve as a measurement of population of dp set of orbitals of a metal center in question. Computational and experimental studies of the mechanism of NHC-catalyzed boron and silicon addition to a,ß-unsaturated carbonyls reactions were carried out. Through the use of radical traps the mechanisms involving homolytic cleavage of B-B or B-Si bonds were ruled out. Computational (DFT) studies of the mechanism identified two pathways: (1) direct activation of diboron or borosilyl reagents through coordination of NHC to the B atom, (2) net oxidative addition of the diboron or borosilyl reagents to the carbon (II) of the NHC. The insights gained from the aforementioned studies were employed to rationalize the observed lack of reactivity of NHC-activated diboron complexes in the presence of aldehydes. Chapter 2. New C(1)-symmetric chiral monodentate N-heterocyclic carbenes were prepared, and corresponding chiral Ru-carbene complexes were synthesized. These complexes were employed to gain empirical understanding of factors that govern stereoselectivity in Ru-catalyzed enantioselective olefin ring-closing metathesis. The data thus obtained was employed to infer that syn-to-NHC reaction pathways are competitive and non-selective. One plausible mechanism, through which syn-to-NHC pathways can be accessed, involves Berry pseudorotations. Through the use of stereogenic-at-Ru complexes diastereomeric Ru-carbenes were isolated (silica gel chromatography) and spectroscopically characterized in solution phase. The diastereomeric Ru-carbenes were found to undergo non-metathesis stereomutations at Ru center, thereby providing additional support for the above hypothesis regarding accessibility of syn-to-NHC olefin metathesis pathways. Non-metathesis stereomutation at Ru was found to be accelerated in the presence of protic additives, suggesting the plausibility of hydrogen bonding between the acidic proton and the X-type ligands on Ru. Occurrence of hydrogen bonding was corroborated through the use of chiral allylic alcohols in Ru-catalyzed diastereoselective ring-opening/cross metathesis, which was developed into a versatile method for highly diastereoselective functionalization of terminal olefins
Thesis (PhD) — Boston College, 2011
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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Marleau-Gillette, Joshua. "Studies of Metathesis for Materials Applications: Present and Future Possibilities." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/23702.
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Compounds containing multiple metal-carbon bonds are now widely used as catalysts for organic and materials synthesis. Among such transformations, olefin metathesis (OM) occupies a position of pre-eminent significance. Alkyne metathesis holds great promise, but remains in a much lower state of development. The OM-directed work in this thesis sought to advance the state of the art in living, Ru-catalyzed ringopening metathesis polymerizations (ROMP). Currently, the first- and third-generation Grubbs initiators, which exhibit the ease of handling characteristic of the late metal ruthenium, dominate ROMP applications. These initiators are characterized by extremes of reactivity, however. We describe the first ruthenium initiator capable of living ROMP at RT, irrespective of monomer bulk. Polydispersity indices as low as 1.03 are routinely attainable, and excellent control is maintained in synthesis of diblock copolymers from sterically demanding and sterically unencumbered monomers. Work on alkyne metathesis sought to expand existing understanding of the features that influence stability and reactivity in ruthenium carbynes. A classification system was developed in which Class A carbynes were defined as those that readily undergo conversion into an M=C entity (e.g. vinylidene, allenylidene, or alkylidene); Class B carbynes those that have a stable carbyne functionality. Four Ru carbyne complexes, all initially regarded as prospective Class B carbynes, were selected for study. Investigation of their reactivity resulted in categorization of several as Class A species, and development of design criteria that may open the door to assembly of stable, well-defined carbyne complexes of ruthenium.
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Ireland, Benjamin. "Amines in Olefin Metathesis: Ligands and Poisons." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/34342.
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Olefin metathesis is a powerful tool for assembly of carbon-carbon bonds. Amines and related N-donors are problematic functional groups in Ru-catalyzed olefin metathesis - a well- documented, but poorly understood problem.
The first part of this thesis focuses on amine-induced deactivation pathways; two of which are described in depth. Alkylidene abstraction, a previously unknown reaction for nitrogen nucleophiles, was observed for smaller and less Bronsted-basic amines. Deprotonation of the metallacyclobutane intermediate formed during catalysis is prominent for highly Bronsted basic or sterically bulky N-donors. Monosubstituted (and, by extension unsubstituted) metallacyclobutanes are particularly vulnerable to deprotonation.
For each pathway, the fate of the alkylidene Ru=CHR functional group proved key in determining the nature of deactivation. Both pathways have been detected during catalysis, as evidenced by formation of diagnostic amine (RCH2NR2’) or substituted propene products. A combination of quantitative NMR and GC-MS analysis was used to identify these species on loss of the Ru-alkylidene functional group.
The second part of this thesis focuses on incorporating amines into catalyst design – an under-utilized strategy in the context of Ru-catalyzed olefin metathesis. A modified Grubbs-type catalyst was developed featuring a bulky, relatively non-basic biaryldiamine ligand. Metathesis activity for this catalyst was comparable, and in some cases superior to the most widely-used homogeneous catalysts currently available. Several new, related Ru-benzylidenes were also prepared and fully characterized in conjunction with the mechanistic studies described above.
Progress toward development of N-anion-containing metathesis catalysts is also discussed. Synthesis of Ru-hydride complexes originally intended for this purpose allowed for a fundamental study of the coordination chemistry and reductive elimination chemistry of the NPh2– anion.
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Higman, Carolyn Sarah. "Isomerization in Olefin Metathesis: Challenges and Opportunities." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/34435.
Full textAbstract:
The past two years have witnessed groundbreaking advances in the industrial deployment of olefin metathesis. While metathesis methodologies have been an integral part of the chemical manufacturing landscape for 60 years, implementation in pharmaceutical and specialty chemicals manufacturing represents a new frontier. The imperative to develop greener and more cost-effective manufacturing processes is anticipated to spur further improvements in sustainable synthesis. Advances in catalyst productivity, however, are critical to expansion of the uptake of metathesis methodologies in this and other manufacturing sectors.
Key to increased catalyst productivity is elimination of side reactions that lower yield and errode selectivity. Among such reactions, double-bond isomerization is by far most common. Accumulating evidence suggests that unwanted isomerization during olefin metathesis is due to ruthenium species generated via catalyst decomposition. The identification of these species and how they are formed is thus of great importance. Two hydride complexes, RuHCl(CO)(H2IMes)(PCy3) and a dinuclear hydride, are known to form under some circumstances by decomposition of the second-generation Grubbs catalyst, RuCl2(H2IMes)(PCy3)(=CHPh), GII. These complexes have been widely viewed as responsible for unintended isomerization reactions. However, examination of their performance in olefin isomerization under conditions relevant to metathesis reveals that their activity is too feeble to account for the levels of isomerization observed during metathesis. Alternatively, kinetically competent culprits emerge from decomposition studies that reveal unexpected ruthenium products on decomposition of GII during metathesis; specifically, formation of ruthenium nanoparticles. The formation and catalytic non-innocence of RuNPs constitutes a new paradigm in this field, which opens the door to new approaches to prevent or to harness olefin isomerization. Key to prevention, clearly, is circumventing the decomposition pathways that enable ligand stripping from the active catalyst. New approaches to catalyst design that involve use of truncated NHC ligands are also examined. Finally, the power and utility of isomerization when coupled with metathesis is explored. The opportunities and limitations of orthogonal isomerization–metathesis catalysis are examined in the context of the two-step synthesis of cinnamates from 1-allylbenzenes abundant in essential oils. An efficient one-pot, two-catalyst protocol is developed for conversion of these biorenewable feedstocks to high-value-added chemicals.
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Snowden, David George. "Ring-opening metathesis polymerisation of substituted norbornadienes." Thesis, Queen's University Belfast, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282338.
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Maechling, Simon. "Synthesis of peptide mimetics via olefin metathesis." Thesis, University of Reading, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413575.
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Hector, Andrew Lee. "Self propagating metathesis preparations of inorganic materials." Thesis, University College London (University of London), 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243565.
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Coulson, Bethan. "Sigmatropic rearrangement-metathesis based approaches to cyclopentadienes." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/59037.
Full textAbstract:
This thesis is divided into four chapters. Chapter one is a review of cyclopentadienes (Cps), and is split by sub-classification of applications in organometallics, applications in organic methodology, synthesis of complex Cps from post carbocycle modification and de novo synthesis of Cp. Chapter two introduces the decarboxylative Claisen rearrangement (dCr) and details investigations of the application of this reaction towards Cp synthesis using three different activating groups. Chapter three focuses on the decarboxylative Claisen rearrangement (dCr) from a computational aspect. It begins with a brief review of the mechanism of the [3,3]-sigmatropic rearrangement and examples of density functional theory (DFT) to rationalise Ireland-Claisen rearrangements. The kinetic data of [3,3]-sigmatropic rearrangement of tosyl malonates is studied and compared to DFT calculations. The method devised is tested on literature dCr reactions and then used predictively to interpret synthetic outcomes. Chapter four provides experimental procedures and characterisation data.
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Lin, Yuya Angel. "Olefin metathesis for site-selective protein modification." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:37d998f6-c1cd-4e2c-9f9f-89d197d21016.
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Site-selective protein modification has become an important tool to study protein functions in chemical biology. In the preliminary work, allyl sulfides were found to be reactive substrates in aqueous cross-metathesis (CM) enabling the first examples of protein modification via this approach. In order to access the enhanced CM reactivity of allyl sulfide on proteins, facile chemical methods to install S-allyl cysteine on protein surface were developed. In particular, a cysteine-specific allylating reagent – allyl selenocyanate was used on protein substrate for the first time. The substrate scope of allyl sulfide-tagged proteins and factors that affect the outcome of CM was also investigated. A range of metathesis substrates containing different olefin tether of various lengths were screened; allyl ethers were found to be most suitable as CM partners. By reducing the steric hindrance around the allyl sulfide on protein surface through a chemical spacer, the rate and conversion of metathesis reaction on proteins was greatly enhanced. Moreover, allyl selenides were found to be more reactive than allyl sulfides in CM and enabled reactions with substrates that were previously impossible for the corresponding sulfur-analogue. Through this work, substrate selection guidelines for successful metathesis reaction on proteins were established. Rapid Se-relayed CM was further investigated through biomimetic chemical access to Se-allyl selenocysteine (Seac) via dehydroalanine. On-protein reaction kinetics revealed rate constants of Seac-mediated CM to be comparable or superior to off-protein rates of many current bioconjugations. This CM strategy was applied to histone proteins to install a mimic of acetylated lysine (K9Ac, an epigenetic marker). The resulting synthetic H3 was successfully recognized by antibody that binds natural H3-K9Ac. A Cope-type selenoxide elimination subsequently allowed the removal of such modification to regenerate dehydroalanine. Finally, preliminary research efforts towards metabolic incorporation of allyl sulfide-containing amino acid into proteins, and CM on cell surfaces were discussed.
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Harmse, Liesel. "Improvement of propylene yield via butene metathesis." Master's thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/5323.
Full textAbstract:
Includes synopsis.Includes bibliographical references (leaves [96]-100).
There is an increasing interest in finding ways to produce on-purpose propene, due to the significant predicted propene growth in the next few years without the concomitant growth in the ethene demand, One of the technologies available is 1-butene metathesis, which describes a one-step process where isomerisation of 1-butene to 2-butene followed by cross-metathesis taking place. Products of the cross metathesis are propene and 2-pentene. In addition ethene and 3-hexene are expected as products of 1-butene metathesis.
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do, Nascimento Daniel Luis. "Olefin Metathesis Catalysts: From Decomposition to Redesign." Thesis, Université d'Ottawa / University of Ottawa, 2021. http://hdl.handle.net/10393/42541.
Full textAbstract:
Olefin metathesis is arguably the most versatile catalytic route yet developed for the assembly of carbon-carbon bonds. Metathesis methodologies are attractive from both synthetic and ecological standpoints, because they employ unactivated double bonds. This reduces the total number of synthetic steps, and the associated generation of chemical wastes. The drive to deploy olefin metathesis in highly demanding contexts, including pharmaceutical manufacturing and chemical biology, puts severe pressure on catalyst lifetime and productivity. Understanding the relevant decomposition pathways is critical to achieve essential performance goals, and to enable informed catalyst redesign. This thesis work expands on significant prior advances that identified and quantified critical decomposition pathways for ruthenium catalysts stabilized by N-heterocyclic carbene (NHC) ligands. Because pristine catalyst materials are essential for mechanistic study, it focuses first on methods aimed at improving efficiency and purity in catalyst synthesis. Merrifield iodide resins were shown to function as efficient, selective phosphine scavengers in the production of clean second-generation catalysts from PCy3- stabilized precursors.
The thesis then turns to mechanistic examination of decomposition pathways that underlie success and failure for leading NHC catalysts, for comparison with a new family of catalysts stabilized by cyclic (alkyl)(amino) carbene (CAAC) ligands. These represent the first in-depth mechanistic studies of the CAAC catalysts, which have attracted much attention for their breakthrough productivities in challenging metathesis reactions. The remarkable productivity of the CAAC catalysts is shown to originate in their resistance to decomposition of the key metallacyclobutane intermediate via b-elimination, and (to a lesser extent) in their resistance to attack by nucleophiles and Bronsted bases. Importantly, however, they are more susceptible to bimolecular decomposition. The latter behaviour, as well as their resistance to b-elimination, is traced to the strong trans influence of the CAACs relative to NHC ligands. This insight significantly advances our understanding of the fundamental properties governing both productivity and decomposition.
Finally, two new catalysts are developed, building on the principle that nucleophilic stabilizing ligands should be avoided in the precatalysts. In the first of these complexes, an o-dianiline ligand is employed to stabilize the precatalyst. This flexible, H-bonding chelate serves the further purpose of accelerating macrocyclization of flexible dienes that bear polar functionalities. As its H-bonding capacity also increases its sensitivity to trace water, however, an alternative catalyst architecture was pursued. The latter consists of a dimer bearing bulky Ru-indenylidene centers, in which a dative bond from a bridging chloride affords the fifth ligand essential to stabilize the precatalyst.
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Lu, Pengfei. "Aziridine-metathesis based approaches to alkaloid synthesis." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/4392.
Full textAbstract:
The aim of the project is to synthesise (–)-morphine utilising aziridine and metathesis chemistry. The thesis is divided into three chapters. Chapter 1 provides brief reviews on the subjects of total synthesis of morphine; ringrearrangement metathesis (RRM) and regioselective ring-opening of aziridines. Chapter 2 focuses on the research findings in the past three years. Two routes, A and B, were investigated in attempts to synthesise morphine (Scheme 1). In route A, sulfonyl cyclopentene II was prepared from ring-closing metathesis of a diene precursor, which was synthesised from lithiated cinnamylsulfone and butadiene monoxide. Subsequently, RRM reactions of several α-SO2Ph allyl derivatives of II were investigated and some interesting results were obtained. The synthesis of 2,3-trans vinylaziridine III was achieved in seven steps beginning with a Grignard reaction of (4- methoxyphenyl)magnesium bromide with butadiene monoxide. Subsequently, some highly regioselective ring-opening reactions of III with sulfur-stabilised anionic nucleophiles were achieved. However, in an attempt to synthesise compound I from II and III, no reaction was observed. This led to the investigation of route B, in which five methods for the synthesis of compound IV were investigated. The practical approach deployed a novel Al-mediated substitution of the 4-tosyl group of the tosyl tetrahydropyridine counterpart of IV, prepared from V and III, with a phenylthio group. Chapter 3 provides the experimental details and characterisation data.
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Nagano, Takashi. "Metathesis route to bridged metallocenes and phosphametallocenes." 京都大学 (Kyoto University), 2005. http://hdl.handle.net/2433/145117.
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Zimmerer, Julia [Verfasser]. "Olefin Metathesis of Microalgae Lipids / Julia Zimmerer." Konstanz : KOPS Universität Konstanz, 2020. http://d-nb.info/1220636932/34.
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Mann, Tyler J. "Stereoselective Olefin Metathesis Reactions Catalyzed by Molybdenum Monoaryloxide Monopyrrolide Complexes." Thesis, Boston College, 2016. http://hdl.handle.net/2345/bc-ir:104995.
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Thesis advisor: Amir H. HoveydaChapter 1: Efficient Z-Selective Cross-Metathesis of Secondary Allylic Ethers Efficient Z-selective cross-metathesis of secondary allylic ethers were catalyzed by monoaryloxide monopyrrolide molybdenum complexes. Reactions involving both silyl and benzyl protected ethers were demonstrated, as well as ethers containing alkyl, aryl and alkynyl substituents. Mechanistic studies were performed, and the reactions were applied to the total synthesis of several ene-diyne natural products. Chapter 2. Stereoselective Total Synthesis of Disorazole C1 The stereoselective total synthesis of disorazole C1 is reported. The synthesis was completed in 12 longest linear steps. Our synthesis demonstrates the utility of Z-selective cross-metathesis to form both alkenyl borons and alkenyl halides. Another key transformation was a one-pot Suzuki-dimerization reaction to form a symmetric 30 membered ring in relatively high yield. Chapter 3. Stereoselective Cross-Metathesis to Form Trisubstituted Alkenes Initial studies into the stereoselective formation of trisubstituted olefins through molybdenum catalyzed cross-metathesis have been performed. Our mechanistic understanding of the reaction lead us to focus on the synthesis of alkenyl halides, which can be obtained in up 90% yield and 75:25 E:Z selectivity. Chapter 4: Ring-Closing Metathesis in the Synthesis of Natural Products Development of highly efficient and selective ring-closing metathesis reactions have enabled collaborators to successfully implement routes in total synthesis endeavors. A diastereoselective seven-membered ring-closing metathesis enabled the successful synthesis of (±)-tetrapetalone A methyl-aglycon. An enantioselective ring-closing metathesis to form a six membered ring has provided access to enantioenriched aspidosperma alkaloids
Thesis (PhD) — Boston College, 2016
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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Hohn, Ida Marcia. "Kinetic studies of the metathesis of 1-hexene using Re2O7/γ-Al2O3, and the synthesis and metathesis of oxazolines." Thesis, Aston University, 1991. http://publications.aston.ac.uk/9797/.
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The kinetics of the metathesis of 1-hexene using Re2O7/-Al_2O_3 as the catalyst were investigated under a variety of conditions. The experiments were carried out under high vacuum conditions. The product solutions were characterised by gas liquid chromatography and mass spectroscopy. The initial kinetics of the metathesis of 1-hexene showed that the reaction was first order in the weight of the catalyst and second order in the concentration of 1-hexene. A kinetic scheme which correlated the experimental data with the metallocarbene chain mechanism postulated by Herisson and Chauvin and the kinetics of the reaction was explained using a model based on the Langmuir-Hinshelwood theory. The low conversion of 1-hexene to its products is due to termination reactions which most likely occur by the decomposition of the metallocyclobutane intermediate to produce a cyclopropane derivative and an inactive centre. The optimum temperature for the metathesis of 1-hexene over Re_2O_7/-Al2O3 is 45oC and above this temperature, the rate of metathesis decreases rapidly. Co-catalysts alter the active sites for metathesis so that the catalyst is more selective to the metathesis of 1-hexene. However, the regeneration of metathesis activity is much worse for promoted catalysts than for the unpromoted. The synthesis and metathesis of 4,4-dimethyl-2-allowbreak (9-decenyl)-1,3-oxazoline and 4,4-dimethyl-2-allowbreak (3-pentenyl)-1,3-oxazoline was attempted and the products were analysed by thin layer chromatography, infra-red, 13C and 1H nmr and mass spectroscopy. Obtaining the oxazolines in a good yield with high purity was difficult and consequently metathesis of the impure products did not occur.
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Steele, Rory G. "Synthesis of fused cyclic ethers : towards the synthesis of hemibrevetoxin B." Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363594.
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Ou, Xinrui. "Studies of Leading Catalysts for Olefin Metathesis: Evaluation of Synthetic Routes and Participation in Catalysis." Thesis, Université d'Ottawa / University of Ottawa, 2021. http://hdl.handle.net/10393/42777.
Full textAbstract:
Olefin metathesis is increasingly popular for the construction of carbon-carbon double bonds. In the past two decades, ruthenium metathesis catalysts have seen extensive development. Two marvelous early developments were the introduction of N-heterocyclic carbene (NHC) ligands, which greatly improved catalyst activity, and replacement of a nucleophilic stabilizing ligand (the alkylphosphine PCy3) by a chelated benzylidene-ether. A more recent breakthrough is the introduction of cyclic alkyl amino carbene (CAAC) ligands as alternatives to the NHCs. Over the past 5 years, the CAAC catalysts have drawn much attention for their breakthrough productivity in challenging reactions, including ethenolysis and RCM macrocyclization.
Nevertheless, important challenges remain. As discussed in the first part of this thesis, these include the synthesis of key ligands (in particular, the styrenyl ether ligands H2C=13CH-C6H4-2-OiPr and H2C=13CH-C6H3-2-OiPr-5-NO2), which represent the source of the chelated benzylidene-ether noted above) and key catalysts (e.g., Hoveyda- and Grela-class catalysts bearing an H2IMes or CAAC carbene ligand). A further challenge lies in understanding the behaviour of the styrenyl ether ligands – for example, how they contribute to catalyst partitioning between active, resting-state, and decomposed species, and the impact of the carbene ligand on that partitioning.
An initial objective was synthesis of labelled styrenyl ethers that would enable synthesis of Hoveyda and Grela catalysts with a 13C-label at the alkylidene carbon. While H2C=13CH-C6H4-2-OiPr could be accessed, its nitro analogue could not, probably owing to attack on the NO2 substituent. The remainder of Chapter 2 assessed reported routes to HII/nG and HII-C1/nG-C1, and reports on challenges and reproducibility issues. Difficulties in synthesis of the CAAC catalysts are attributed to the need for in situ-generated CAACs, and catalyst decomposition by the base required for deprotonation (i.e KHMDS or LiHMDS).
The second part of this thesis explores the impact of the NHC or CAAC ligands on initiation and “boomerang” recapture of the styrenyl ether ligands for Hoveyda- and Grela-class catalysts. Examination of the kinetics of initiation with bulky t-butyl vinyl ether (tBuVE) revealed a linear dependence of kobs on [tBuVE], and faster reaction by the p-NO2-substituted Grela catalyst. These data suggest an associative or interchange-associative (IA) mechanism. A systematic comparison of initiation rate constants revealed the trend HII > nG-C1 > HII-C1 in chlorinated and aromatic solvents. Recapture of added styrenyl ether ligand was examined in macrocyclization (mRCM). Rate plots indicated inhibition by this ligand, even at the high dilutions required for mRCM, implying that boomerang re-uptake of the styrenyl ether is indeed operative for both Hoveyda- and Grela-class catalysts. However, inhibition was found to be more profound for HII than HII-C1 or nG-C1. That is, the NHC catalysts are much more susceptible to partitioning into the off-cycle (precatalyst) form than are the CAAC catalysts. This higher commitment to the active cycle may be an important contributor to the impressive productivity of the CAAC catalysts. In addition, the slow initiation of these catalysts indicated above may be an asset, rather than a limitation, as it inhibits their susceptibility to bimolecular decomposition.
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Priebe, Joshua Michael. "Synthesis and enzymatic degradation of poly (ester amide) polymers made by acyclic diene metathesis." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0004408.
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McClennan, William. "Decomposition of Phosphine-Stabilized Metathesis Catalysts by Lewis Donors." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35593.
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Olefin metathesis has had tremendous impact on synthetic approaches to the formation of new carbon-carbon bonds. Heterogeneous metathesis catalysts have been used in industry for decades, to effect redistribution of olefin chain lengths in petrochemicals processing. Only recently, however, has olefin metathesis emerged in pharmaceutical and specialty chemical manufacturing. The nearly 20-year gap between the discovery of easily-handled ruthenium catalysts and industrial implementation in these sectors is a result of many factors. One key contributor is the limited understanding of decomposition mechanisms that limit the reliability of olefin metathesis. Poor catalyst selectivities and yields remain a challenge for industrial uptake of olefin metathesis. Much academic effort focuses on designing methods and new catalysts for catalyst separation and reuse. Exploration of catalyst decomposition pathways has seen much less study in comparison. The limited recognition of decomposition as a problem in academia is undoubtedly due to the tendency to use high catalyst loadings, which mask catalyst decomposition problems. The catalyst loadings commonly reported in academia need to be decreased by a factor of 100–1000 for industrial viability in many processes.
This thesis explores the decomposition of metathesis catalysts bearing a phosphine ligand. Such Grubbs-type catalysts, particularly second-generation versions containing an N-heterocyclic carbene ligand, are the most widely used metathesis catalysts in current use. This study follows up on an earlier discovery from the Fogg group, which showed that pyridine and amine donors drastically accelerate decomposition of the Grubbs catalysts. For the first-generation Grubbs catalyst, decomposition of the resting-state methylidene complex RuCl2(PCy3)2(=CH2) Ru-6 was shown to proceed via nucleophilic attack of PCy3 on the Ru=CH2 bond, forming a σ-alkyl complex that was intercepted and characterized crystallographically. Further reaction led to liberation of the methyl phosphonium salt [MePCy3]Cl 2. Under the same conditions, the second-generation methylidene complex Ru-4a decomposes rapidly without any detectable σ-alkyl intermediate. In this thesis, decomposition of the important second-generation catalysts is shown to proceed via the methylidene-abstraction pathway. These studies centered on the methylidene complex RuCl2(NHC)(PCy3)(=CH2), where the NHC ligand is H2IMes (Ru- 4a) or IMes (Ru-4b). The short lifetime of the σ-alkyl complex was tentatively attributed to the ease of activation of a C–H bond on the NHC ligand (specifically, those on the mesityl o-methyl group). This intermediate could not be observed for Ru-4a, but could be observed for the IMes system Ru-4b. This is suggested to reflect the slower rotation of the H2IMes ligand about the Ru–NHC bond, which promotes C–H activation.
Also examined is the ability of other Lewis donors to trigger this methylidene abstraction pathway during catalysis. Lewis donors are shown to greatly accelerate decomposition of a wide range of phosphine-stabilized metathesis catalysts. Remarkably, even weak donors such as water, ethers, alcohols, and nitriles (i.e. functionalities that are widespread among contaminants, functional groups, and “green solvents”) are shown to promote this pathway. Phosphine-stabilized catalysts are generally regarded as more robust towards such donor functionalities, and the detrimental impact of such weak donors has gone widely unrecognized. These findings have profound implications for catalyst choice and use.
Finally, a deuterium-labelling study was undertaken, in which the mesityl substituents on the NHC ligand were fully deuterated, to confirm that the proton in the phosphonium salt 2 indeed originates in the mesityl methyl group. Of note, the energies of the PCy3 dissociation and C–H activation steps were found to be closely similar. This was unexpected, given prior evidence that PCy3 loss is rate-determining in the Ru-2 precatalysts, and the much stronger Ru–PCy3 bonding known to be present in the methylidene complexes. This finding highlights the need to impede C-H activation for phosphine-stabilized metathesis catalysts. More broadly, it underscores the risks inherent in the use of phosphine-stabilized catalysts, or indeed of catalysts that are stabilized by a donor group that can function as both a Lewis base, and a nucleophile.
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Yu, Miao. "Stereoselective Olefin Metathesis Reactions for Natural Product Synthesis." Thesis, Boston College, 2014. http://hdl.handle.net/2345/3861.
Full textAbstract:
Thesis advisor: Amir H. HoveydaChapter 1. The first examples of highly Z- and enantioselective ring-opening/cross-metathesis reactions are disclosed. Transformations involve meso cyclic olefin substrate and styrenes or enol ethers as olefin cross partners. A stereogenic-at-Mo monoaryloxide monopyrrolide (MAP) complex, prepared and used in situ, is discovered for the efficient formation of Z olefins. Such complex, bearing a relatively smaller adamantylimido and a larger chiral aryloxide ligand, leads to kinetic Z-selectivity due to the size differential. In most cases, the resulting disubstituted Z olefins are formed with excellent stereoselectivity (>95% Z). Chapter 2. The protocols for efficient Z-selective formation of macrocyclic disubstituted alkenes through catalytic ring-closing metathesis (RCM) is described. Stereoselective cyclizations are performed with either Mo- or W-based monoaryloxide monopyrrolide (MAP) complex at 22 oC. Synthetic utility of such broadly applicable transformation is demonstrated by synthesis of several macrocyclic natural products: relatively simpler molecules such as epilachnene (91% Z) and ambrettolide (91% Z), as well as advanced precursors to epothilones C and A (97% Z) and nakadomarin A (94% Z). Several principles of catalytic stereoselective olefin metathesis reactions are summarized based on the studies: 1) Mo-based catalysts are capable of delivering high activity but can be more prone to post-RCM isomerization. 2) W-based catalysts, though furnish lower activity, are less likely to cause the loss of kinetic Z selectivity by isomerization. 3) Reaction time is critical for retaining the stereoselectivity gained from kinetic, which not only applicable with MAP complexes but potentially with other complexes as well. 4) By using W-based catalyst, polycyclic alkenes can be accessed with sequential RCM reactions, without significant erosion of the existing Z olefins in the molecule. Chapter 3. An enantioselective total synthesis of anti-proliferative agent (+)-neopeltolide is presented. The total synthesis is accomplished in 11 steps for the longest linear sequence and 28 steps in total, including 8 catalytic reactions. Particularly, several Mo- or Ru-catalyzed stereoselective olefin metathesis reactions as well as N-hetereocyclic carbene (NHC)-catalyzed enantioselective boron conjugate addition to an acyclic enoate have proven to be effective for convergent construction of the molecule. The most important novelty of the study incorporates the explorations of feasibility of Z-selective cross-metathesis reactions to solve the challenge of installing two Z olefins with excellent selectivity
Thesis (PhD) — Boston College, 2014
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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Hastings, Jedidiah M. "Olefin metathesis in supramolecular and ring-opening polymerization." [Gainesville, Fla.] : University of Florida, 2006. http://purl.fcla.edu/fcla/etd/UFE0015602.
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Amoroso, Dino. "New concepts in design of olefin metathesis catalysts." Thesis, University of Ottawa (Canada), 2002. http://hdl.handle.net/10393/6317.
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Treatment of compounds with general formula RuCl2(PP)(PPh 3) (PP = dppb (3a); binap (3b); dcypb ( 3c)) or [RuCl2(PP)]2 (PP = dppb (4); dcypb (5)) with PhCHN2 generates alkylidene complexes of the type RuCl2(PP)(CHPh) (2a--c), the first such systems to exhibit high ROMP activity without halide or phosphine abstraction. Low polymer polydispersity is found in ring-opening metathesis polymerization (ROMP) of norbornene via these catalysts. Investigations into the role of dissociated PPh3 show that free phosphine acts as a poison, dramatically retarding the rate of polymerization via 3 relative to catalysts derived from 4 or 5. Chelate retention is suggested by the narrow polydispersities and increased cis olefin content of the polymers obtained, and is consistent with the detrimental effects of phosphine scavenger. Reaction of RuCl2(PPh3)3 with bis(dicyclohexyl)-1,4-phosphinobutane (dcypb) under N2 gives access to PPh3-free RuCl(dcypb)(mu-Cl) 3Ru(dcypb)(N2) 5 in which the presence of N 2 and dative chloride bridges stabilize two equivalents of "RuCl 2(dcypb)". Under Ar or vacuum atmosphere, decomposition occurs via Ru-promoted dehydrogenation of the dcypb ligand, while reaction with chlorinated solvents rapidly yields paramagnetic RuCl(dcypb)(mu-Cl)3RuCl(dcypb) 6. However, the N2-stabilized species 5 is easily handled under N2 in non-chlorinated solvents, giving an ideal entry point into Ru-dcypb chemistry. The N2 ligand within 5 is readily displaced under H2 or CO atmosphere, yielding RuCl(dcypb)(mu-Cl)3Ru(dcypb)(H2) 6 or RuCl2(dcypb)(CO)2, the latter as a mixture of ccc (8) and tcc (9) isomers. Interestingly, the CO ligands can be displaced, and the symmetrical dimer RuCl(dcypb)(CO)(mu-Cl)2RuCl(dcypb)(CO) 10 is formed by decarbonylation of 8/9 on prolonged storage under N2. The incorporation of the stable silylene ligand 1,3-di-tert-butyl-1,3,2-diazasilol-2-ylidene (SiLN2) in to the ligand scaffold of a metathesis catalyst was undertaken to probe its utility as a phosphine mimic. Reaction of [(dcypb)ClRu(mu-Cl)3Ru(dcypb)(N2)] (5) with 4 equivalents of the silylene yields coordinatively unsaturated RuCl(eta 3-dcypb)(SiLN2) (12). Complex 12 is a rare example of a trans-spanning diphosphine complex, this geometry resulting from an unprecedented attack of the metal on the tetramethylene ligand backbone. (Abstract shortened by UMI.)
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Barker, William D. "Photoannulation and ring closing metathesis of carbohydrate derivatives." Thesis, University of Leicester, 2000. http://hdl.handle.net/2381/30040.
Full textAbstract:
The 'chiron approach' is a well-recognised technique for converting carbohydrates and other naturally occurring compounds into new chiral target molecules. The success of this area of chemistry can be attributed to the vast array of novel methods for transforming carbohydrates that have been developed over the last 50 years. Chapter 1 describes some of the key discoveries and pioneers within the field of carbohydrate annulation. As part of the Jenkins groups' on-going studies into the development of new methods for carbohydrate annulation, we have demonstrated the ease in which simple carbohydrate derivatives can be cyclised by Ring Closing Metathesis (RCM). Using Grubbs ruthenium catalyst 176b, we have cyclised a range of substrates derived from D-glucose to give annulated products such as 307. Some of the adducts have been reduced by well known methodology to give chiral fragments such as 348 which may be used as 'chiron' in further synthesis (Chapter 2). (Fig. 10916A). We have also utilised the copper (I) triflate catalysed intramolecular [2+2] photocycloaddition reaction to cyclise a range of carbohydrate derivatives such as 306 to afford enantiomerically pure products 400 and this represents a novel method to add to the increasingly wide range of techniques for annulating carbohydrates. (Fig. 10916B). To further extend the scope of the catalysed [2+2] photochemical ring closure reaction, we have investigated a variety of reagents in an attempt to make it an asymmetric catalytic process. The chiral diene 535 can be cyclised in the presence of a number of chiral catalysts such as 554 to give two enantiomeric tricyclic products 536a and 536b, which can be quantitatively analysed by chiral hplc. The chiral catalyst should favour on enantiomer over the other. We have considered a variety of substrates, reagents and reaction conditions, and the results are reported in chapter 4. (Fig. 10916C).