Download or read book Ruthenium based Olefin Metathesis Catalysts Bearing PH responsive Ligands written by Shawna Lynn Balof and published by . This book was released on 2011 with total page 306 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Design and Synthesis of Ruthenium Indenylidene based Catalysts for Olefin Metathesis written by César A. Urbina-Blanco and published by . This book was released on 2013 with total page 183 pages. Available in PDF, EPUB and Kindle. Book excerpt: As part of a European wide effort to develop metathesis catalysts for use in fine chemical and pharmaceutical compound synthesis, this study focuses on the design and synthesis of ruthenium based catalysts for olefin metathesis. The aim, of this work was simple: to develop new, more active, more stable, easy to synthesise and commercially viable Ruthenium based catalysts, as well trying to rationalize the effect of structural changes on reactivity. Two different approaches were explored in order to develop more active catalysts bearing N-heterocyclic carbene (NHC) ligands: changing the leaving group and the effect of the NHC moiety in indenylidene type complexes. Over 12 new catalysts were developed and their activity compared to that of commercially available catalysts. Overall, the new complexes exhibited superior reactivity compared to previously reported catalysts in several benchmark transformations. However, olefin metathesis is a very substrate specific reaction, and rather than finding one catalyst that is superior to all, a catalogue of catalysts suitable for specific transformations was developed. In addition, the effect of structural changes on substrate activity was investigated in the ring closing metathesis of 1,8-nonadienes. The reaction profiling showcased the presence of a gem-difluoro group as an accelerating group in this incarnation of the olefin metathesis reaction and leads to ring formation over polymerization. In order to rationalize the effect of structural changes on catalyst activity, kinetic studies dealing with the initiation mechanism of ruthenium-indenylidene complexes were examined and compared with that of benzylidene counterparts. It was discovered that not all indenylidene complexes followed the same mechanism, highlighting the importance of steric and electronic properties of so-called spectator ligands, and that there is no single mechanism for the ruthenium-based olefin metathesis reaction. These results highlight the importance of systematic development of catalysts and that as scientists we should not take for granted.

Download or read book Longer lived Olefin Metathesis Catalysts Based on Molybdenum and Ruthenium written by Joseph Yoon and published by . This book was released on 2020 with total page 91 pages. Available in PDF, EPUB and Kindle. Book excerpt: The field of olefin metathesis has seen considerable growth in the recent past. Some of the earliest milestones in the field include the synthesis of well-defined catalysts based on molybdenum, tungsten, and ruthenium. The efficiencies of these catalysts, however, are limited by their decomposition. Efforts have been made to increase the lifetime of these catalysts by changing the ligand sphere, to stabilize catalytic intermediates. Examples include the employment of the N-heterocyclic carbene (NHC) and the chelating (o-isopropoxy)benzylidene ligand seen in the second-generation Grubbs and Hoveyda catalysts. Processes that utilize the olefin metathesis processes, like those in the petroleum industry and large-scale production of chemicals, are bound by the need for high catalyst loadings which translate to high costs. The work herein presents the pursuit of longer-lived olefin metathesis catalysts based on molybdenum and ruthenium. The first goal of this thesis project was to develop a stable molybdenum-based olefin metathesis catalyst supported by a tridentate PONOP ligand and a chelating (o- x methoxy)benzylidene ligand. Previous attempts in our lab employed nonchelating alkylidene initiators - yielding no success in isolation. The rationale behind this design was that a chelating ether moiety will stabilize the molybdenum-center enough to be isolable. Attempts to isolate the chelating molybdenum-alkylidene species were also unsuccessful. Instead, we probed the in-situ ROMP of norbornene using iPrPONOP MoCl3 as a precatalyst and (2-methoxybenzyl)magnesium chloride as a cocatalyst. This cocatalyst did not lend any improvements to the simpler nonchelating Grignard cocatalysts. The synthesis of a novel dialkyl zirconocene complex is also reported. The second and more heavily pursued endeavor was the development of longer-lived ruthenium olefin metathesis catalysts. Specifically, we aimed at improving the second-generation Hoveyda catalyst with the use of a hemilabile tridentate NHC ligand. Two novel catalysts bearing NHC ligands with a hemilabile ethoxy-pyridyl arm were synthesized along with their unique organic frameworks. The catalyst containing the 2,6-diisopropylphenyl group (C1-Me) was investigated more comprehensively because it was more readily prepared. This complex was characterized by high thermal stability under metathesis conditions and remarkable TONs in the self-metathesis of 1-decene. In our efforts to prepare C1-Me without utilizing a Grubbs I intermediate, a new complex (6) bearing our NHC ligand was isolated and characterized by 1H NMR and single crystal x-ray diffraction spectroscopy. The reaction of C1-Me with ethylene did not produce the desired C1-Me-methylidene variant - however, the same reaction with propylene gave C1-Me-ethylidene with relative ease. Analyzing the active catalytic species under the metathesis of 1-decene revealed that the resting state of the catalyst is not the expected methylidene, but rather the longer chain nonylidene. xi Initiation studies were conducted to compare the rates of initiation for catalyst C1-Me and the nonmethylated C1-H. First, the rate of metathesis was followed in the irreversible reaction with ethyl vinyl ether. Second, ligand exchange equilibrium experiments were carried out to compare the dissociation constants for the pyridyl moieties in both catalysts. The outcome of these studies revealed that catalyst C1-Me, with a methyl group in the phenoxide ring, exhibits a 10-fold increase in initiation versus the nonmethylated C1-H catalyst. The NHC ligand scaffold reported in this work may assist in the development of other inorganic and organometallic catalytic systems, as many rely on the use of ancillary ligands for support. Furthermore, fixing a hemilabile ethoxy-pyridyl arm onto already robust systems, such as ruthenium catalysts bearing a cyclic alkyl amino carbene ligand, may offer even greater catalytic turnover numbers (TONs).

Download or read book Green Metathesis Chemistry written by Valerian Dragutan and published by Springer Science & Business Media. This book was released on 2009-10-26 with total page 432 pages. Available in PDF, EPUB and Kindle. Book excerpt: An outstanding international scientific event in the field of metathesis chemistry, the NATO ASI "Green Metathesis Chemistry: Great Challenges in Synthesis, Catalysis and Nanotechnology" has been recently organized in Bucharest, Romania (July 21- August 2, 2008). Numerous renowned scientists, young researchers and students, convened for two weeks to present and debate on the newest trends in alkene metathesis and identify future perspectives in this fascinating area of organic, organometallic, catalysis and polymer chemistry with foreseen important applications in materials science and technology. Following the fruitful practice of NATO Advanced Study Institutes, selected contributions covering plenary lectures, short communications and posters have been compiled in this special volume dedicated to this successful convention on green metathesis chemistry. General interest was primarily focused on relevant "green chemistry" features related to all types of metathesis reactions (RCM, CM, enyne metathesis, ADMET and ROMP). Diverse opportunities for green and sustainable technologies and industrial procedures based on metahesis have been identified. Largely exemplified was the utility of this broadly applicable strategy in organic synthesis, for accessing natural products and pharmaceuticals, and also its ability to fit in the manufacture of smart and nanostructured materials, self-assemblies with nanoscale morphologies, macromolecular engineering.

Download or read book Novel Olefin Metathesis Catalysts Bearing a Hemi labile NHC Ligand written by Nicolas Cena and published by . This book was released on 2019 with total page 79 pages. Available in PDF, EPUB and Kindle. Book excerpt: The field of olefin metathesis has grown appreciatively in recent decades. Elucidation of the mechanism and a deeper understanding of the key intermediates have enabled chemists to design catalysts, which exhibit greater activity, stability, and selectivity towards a variety of substrates. However, the economic impact of performing this reaction on the industrial scale is often governed by the high cost of the catalysts in comparison to modest turnover numbers (TON). The lifetime of an active catalyst species depends on the stability of intermediates in the catalytic cycle, and this ultimately determines the TON. One of the remaining goals in the field is to further stabilize the intermediates of the catalytic cycle in order to prolong the catalyst lifetimes and increase turnover numbers (TON). The ruthenium catalytic species cycle through several electron deficient intermediates, which lead towards decomposition pathways. These decomposition pathways are directed towards reactions that provide the metal with additional electron density. The primary focus of this thesis project was to develop a new generation of olefin metathesis catalysts employing a tridentate N-heterocyclic carbene (NHC) ligand bearing a hemi labile pyridine arm in the ortho position of the aromatic ring. The rationale behind incorporating these functional groups was to stabilize the reactive intermediates of the catalytic cycle via electron donation from the ether O → Ru and the pyridine N → Ru. These ligands increase the likelihood of stabilization of the metal center by chelation of electron-donating substituents from the O and N, thus adding electron density back into the electron-deficient metal center. The ligand not only donates electron density back to the metal but also shields the sterically open position trans to the NHC. The hypothesis was that stabilizing these reactive intermediates would prolong the lifetime of the active catalyst and thus increase TON and allow for a much lower catalyst loading for industrial applications, thus vastly impacting the economical aspect of olefin metathesis processes. A novel set of two catalysts bearing tridentate NHC ligands with hemi labile pyridine arms were synthesized. The ligands differed in one aromatic ring containing either a 2,6 diisopropyl phenyl (DIPP) or mesityl (Mes) moiety. The result of the x-ray crystallographic analysis revealed the NHC ligand coordinated in the proposed tridentate meridional fashion around the central Ru atom. This coordination was proposed in order to affect a hinge-like mechanism in which the pyridine arm's hemi-labile nature would be in close proximity to the electron deficient metal center, so that it could bind reversibly in order to satiate the metal's desire for electron density while still allowing reactivity upon dissociation. NMR spectroscopy revealed information about the proposed structure in solution and revealed that the ligand was bound in solution to the metal center in one orientation, owing to the coordination of the O and N to the metal center. Catalyst decomposition studies were performed using the methylidene variant of the catalysts at elevated temperatures under inert conditions as well as under an atmosphere of ethylene gas. The purpose of intentionally decomposing the catalyst was to generate the electron deficient Ru center and probe the stabilizing effects of the pyridine arm coordination. These reactive intermediates are electronically and sterically more similar to the 14-electron active catalyst than the 16-electron pre-catalyst, giving insight into how the catalysts behave in solution upon metathesis active conditions. Decomposition products of the DIPP variant were analyzed by NMR and x-ray crystallography, giving insight into possible decomposition pathways for these novel catalysts. The catalysts were screened for metathesis activity in ring-closing metathesis (RCM) and ring opening metathesis polymerization (ROMP). Both showed noticeable differences from previous generations of Grubbs and Hoveyda-Grubbs catalysts in overall efficacy. The prolonged lifetimes of these new catalysts were competitive with commercially available catalysts in terms of lifetime and TON. Though slightly lower in TON, these catalysts lasted much longer in solution at elevated temperatures than their predecessors, thus indicating much more stabilized reactive intermediates. The data gathered from decomposition studies and metathesis activity along with NMR and x-ray crystallography allowed for potential structure-activity relationships and mechanistic pathways to be proposed. The insight into olefin metathesis catalyst structure, performance, and design provided by these studies may assist in future endeavors in the field of olefin metathesis catalyst design and employment.

Download or read book Ruthenium based Olefin Metathesis Catalysts Coordinated with N heterocyclic Carbene Ligands written by John Philip Morgan and published by . This book was released on 2003 with total page 296 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Efficient New Routes to Leading Ruthenium Catalysts and Studies of Bimolecular Loss of Alkylidene written by Craig Day and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Lewis Acid Activated Olefin Metathesis Catalysts written by Adam McKinty and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Ligand Design in Metal Chemistry written by Mark Stradiotto and published by John Wiley & Sons. This book was released on 2016-10-17 with total page 463 pages. Available in PDF, EPUB and Kindle. Book excerpt: The design of ancillary ligands used to modify the structural and reactivity properties of metal complexes has evolved into a rapidly expanding sub-discipline in inorganic and organometallic chemistry. Ancillary ligand design has figured directly in the discovery of new bonding motifs and stoichiometric reactivity, as well as in the development of new catalytic protocols that have had widespread positive impact on chemical synthesis on benchtop and industrial scales. Ligand Design in Metal Chemistry presents a collection of cutting-edge contributions from leaders in the field of ligand design, encompassing a broad spectrum of ancillary ligand classes and reactivity applications. Topics covered include: Key concepts in ligand design Redox non-innocent ligands Ligands for selective alkene metathesis Ligands in cross-coupling Ligand design in polymerization Ligand design in modern lanthanide chemistry Cooperative metal-ligand reactivity P,N Ligands for enantioselective hydrogenation Spiro-cyclic ligands in asymmetric catalysis This book will be a valuable reference for academic researchers and industry practitioners working in the field of ligand design, as well as those who work in the many areas in which the impact of ancillary ligand design has proven significant, for example synthetic organic chemistry, catalysis, medicinal chemistry, polymer science and materials chemistry.

Download or read book Electronic Structure Studies of Ruthenium based Catalysts for Olefin Metathesis written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Interest in olefin metathesis has increased over the years with the development of ruthenium-based catalysts. Their unique properties have allowed their use in numerous industrial and laboratory processes in relatively mild conditions and in combination with a wide range of solvents. Several studies have provided insights into how these catalysts work, but very little has been done in order to understand why they work that way; an important aspect that has the potential of benefiting chemists while designing new catalysts. The research introduced here has focused on the fundamental understanding of their reactivity by exploring their electronic structure, using a combination of synchrotron-based X-ray-absorption (XAS) techniques in combination with DFT calculations and multiplet simulations. As part of the experimental work, samples from various ruthenium-based catalysts classified as first-generation (whenever the ancillary ligand is a phosphine) or as second-generation analogues (whenever this ligand is an N-heterocyclic carbene, NHC) were used. The Ru K-edge XAS data have revealed that the ruthenium centre in second-generation analogues is more positively charged than the corresponding first-generation counterparts. This offers a rationale for previously observed kinetic results, which have shown a slower initial step for the second-generation Grubbs catalyst. At the same time, they raise questions in a more fundamental level on whether or not NHCs are truly better charge donors than phosphine ligands. DFT results are consistent and the ongoing analyses of the Cl K- and C K-edge XAS data indicate similar overall bonding structures between first- and second- generation analogues. In addition, from preliminary results on these edges, two possible identities of substantially different nature have emerged for the LUMO orbital. In this regard, the final conclusion should provide important insights on through which orbital the metathesis reaction gets started. As a sid.

Download or read book Ruthenium in Organic Synthesis written by Shun-Ichi Murahashi and published by John Wiley & Sons. This book was released on 2006-03-06 with total page 398 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this comprehensive book, one of the leading experts, Shun-Ichi Murahashi, presents all the important facets of modern synthetic chemistry using Ruthenium, ranging from hydrogenation to metathesis. In 14 contributions, written by an international authorship, readers will find all the information they need about this fascinating and extraordinary chemistry. The result is a high quality information source and a indispensable reading for everyone working in organometallic chemistry. From the contents: Introduction (S.-I. Murahashi) Hydrogenation and Transfer Hydrogenation (M. Kitamura and R. Noyori) Oxidations (S.-I. Murahashi and N. Komiya) Carbon-Carbon Bond Formations via Ruthenacycle Intermediates (K. Itoh) Carbon-Carbon Bond Formation via pi-Allylruthenium Intermediates (T. Mitsudo) Olefin Metathesis (R. H. Grubbs) Cyclopropanation (H. Nishiyama) Nucleophilic Addition to Alkynes and Reactions via Vinylidene Intermediates (P. Dixneuf) Reactions via C-H Activation (N. Chatani) Lewis Acid Reactions (E. P. Kundig) Reactions with CO and CO2 (T. Mitsudo) Isomerization of Organic Substrates Catalyzed by Ruthenium Complexes (H. Suzuki) Radical Reactions (H. Nagashima) Bond Cleavage Reactions (S. Komiya)

Download or read book Expanding the Scope of Ruthenium based Olefin Metathesis Catalysts written by Matthias Scholl and published by . This book was released on 2000 with total page 258 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Ruthenium based Olefin Metathesis Catalysts written by Eric Lee Kuiokalani Dias and published by . This book was released on 1998 with total page 113 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Novel Metathesis Chemistry Well Defined Initiator Systems for Specialty Chemical Synthesis Tailored Polymers and Advanced Material Applications written by Y. Imamoglu and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 355 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive discussion of the theory, practice and application of catalytically active transition metal species and their application in the production of specialist polymeric materials. The material is presented in a progressive manner, suitable for non-experts and those seeking an introduction to the field. The bibliographies supplied are complete and up to date, making the book an indispensable guide to the primary literature for the more theoretical background to the topics discussed. After a comprehensive discussion of initiating systems for speciality chemical synthesis the book goes on to deal with a wide range of topics in materials science, including: alkenamers, polyacetylenes, industrial applications and liquid rocket engine fuels.

Download or read book Hydroformylation for Organic Synthesis written by Maurizio Taddei and published by Springer. This book was released on 2014-07-08 with total page 233 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Role of Metals and Ligands in Organic Hydroformylation, by Luca Gonsalvi, Antonella Guerriero, Eric Monflier, Frédéric Hapiot, Maurizio Peruzzini. Hydroformylation in Aqueous Biphasic Media Assisted by Molecular Receptors, by Frédéric Hapiot, Hervé Bricout, Sébastien Tilloy, Eric Monflier. Asymmetric Hydroformylation, by Bernabé F. Perandones, Cyril Godard, Carmen Claver. Domino Reactions Triggered by Hydroformylation, by Elena Petricci, Elena Cini. Rhodium-Catalyzed Hydroformylation in Fused Azapolycycles Synthesis, by Roberta Settambolo. Hydroformylation in Natural Product Synthesis, by Roderick W. Bates, Sivarajan Kasinathan.

Download or read book Principles and Applications of Organotransition Metal Chemistry written by James Paddock Collman and published by . This book was released on 1987 with total page 1016 pages. Available in PDF, EPUB and Kindle. Book excerpt: This textbook introduces students and experienced chemists to a rapidly growing interdisciplinary subject. It incorporates a thorough revision of the earlier edition, and includes all new developments.

Download or read book Rhenium based Olefin Metathesis Catalysts and Investigation of Ligand Properties written by Yu-Ying Lai and published by . This book was released on 2011 with total page 165 pages. Available in PDF, EPUB and Kindle. Book excerpt: