Download or read book Synthesis and Characterization of Heterogeneous Rhenium and Molybdenum Catalysts Applications in Olefin Metathesis and Olefin Epoxidation written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The present dissertation address the synthesis and characterization of novel heterogeneous Rhenium and Molybdenum catalysts, as well as their applications in the olefin metathesis and olefin epoxidation. Acetylperrhenate was grafted on mesoporous silica carrier with various crystal structure and acidity. These novel materials were characterized using IR-, XRD- and NMR-spectroscopy, and applied as catalysts in the olefin epoxidation showing high activity and selectivity. Furthermore, Trimethyldioxorhenium and Cyclopentadienyl-methyl-tricarbonylmolybdenum were grafted on gamma-Alumina. The emerged surface species were characterized using IR- and solid state NMR-spectroscopy. Both systems were successfully applied as catalysts for the metathesis of Propane in batch and CSTR-reactors.

Download or read book Synthesis and Characterization of Homogeneous Rhenium Catalysts Applications in Olefin Epoxidation and Olefin Metathesis written by Su Li 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 Rhenium and Molybdenum Oxo Complexes written by Ana Santos and published by . This book was released on 2000 with total page 205 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Rhenium Molybdenum and Tungsten Organometallic Homogeneous Catalysts Synthesis Characterisation and Application in Olefin Epoxidation written by and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The present manuscript deals with the synthesis and catalytic applications of organometallic transition metal compounds. First, the manuscript describes the synthesis and characterization of Schiff base adducts of methyltrioxorhenium (VII) and its application in olefin epoxidation catalysis with H2O2 as the oxidant. Second, the mechanistic features of the epoxidation reaction with cyclopentadienyl molybdenum alkyl complexes are described. Finally, a new family of highly stable cyclopentadienyl molybdenum and tungsten ansa complexes with cycloalkyl units as bridging moieties is reported. The remarkable epoxidation capabilities at moderate temperatures of these novel complexes are studied as well as being compared with those of previously synthesised related compounds.

Download or read book Organorhenium and Organomolybdenum Oxides written by Simone Antonia Hauser and published by . This book was released on 2012 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book High oxidation state Molybdenum and Tungsten Monoalkoxide Pyrrolide Alkylidenes as Catalysts for Olefin Metathesis written by Erik Matthew Townsend and published by . This book was released on 2014 with total page 195 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chapter 1 describes work toward solid-supported W olefin metathesis catalysts. Attempts to tether derivatives of the known Z-selective catalyst W(NAr)(C3H6)(pyr)(OHIPT) (Ar = 2,6- diisopropylphenyl, pyr = pyrrolide; HIPT = 2,6-bis-(2,4,6-triisopropylphenyl)phenyl) to a modified silica surface by covalent linkages are unsuccessful due to destructive interactions between W precursors and silica. W(NAr)(C3H6)(pyr)(OHIPT) and W(NAr)(CHCMe2Ph)(pyr)(OHIPT-NMe2) (HIPT-NMe 2 = 2,6-bis-(2,4,6-triisopropylphenyl)-4- dimethylaminophenyl) are adsorbed onto calcined alumina. W(NAr)(C 3H6 )(pyr)(OHIPT) is destroyed upon binding to alumina, while W(NAr)(CHCMe 2Ph)(pyr)(OHIPT-NMe 2) appears to bind through a non-destructive interaction between the dimethylamino group and an acidic surface site. The heterogeneous catalysts perform non-stereoselective metathesis of terminal olefins, and W(NAr)(CHCMe2Ph)(pyr)(OHIPT-NMe2) can be washed off the surface with polar solvent and perform solution-phase Z-selective metathesis. Chapter 2 details selective metathesis homocoupling of 1,3-dienes with Mo and W monoalkoxide pyrrolide (MAP) catalysts. A catalytically relevant vinylalkylidene complex, Mo(NAr)(CHCHCH(CH3)2)(Me2pyr)(OHMT) (HMT = 2,6-bis(2,4,6-trimethylphenyl)phenyl; Me2pyr = 2,5-dimethylpyrrolide), is isolated. A series of Mo and W MAP catalysts is synthesized and tested for activity, stereoselectivity, and chemoselectivity in 1,3-diene metathesis homocoupling. Catalysts containing the OHIPT ligand display excellent selectivity in general, and W catalysts are less active but more selective than their Mo counterparts. Chapter 3 recounts the synthesis and characterization of several heteroatom-substituted alkylidene complexes with the formula Mo(NAr)(CHER)(Me2pyr)(OTPP) (TPP = 2,3,5,6- tetraphenylphenyl; ER = OPr, N-pyrrolidinonyl, N-carbazolyl, pinacolborato, trimethylsilyl, SPh, or PPh2). Synthesis proceeds via alkylidene exchange between Mo(NAr)(CHR)(Me2pyr)(OTPP) (R = H, CMe2Ph) and a CH2CHER precursor. Each complex behaves similarly to known MAP complexes in olefin metathesis processes; the electronic identity of ER has little effect on catalytic properties. Distinctive features of alkylidene isomerism and catalyst resting state are examined. Chapter 4 contains synthetic and catalytic studies of thiolate-containing Mo and W imido alkylidene complexes. The species M(NAr)(CHCMe 2Ph)(pyr)(SHMT) (M = Mo or W), Mo(NAr)(CHCMe2Ph)(Me2pyr)(STPP), and Mo(NAr)(CHCMe2Ph)(STPP)2 are synthesized by substitution of the appropriate thiol or thiolate ligands for pyrrolide or triflate ligands in metal precursors. These complexes show similar structural and spectral characteristics to alkoxidecontaining species. The thiolate complexes and their alkoxide analogues are compared for activity and selectivity in metathesis homocoupling and ring-opening metathesis polymerization processes. In general, thiolate catalysts are slower and less selective than alkoxide catalysts.

Download or read book 1 New Molybdenum Catalysts for Alkyl Olefin Epoxidation written by Judith Marie Mitchell and published by . This book was released on 2003 with total page 484 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Olefin Metathesis and Polymerization Catalysts written by Yavuz Imamogammalu and published by Springer. This book was released on 2012-10-13 with total page 571 pages. Available in PDF, EPUB and Kindle. Book excerpt: Olefin metathesis reaction can be considered as one of the most successful organic reactions with many applications in the low molecular weight range and also in the polymer field. The use of catalysts with their selective and effective transformation properties in olefin metathesis I polymerization systems is a growing interest. There has been great effort and competition in developing active and commercially useful catalysts. The main aim of this ASI was to gather several research groups and also the people from industry. to present existing knowledge and latest results in the field. A wide range of topics through homogeneous and heterogeneous aspects have been considered. Attention has been drawn to the metal-carbene and metallacyclobutane complexes as active species, the initiation mechanisms, the stereochemistry and thermodynamics of these reactions. New catalytic systems for the metathesis of alkenes and alkynes and fot' ring opening polymeriZation I block copolymerization reactions have been introduced. Spectroscopic studies for the characteriZation of catalysts, simulation studies explaining the function of chain carrier species and polymer degradation have also been covered. A detailed industrial report concerning the patents and applications in olefin metathesis I cyc1001efin polymerization area, fabrication and derivation has been presented. This volume contains the main lectures and seminars given at the NATO Advanced Study Institute on " Olefin Metathesis and Polymerization Catalysts: Synthesis, Mechanism and Utilization", held at Akcay. Babkesir. Turkey between 10th and 22nd September 1989.

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 Rhenium catalyzed Oxygen atom Transfer Reactions written by Eric C. Brown and published by . This book was released on 2002 with total page 406 pages. Available in PDF, EPUB and Kindle. Book excerpt: In situ reduction of hydrido-tris-(3,5-dimethylpyrazolyl)borato(trioxo) rhenium(V) with triphenylphosphine or triethylphosphite leads to a reactive rhenium(V) species that catalytically deoxygenates epoxides at 75-105°C. The reaction is stereospecific, except for trans- and cis-butene oxide which formed minor amounts of the opposite isomer. A variety of different functional groups were tolerated and even epoxides that reacted slowly could be pushed to greater than 95% conversion given extended time and/or higher temperature. The absence of clustering processes shows how the choice of ligand can have a major influence on the design of the catalytic cycle. The rhenium(V) species formed from reduction of Tp'ReO3 was identified as Tp'Re(O)(OH)2. Tp'Re(O)(OH)2 reacted with ethanol and HCl to form ethoxide and hydroxo chloride complexes, respectively. In addition, Tp'Re(O)(OH)2 was an excellent catalytic and stoichiometric reagent for the deoxygenation of epoxides and sulfoxides. Loss of water from Tp'Re(O)(OH)2 to form the catalytically active species Tp'Re02 was shown to be a necessary preequilibrium process. The kinetic behavior of the catalytic system is complex. First-order behavior in [Re][subscript T], zero-order dependence in [PPh3] and saturation behavior for epoxide were observed. The reversible formation of a coordinated epoxide complex was proposed to explain the saturation behavior. The epoxide complex was shown experimentally and computationally to engage in two separate reactions: ring expansion to form a syn-diolate complex, and direct fragmentation to alkene and trioxide. A steady-state concentration of diolate is eventually reached explaining a "burst" of alkene production prior to generation of a pseudo-zero-order catalytic system. The diolate formed is the syn-isomer, which is the kinetically formed product. Direct epoxide fragmentation is the primary source of alkene. This process was determined to be four times faster than ring expansion for cis-stilbene oxide. The synthesis and characterization of a tethered-epoxide Cp* rhenium trioxide complex has been achieved. Reduction of this complex leads to an unsaturated rhenium(V) species that is immediately complexed by the tethered epoxide. Experimental data and molecular mechanics modeling support intramolecular coordination of the epoxide to the rhenium center. These results confirm that the coordinate epoxide is a viable intermediate in rhenium-catalyzed epoxide deoxygenations.

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:

Download or read book Synthesis and Application of New Ruthenium Based Olefin Metathesis Catalysts written by Roman Savka and published by . This book was released on 2014 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Synthesis of Molybdenum Olefin Metatheses Catalysts Through Protonation Reactions written by Amritanshu Sinha and published by . This book was released on 2006 with total page 352 pages. Available in PDF, EPUB and Kindle. Book excerpt: (Cont.) It was observed that catalytically active species for metathesis reactions can be generated by another Mo (d2) species, Mo(NArcl)(Biphen)(H2C=CH2)(ether) (NArc, = N-2,6-C12C6H3, Biphen2 = 3,3'-di-t-butyl-5,5',6,6'-tetramethyl-1,1'-biphenyl-2,2'-diolate) that could effect the ring-opening metathesis polymerization of norbornene. A mixture of Mo(NArcl)(Biphen)(H2C=CH2)(ether) and 20 equivalents of diallylether in benzene-d6 when treated with 10 equivalents of norbornene gives 54% conversion to dihydrofuran in 10 days.

Download or read book Mechanisms and Catalyst Design for Heterogeneous Olefin Metathesis written by Daniel Francis Consoli and published by . This book was released on 2019 with total page 186 pages. Available in PDF, EPUB and Kindle. Book excerpt: Olefin metathesis offers a promising technology for on-purpose production of propylene and has been implemented in several industrial processes including the Lummus Olefin Conversion Technology. However, current metathesis technology cannot produce propylene cheaply and efficiently due to reliance on decades-old catalyst technology like tungsten oxide on silica. This poor performance can be attributed to a lack of understanding of heterogeneous metathesis reaction mechanisms and the catalysts involved. Current understanding proposes that olefin metathesis follows the Chauvin mechanism in which olefins coordinate with catalytic metal carbenes to form metallacyclobutanes that then rearrange into metathesis products. While this mechanism has been proven for homogenous metathesis catalysts, for which the 2005 Nobel Prize was awarded, the mechanism over heterogeneous catalysts may be more complicated as metal carbenes do not necessarily exist over freshly prepared material. In this thesis, we present a complete mechanistic cycle for heterogeneous olefin metathesis that comprises carbene site formation, stable metathesis, and active site decay. We demonstrate why this expanded mechanism is necessary to explain reaction order behavior for propylene on WO3/SiO2 and the presence of site formation byproducts during isobutene self-metathesis. Furthermore, we leverage our knowledge of the complete mechanism to introduce a secondary olefin to promote active site formation and, consequently, overall metathesis rate. Finally, we utilize our understanding of the importance of site formation to synthesize catalysts supported on tunable zeolite and metal organic framework materials that optimize metal-support interaction and metathesis rates. In sum, an improved understanding of the heterogeneous olefin metathesis mechanism has led to improvements in catalytic design, material characterization, and reactor operation.

Download or read book Synthesis and Characterization of Supported Organometallic Rhodium I Catalysts written by Donald Nilan Marquardt and published by . This book was released on 1974 with total page 252 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Design Synthesis and Applications of Sulfur ruthenium Based Catalysts for Light Directed Olefin Metathesis Reactions written by Efrat Levin and published by . This book was released on 2015 with total page 230 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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: