Investigations into the Selectivity of Olefin Cross-Metathesis Using Ruthenium Alkylidene. Catalysts Electronic and Steric Matching of Substrates. Thesis by. Arnab Kumar Chatterjee. In Partial Fulfillment of the Requirements for the degree of. Doctor of Philosophy. CALIFORNIA INSTITUTE OF TECHNOLOGY. Pasadena. Ring-opening metathesis polymerization (ROMP) uses metathesis catalysts to generate polymers from cyclic olefins. ROMP is most effective on strained cyclic olefins, because the relief of ring strain is a major driving force for the reaction – cyclooctene and norbornenes are excellent monomers for ROMP, but cyclohexene is very reluctant to form any significant amount of polymer. Norbornenes are favorite monomers for ROMP, as a wide range of monomer functionalities are easily available through Diels-Alder reactions. Careful balance of catalyst, monomer, and other factors can offer excellent control of the polymer structure. In terms of homogeneous catalysts, most tungsten and molybdenum catalysts (Schrock catalysts) have rapid initiation rates and can produce “living” polymerizations with excellent control of polydispersity and chain tacticity, but the low functional group tolerance limits the monomers available. Commercial Applications of Ruthenium Olefin Metathesis Catalysts in Polymer Synthesis. Ruthenium metathesis catalysts (Grubbs catalysts) tend to have slower initiation rates, often leading to higher polydispersities, but their air stability and greater tolerance for functional groups makes them “user friendly” and enables use of a wide range of functional monomers and additives. Secondary metathesis reactions (controlled by catalyst choice and reaction conditions) also affect the product distribution. Recoordination of an alkene on the growing polymer chain with the catalyst can lead to cyclic oligomers through a ring-closing metathesis reaction (“backbiting”).
Olefin metathesis is an organic reaction that entails the redistribution of fragments of alkenes olefins by the scission and regeneration of carbon-carbon double bonds. Catalysts for this reaction have evolved rapidly for the past few decades. Because of the relative simplicity of olefin metathesis it often creates fewer undesired by-products and hazardous wastes than alternate organic reactions. Because of their elucidation of the reaction mechanism and their discovery of a variety of highly efficient and selective catalysts, Yves Chauvin, Robert H. Schrock were collectively awarded the 2005 Nobel Prize in Chemistry.. The traditional, industrial catalysts are ill-defined and used mainly for Petroleum products. Modern catalysts are well-defined organometallic compounds that come in two main categories, commonly known as Schrock catalysts and Grubbs' catalysts. Schrock catalysts are molybdenum(VI)- and tungsten(VI)-based, and are examples of Schrock alkylidenes. Olefin metathesis was first commercialized in petroleum reformation for the synthesis of higher olefins from the products (alpha-olefins) from the Shell higher olefin process (SHOP) under high pressure and high temperatures. Modern catalysts can be used for a variety of specialized organic compounds and monomers.
In recent years, olefin cross metathesis CM has emerged as a powerful and convenient synthetic technique in organic chemistry; however, as a general synthetic. Ring-closing metathesis is a variant of the olefin metathesis reaction in which alkylidene moieties are exchanged to form a ring. The most common catalysts for this reaction are complexes of molybdenum or ruthenium. Olefin metathesis involves the exchange of two alkylidene groups to generate two new olefins from one or more starting alkenes. Cleavage of the carbon-carbon double bond is accompanied by the formation of two new carbon-carbon double bonds. This reaction was first observed in 1931, investigated by Du Pont and other manufacturers in the 1950's, Partly due to its relevance to petrochemical industry, olefin metathesis reactions have been investigated extensively. Although initial examples of ring-closing metathesis used poorly defined metal catalysts, subsequent development of Schrock-type molybdenum catalysts such as 1 and Grubbs-type ruthenium catalysts such as 2 - 6 greatly expanded the scope and utility of RCM (Eq. In general, molybdenum catalysts display high activity but are unstable toward air or water; ruthenium catalysts are less active but exhibit good selectivity and functional-group compatibility. Four general classes of reactions have emerged: cross metathesis, an intermolecular reaction of two alkenes; ring-opening metathesis polymerization (ROMP), in which a cyclic alkene opens to form a polyolefin; ring-opening metathesis (ROM), the opening of a cyclic alkene to form a diene; and ring-closing metathesis (RCM), in which reaction of a diene affords a cyclic alkene and a small olefinic byproduct. RCM has been employed extensively in organic synthesis to establish both saturated and unsaturated rings; the reaction can be used to form carbocycles or heterocycles. In RCM reactions, cycloaddition of one alkene with the catalyst affords metallacyclobutane intermediate 7 containing a pendant olefin. In a cycloreversion step, a small olefin is expelled and new metal carbene intermediate 8 forms, which still contains a tethered alkene.
Olefin cross-metathesis1 can be formally described as the intermolecular mutual exchange of alkylidene or carbene fragments between two olefins promoted by metal-carbene complexes. There are three main variations on this theme. Figure 1 a cross-metathesis, b ring-opening cross-metath- esis, and c. Xi Mo has developed a new process to encapsulate various molybdenum or tungsten based metathesis catalysts in paraffin, enabling all organic chemists to perform Mo/W based olefin metathesis on the bench, and eliminating the need for a glove-box. Read more New catalysts that facilitate the synthesis of di- or trisubstituted Z- or E-alkenes have found broad application in the synthesis of complex natural products as well as biologically active small molecules. Read more In situ methylene capping: A general strategy for efficient stereoretentive catalytic olefin metathesis is developed using Ru dithiolate catalysts. The concept, methodological implications, and applications to synthesis of biologically active compounds is described.
Why Cross Metathesis not used •Low catalyst activity to effect a reaction without an enthalipic driving force ring strain –Newer catalysts have been developed Ruthenium-Based Metathesis Catalysts Introduction Olefin metathesis is now a well-entrenched synthetic technique, and is a powerful method for the clean construction of innumerable classes of chemical architectures. Late-transition metal alkylidene complexes, specifically ruthenium alkylidenes, have propelled this synthetic methodology in to the forefront of carbon–carbon bond forming techniques in large part because of the functional group tolerance of these catalysts, and their ability to be handled without the use of glove box or Schlenk techniques. The broadly accepted belief that this key method transformed the landscape of synthetic chemistry ultimately led to the awarding of the 2005 Nobel Prize in Chemistry to the pioneers in olefin metathesis: Yves Chauvin, Robert H. As shown below, ruthenium alkylidenes participate in a host of reaction paradigms, all under the umbrella of olefin metathesis. Development of the second-generation catalysts and the Hoveyda–Grubbs modified catalysts were largely spurred by the need for more active catalysts that could effect transformations that the first-generation systems could not, such as the metathesis of sterically demanding and electron-poor olefins. While these improved catalysts broadened the realm of olefin metathesis reaction, there are instances where the first-generation catalysts continue to provide excellent or superior results in a given metathesis reaction. Thus, it is clear that in many cases, there is not a universal metathesis catalyst. Sigma-Aldrich is proud to be the exclusive research scale supplier of Materia’s ruthenium metathesis catalysts, including first- and second-generation Grubbs and Hoveyda–Grubbs catalysts. We have recently expanded our portfolio to include five state-of-the-art catalysts, with unique reactivities and tailored initiation rates. These “next-generation” catalysts expand the scope of this powerful reaction class, allowing for example, metathesis reactions to be performed at low temperatures, and for the formation of tetrasubstituted olefins via cross metathesis. Advantages generation catalyst, thus useful in highly exothermic ROMP applications.
In recent years, olefin cross metathesis CM has emerged as a powerful and convenient synthetic technique in organic chemistry; however, as a general synthetic method, CM has been limited by the lack of predictability in product selectivity and stereoselectivity. Investigations into olefin cross metathesis with several. D Processes as Quantified by E Factors XPhos may be used as a ligand in the following reactions:• Preparation of functionalized benzylic sulfones via palladium-catalyzed Negishi cross-coupling between alkyl sulfones and aryl halides. 1, 5, 25, 100, 500 g in glass bottle Usage subject to US Patent 7,223,879 Usage subject to US Patents 63070916. Sigma Life Science is committed to bringing you Greener Alternative Products, which adhere to one or more of The 12 Principles of Greener Chemistry. This product has been enhanced for energy efficiency. XPhos [2-Dicyclohexylphosphino- Buchwald Phosphine Ligands - Technical Article Over the past several years, the Buchwald group has developed a series of bulky electron-rich phosphines that have garnered much attention for their ability to effect various C–C, C–N, and C–O bond f... Keywords: Aldrichimica Acta, Arylations, C-X bond formation, Catalysis, Chemfiles, Coupling reactions, Ligands, Methods, Type Buchwald Phosphine Ligands Sigma-Aldrich is pleased to offer an array of phosphines for C-C, C-N, and C-O bond formation. Chem Files Volume 4 Article 2Keywords: Amidations, Aminations, Applications, Arylations, Catalysis, Coupling reactions, Cross couplings, Ligands, Organic synthesis, Sonogashira Coupling, Suzuki-Miyaura coupling Catalytic Direct Cross-Coupling of Organolithium Compounds with Aryl Chlorides Complex, hindered biaryls have been prepared at temperatures ranging from 1�C to room temperature, or with gentle heating. The Pd-PEPPSI-IPent catalyst nicely couples starting materials containing ac... Keywords: Chromatography, Flash chromatography Copper-Free Sonogashira Coupling of Cyclopropyl Iodides with Terminal Alkynes An efficient palladium-catalyzed cyanation of aryl chlorides is established.
Apr 29, 2011. Copper iodide has been shown to be an effective co-catalyst for the olefin cross metathesis reaction. In particular, it has both a catalyst stabilizing effect due to iodide ion, as well as copperI-based phosphine-scavenging properties that apply to use of the Grubbs-2 catalyst. A variety of Michael acceptors. 1950s – In the presence of various organometallo compounds, olefin metathesis (where the R groups of olefins were swapped with the other) occurred 1970s – Chauvin and colleagues proposed mechanism that seemed to fit Like a dance An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Tris(triphenylphospine)dichlororuthenium(II) Inorganic Syntheses. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. Synthesis and Catalytic Activity of Ruthenium-Indenylidene Complexes for Olefin Metathesis, J. Ed.2007, 84 (12), 1998-2000.1a in chloroform-d1b in chloroform-d All reference spectra obtained from Pappenfus, T. Synthesis and Catalytic Activity of Ruthenium-Indenylidene Complexes for Olefin Metathesis, J.
Feb 4, 2010. Olefin cross metathesis is used to hybridize the polymer structures of two olefin-containing polymers generated by very different polymerization mechanisms. Because of the relative simplicity of olefin metathesis, it often creates fewer undesired by-products and hazardous wastes than alternative organic reactions. For their elucidation of the reaction mechanism and their discovery of a variety of highly active catalysts, Yves Chauvin, Robert H. Schrock were collectively awarded the 2005 Nobel Prize in Chemistry. Most commercially important processes employ heterogeneous catalysts, but well-defined homogeneous catalysts are also active. Commercial catalysts are often based on molybdenum and ruthenium. The heterogeneous catalysts are often prepared by in-situ activation of a metal halide using organoaluminium or organotin compounds, e.g. Well-defined organometallic compounds have mainly been investigated for small scale reactions or academic research. The homogeneous catalysts are often classified as Schrock catalysts and Grubbs' catalysts. Schrock catalysts feature molybdenum(VI)- and tungsten(VI)-based centers supported by alkoxide and imido ligands.
Ruthenium-Catalyzed Olefin Cross-Metathesis of α-Substituted. Vinyl Boronates. Introduction. The development of active, air- and moisture-stable ruthenium alkylidene catalysts i.e. 1 and 2 has allowed olefin metathesis to become a powerful tool in synthetic chemistry.1. As discussed in the previous chapter, a variety of. Olefin Metathesis entails the redistribution of fragments of alkenes by the scission and regeneration of carbon-carbon double bonds mediated by transition metal carbene complexes. DOI: 10.1039/C8PY00233A - see the feature on our news page "Ruthenium-amide Complexes - Synthesis and Catalytic Activity in Olefin Metathesis and in Ring Opening Polymerization"Gawin, A.; Pump, E.; Slugovc, C.; Kajetanowicz, A.; Grela, K. At ICTM special emphasis is given to the following topics: The isomerization of cis- and trans-dichloro ruthenium carbene catalyst-precursors and its implication for the catalysis is one of key topics of the group. The following list provides an overview of recent publications: "."Abbas, M.; Neubauer, M.; Slugovc, C. in Science of Synthesis: N-Heterocyclic Carbenes in Catalytic Organic Synthesis, Nolan, S. "Historical Overview of N-Heterocyclic Carbenes in Alkene Metathesis."Slugovc, C. 10.1021/acs.organomet.5b00715 "Consequences of the Electronic Tuning of Latent Ruthenium-Based Olefin Metathesis Catalysts on Their Reactivity."Żukowska, K.; Pump, E.; Pazio, A. DOI: 10.3762/bjoc.12.17 "Variation of the Sterical Properties of the N-Heterocyclic Carbene Coligand in Thermally Triggerable Ruthenium-Based Olefin Metathesis Precatalysts/Initiators."Pump, E.; Leitgeb, A.; Kozłowska, A.; Torvisco, A.; Falivene, L.; Cavallo, L.; Grela, K.; Slugovc, C. DOI: 10.3762/bjoc.11.158 "Mechanism of the Ru-Allenylidene to Ru-Indenylidene Rearrangement in Ruthenium Precatalysts for Olefin Metathesis."Pump, E.; Slugovc, C.; Cavallo, L.; Poater, A. DOI: 10.1002/9783527674107.ch27 "Thermal effects in polymerisations – a live view differentiating between bulk effects, thermal diffusion, and oxygen inhibition”Geier, R.; Wappl, C.; Freiszmuth, H.; Slugovc, C.; Gescheidt, G. DOI: 10.1055/sos-SD-224-00002"Simple activation by acid of latent Ru-NHC-based metathesis initiators bearing 8-quinolinolate co-ligands.", 154-165. "Chelating Ruthenium Phenolate Complexes: Synthesis, General Catalytic Activity, and Applications in Olefin Metathesis Polymerization."Kozłowska, A.; Dranka, M.; Zachara, J.; Pump, E.; Slugovc, C.; Skowerski, K.; Grela, K. DOI: 10.1002/chem.201403580 "Two commercially available initiators for the retarded ring-opening metathesis polymerization of dicyclopentadiene."Leitgeb, A.; Wappel, J.; Urbina-Blanco, C. DOI: 10.1007/s00706-014-1249-y "Impact of Electronic Modification of the Chelating Benzylidene Ligand in cis-Dichloro-Configured Second-Generation Olefin Metathesis Catalysts on Their Activity."Pump, E.; Poater, A.; Zirngast, M.; Torvisco, A.; Fischer, R.; Cavallo, L.; Slugovc, C. DOI: 10.1002/macp.201300561 "Mixed N-heterocyclic carbene/phosphite ruthenium complexes: the effect of a bulkier NHC." Urbina-Blanco, C.
Olefin cross metathesis based de novo synthesis of a partially protected L-amicetose and a fully protected L-cinerulose derivative. Cross metathesis of a lactate derived allylic alcohol and acrolein is the entry point to a de novo synthesis of 4-benzoate protected L-amicetose and a cinerulose derivative protected at C5 and C1. Keywords: Many drugs and bioactive natural products are glycoconjugates, which contain an aglycon part linked through glycosidic bonds to one or more oligosaccharide side chains . While it was assumed for quite some time that the carbohydrate side chain merely influences the pharmacokinetics, more recent investigations led to the conclusion that the oligosaccharide moiety contributes essentially to the mechanisms of action, e.g., through molecular recognition of a preferred binding site [2-5], thereby ensuring the selectivity of a chemotherapeutic agent. Particularly common are side chains composed of deoxygenated sugars . For example, the kigamicins are bacterial secondary metabolites isolated from Amicolatopsis sp. [7,8] and display both antibiotic and cytotoxic activity . They have a polycyclic xanthone aglycone in common, which is glycosylated at the C14–OH group. In Figure 1 the structure of kigamicin B, which carries a D-amicetose disaccharide unit, is shown as a representative example.
As a result, the stereogenic-at-Mo complexes are generally more effective olefin metathesis catalysts than other Mo-based complexes 3 and 4 or Ru carbene 5. We thus established that alkylidene 2 readily catalyses Z-selective alkene formation through ring-opening/cross-metathesis ROCM with strained oxabicyclic. In recent years, olefin cross metathesis (CM) has emerged as a powerful and convenient synthetic technique in organic chemistry; however, as a general synthetic method, CM has been limited by the lack of predictability in product selectivity and stereoselectivity. Investigations into olefin cross metathesis with several classes of olefins, including substituted and functionalized styrenes, secondary allylic alcohols, tertiary allylic alcohols, and olefins with α-quaternary centers, have led to a general model useful for the prediction of product selectivity and stereoselectivity in cross metathesis. As a general ranking of olefin reactivity in CM, olefins can be categorized by their relative abilities to undergo homodimerization via cross metathesis and the susceptibility of their homodimers toward secondary metathesis reactions. When an olefin of high reactivity is reacted with an olefin of lower reactivity (sterically bulky, electron-deficient, etc.), selective cross metathesis can be achieved using feedstock stoichiometries as low as 1:1. By employing a metathesis catalyst with the appropriate activity, selective cross metathesis reactions can be achieved with a wide variety of electron-rich, electron-deficient, and sterically bulky olefins. Application of this model has allowed for the prediction and development of selective cross metathesis reactions, culminating in unprecedented three-component intermolecular cross metathesis reactions.© 2003 American Chemical Society. A General Model for Selectivity in Olefin Cross Metathesis Arnab K. Gallivan for helpful discussions and encouragement. The authors gratefully acknowledge the generous funding provided by the National Institutes of Health.
Olefin metathesis has become a. cross metathesis and. In those circumstances where a Type 1 olefin reacts with a Type 2 or 3 olefin and the reaction is. The production of fuels and chemicals from renewable resources is increasingly important due to the environmental concern and depletion of fossil fuel. Despite the fast technical development in the production of aviation fuels, there are still several shortcomings such as a high cost of raw materials, a low yield of aviation fuels, and poor process techno-economic consideration. In recent years, olefin metathesis has become a powerful and versatile tool for generating new carbon–carbon bonds. The cross-metathesis reaction, one kind of metathesis reaction, has a high potential to efficiently convert plant oil into valuable chemicals, such as α-olefin and bio-aviation fuel by combining with a hydrotreatment process. In this research, an efficient, four-step conversion of plant oil into bio-aviation fuel and valuable chemicals was developed by the combination of enzymatic transesterification, olefin cross-metathesis, and hydrotreating. Firstly, plant oil including oil with poor properties was esterified to fatty acid methyl esters by an enzyme-catalyzed process. Secondly, the fatty acid methyl esters were partially hydrotreated catalytically to transform poly-unsaturated fatty acid such as linoleic acid into oleic acid. The olefin cross-metathesis then transformed the oleic acid methyl ester (OAME) into 1-decene and 1-decenoic acid methyl ester (DAME).
Jul 12, 2006. Over the past decade, olefin metathesis has become a powerful tool in organic synthesis, and is widely used by chemists in other disciplines as well 1. Alkene cross-metathesis CM Scheme 1 emerged later than the ring-closing process, as many undesired products such as homodimers often plagued. The olefin cross-metathesis (CM) reaction is used extensively in organic chemistry and represents a powerful method for the selective synthesis of differentially substituted alkene products. Surprisingly, efforts to integrate this remarkable process into strategies for aromatic and heteroaromatic construction have not been reported. Such structures represent key elements of the majority of small molecule drug compounds; methods for the controlled preparation of highly substituted derivatives are essential to medicinal chemistry. Here we show that the olefin CM reaction, in combination with an acid cocatalyst or subsequent Heck arylation, provides a concise and flexible entry to 2,5-di- or 2,3,5-tri-substituted furans. These cascade processes portend further opportunities for the regiocontrolled preparation of other highly substituted aromatic and heteroaromatic classes.