Download or read book Molybdenum Alkylidene Complexes written by Tatiana Pilyugina and published by . This book was released on 2007 with total page 302 pages. Available in PDF, EPUB and Kindle. Book excerpt: (Cont.) Chapter 3. Reactions of Mo Bispyrrolide Complexes with Enantiomerically Pure Diols: In Situ Catalyst Generation and Studies of Olefin Metathesis Reactions In the Fume Hood. Reactions of bispyrrolide molybdenum complexes Mo(NAd)(CHCMe2Ph)(pyr)2 and Mo(N-2-6-i-Pr2C6H3)(CHCMe2Ph)(pyr)2 with (R)-BiphenH2, and (R)-Benz2BitetH2 were examined (pyr = C4H4N, Benz2BitetH2 = 3,3'-dibenzhydryl-5,5',6,6',7,7',8,8'-octahydro-1,1'- binaphthyl-2,2'-diol). The resulting in situ generated catalysts were studied in three olefin metathesis reactions. These systems were found to be as active and enantioselective as the analogous isolated complexes. When the stock solutions of Mo(NAd)(CHCMe2Ph)(pyr)2, Mo(N- 2,6-i-Pr2C6H3)(CHCMe2Ph)(pyr)2, (R)-BiphenH2, and (R)-Benz2BitetH2 were stored in the fume hood over a period of one month, the in situ prepared catalysts were determined to be nearly identical in terms of their catalytic properties to the catalysts generated in situ in the glovebox.

Download or read book Synthesis of Molybdenum and Tungsten Oxo and Imido Alkylidene NHC Complexes and Their Use in Stereoselective Ring Opening Metathesis Polymerization written by Mathis Benedikter and published by Cuvillier Verlag. This book was released on 2021-04-08 with total page 306 pages. Available in PDF, EPUB and Kindle. Book excerpt: Im Rahmen der Dissertation wurden unterschiedliche Aspekte der Olefinmetathese mit Molybdän- und Wolframbasierten Katalysatoren untersucht. Zunächst wurde die Eignung von Molybdän Imido Alkyliden N-heterocyclischen Carben (NHC) Komplexen als Initiatoren für die ringöffnende Metathese-Polymerisation (ROMP) erforscht. Durch Einsatz von chiralen, enantiomerenreinen Norbornenderivaten als Monomer konnte gezeigt werden, dass mit diesen Komplexen selektiv trans-isotaktische Polymere hergestellt werden können. Die beobachtete Selektivität ist dabei stark abhängig von der Ligandensphäre. Des Weiteren konnte vollständig hydriertes, syndiotaktisches Polydicyclopentadien hergestellt und erstmals mittels Schmelzspinnen zu Fasern versponnen werden. Ein weiterer Schwerpunkt der Dissertation lag auf der Entwicklung neuer Katalysatoren für die Olefinmetathese. So wurde eine neue Syntheseroute zur Herstellung kationischer Wolfram Imido Alkyliden NHC Komplexen entwickelt. Durch Anpassung der Ligandensphäre konnten luftstabile kationische Molybdän und Wolfram Imido Alkyliden NHC Komplexe hergestellt werden, die hohe Produktivitäten in der Olefinmetathese von Substraten mit verschiedenen sauerstoff- und schwefelhaltigen funktionellen Gruppen zeigen. Schließlich konnte der erste Molybdän Oxo Alkyliden NHC Komplex hergestellt und charakterisiert werden.

Download or read book Synthesis Structure and Applications of Metallacyclic Alkylidene Complexes of Molybdenum and Tungsten written by Kapil Shyam Lokare and published by . This book was released on 2009 with total page 308 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Ligand Variation in Molybdenum Imido Alkylidene Complexes written by Alejandro Gaston Lichtscheidl and published by . This book was released on 2012 with total page 222 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chapter 1. A general introduction is given. Chapter 2. The biscarboxylate species, Mo(NR)(CHCMe 2Ph)(O 2CPh3)2 (R = 2,6-i-Pr2C6H3, 2,6- Me2C6H3, 2-t-BuC 6H4, or 1 -adamantyl) are compared to newly synthesized bis(terphenylcarboxylate) species, Mo(NR)(CHCMe 2Ph)(O 2CTer)2 (Ter = 2,6-diphenyl-4- methylphenyl or 2,6-diphenyl-4-methoxyphenyl). Preparation of bis(terphenylcarboxylate) species was accomplished through protonolysis of Mo(NR)(CHCMe2R')(Me2Pyr)2 with two equivalents of TerCO2H and one of them was characterized through X-ray crystallography. Photolysis experiments of many of the biscarboxylate complexes led to rate constants for the converstion of anti to syn species, which are much slower than bisalkoxide species. Trimethylphosphine adducts of selected triphenylacetate complexes have been isolated and studied in solution. Protonolysis of Mo(NAr)(CHCMe 2R')(Me 2Pyr)2 (Ar = 2,6-i-Pr 2C6H3) with one equivalent of TerCO2H led to the isolation of a handful of monocarboxylate species, Mo(NAr)(CHCMe 2Ph)(O 2CAr')(Me2Pyr). An X-ray structure of one of them was also characterized. Several of the bis(triphenylacetate) complexes and all of the monocarboxylates are active initiators for the regioselective polymerization of diethyl dipropargylmalonate (DEPDM). In the case of the latter compounds, activity towards olefins is also observed and briefly mentioned.

Download or read book Novel Strategies for the Synthesis of Tungsten VI and Molybdenum VI Imido Oxo Alkylidene NHC Complexes and Their Application in Ring Opening Metathesis Polymerization written by Janis Musso and published by Cuvillier Verlag. This book was released on 2022-05-12 with total page 186 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recently, the synthesis of neutral and cationic group(VI) imido/oxo alkylidene N-heterocyclic carbene (NHC) complexes that tolerate protic functional groups and aldehydes was reported. Unprecedented turnover numbers of up to 1.2 million were found for their silica-supported representatives. Some group(VI) alkylidene NHC complexes even display stability towards moisture and air. Coordination of the NHC to tungsten imido bistriflate precursor complexes, however, can lead to undesired side reactions. This work consequently aimed at the development of novel, more efficient routes to neutral and cationic tungsten imido/oxo alkylidene NHC complexes. In addition, some molybdenum imido alkylidene NHC complexes were targeted. Thereby, the scope of synthetically accessible complexes was broadened and, subsequently, their reactivity in ring-opening metathesis polymerization (ROMP) was probed. Those complexes were used as thermally latent initiators for the ROMP of dicyclopentadiene. Precise determination of the onset temperature of polymerization was achieved via monitoring with differential scanning calorimetry. Furthermore, the selectivity of novel complexes was tested for the formation of stereoregular polymers through ROMP of enantiomerically pure norbornene derivatives, which allowed for the synthesis of up to 98% trans-isotactic or cis-syndiotactic polymers depending on the steric demand of the imido and the alkoxide ligand.

Download or read book Synthesis of Molybdenum VI Alkylidene Complexes as Catalysts for Living Polymerizations of Terminal Acetylenes and Olefin Metathesis written by Harold Hamilton Fox and published by . This book was released on 1993 with total page 558 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Synthesis of New Molybdenum VI Alkylidene Complexes and Ring Opening Metathesis Polymers written by Jin-Kyu Lee and published by . This book was released on 1995 with total page 336 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book High Oxidation State Molybdenum and Tungsten Imido Alkylidene and Metallacycle Chemistry written by W. C. Peter Tsang and published by . This book was released on 2004 with total page 526 pages. Available in PDF, EPUB and Kindle. Book excerpt: (Cont.) unsubstituted tungstacyclobutane complexes (82), ethylene complexes (84), tungstacyclopentane complexes (86), and a heterochiral methylene dimer (85a). The tungstacyclopentane complexes catalyzed slow dimerization of ethylene to 1-butene. The observation of the methylene dimer provides the first direct evidence of a bimolecular decomposition pathway for methylene complexes. Chapter 3 Racemic and enantiomerically pure molybdenum alkylimido alkylidene complexes, Mo(NAd)(CHCMe2Ph)(Biphen) (19d, Ad = 1-adamantyl) and Mo(NAd)(CHCMe2Ph)[Trip]-(THF) (20d) were prepared and structurally characterized. Complex 19d was observed almost exclusively as a syn alkylidene isomer, in contrast with 20d which was observed almost exclusively as an anti-THF adduct. Complexes 19d and 20d are the only reported chiral alkylimido alkylidene complexes for enantioselective olefin metathesis reactions. Complex 19d is the first crystallographically characterized four-coordinate adamantylimido alkylidene complex in its base-free form. It offers unique reactivity and selectivity profiles in tandem AROM/RCM and AROM/CM reactions. Complex 19d is compatible with a variety of common functional groups, including boron-containing reagents. Van't Hoff analyses suggest that the bias toward syn-19d isomer is entropy-driven. Chapter 4: Solvent- and base-free molybdenum methylene complexes, Mo(NAr)(Biphen)(CH2) (114a, Ar = 2,6-i-Pr2C6H3) and Mo(NAd)(Biphen)(CH2) (114d, Ad = 1-adamantyl) ...

Download or read book Molybdenum and Tungsten Alkylidene Complexes for Cis and Trans selective Ring opening Metathesis Polymerization written by Hyangsoo Jeong and published by . This book was released on 2015 with total page 231 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chapter 1 describes the synthesis of tert-butylimido alkylidene complexes for molybdenum and tungsten. A dimer species [chemical formula] served as a bisimido precursor. After alkylation with Grignard reagent, alkylidene formation is accomplished using pyridinium chloride. [chemical formula] crystallizes as a dimer [chemical formula] with a loss of pyridine for each W center. For the case of molybdenum, addition of pentafluorophenol to the diimido dialkyl precursor affords [chemical formula]. Dipyrrolide complexes for both Mo and W are synthesized and isolated as a 2,2'-bipyridine adduct. Addition of a sterically encumbered terphenol along with ZnCl2(dioxane) affords monoalkoxide pyrrolide (MAP) complexes [chemical formula]. Chapter 2 investigates Z-selective ring-opening metathesis polymerization (ROMP) of 3- substituted cyclooctenes (3-RCOEs) by Mo and W MAP catalysts. [chemical formula], [chemical formula], and [chemical formula] all produced >98% [chemical formula]. The key in forming high molecular weight polymer instead of cyclic oligomer species was to run the reaction neat. Surprisingly, the fastest initiator was [chemical formula] among all three MAP species. Polymerization proceeds via a propagating species in which the R group is of C2 position of the propagating chain, giving HT polymers with high regioselectivity. Chapter 3 describes the synthesis and reactivity of compounds containing a tert-butylimido ligand. Chelating alkylidenes can be synthesized either by alkylidene exchange or by traditional routes in forming alkylidene complexes from diimido dialkyl species. A W MAP complex containing a chelating alkylidene can be synthesized and its reactivity is comparable to that of neopentylidene analogue in 1-octene homocoupling. Complexes with a chelating diolate ligand [chemical formula] and [chemical formula] were synthesized. However, attempts to remove the pyridine ligand induced C-H activation of one tertbutyl group on Biphen ligand to form alkyl complexes. Chapter 4 presents the synthesis of high sequence-regular alternating trans-AB copolymers by ROMP initiated by [chemical formula]. Monomers employed were 2,3-dicarbomethoxy-7-isopropylidenenorbomadiene (B), [chemical formula] (B'), cyclooctene (A), and cycloheptene (A'). All four combinations afford structures containing a high degree of monomer alternation. Evidence suggests a catalytic cycle proceeding through a syn alkylidene arising from insertion of B (syn-MB) reacting with A to form an anti alkylidene (anti-MA) and a trans-AB linkage. A MAP complex [chemical formula] [chemical formula] was also found to form trans-poly[A-alt-B'] with >90% alternating dyad sequences. Variations on imido and alkoxide ligands were surveyed as well as both A and B type monomers.

Download or read book Synthesis and Reactivity of Some Molybdenum VI Alkylidene and Alkylidyne Complexes written by John Stephen Murdzek and published by . This book was released on 1988 with total page 1082 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Chiral Molybdenum and Tungsten Imido Alkylidene Complexes as Catalysts for Asymmetric Ring closing Metathesis ARCM written by John Bryson Alexander and published by . This book was released on 1999 with total page 360 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Molybdenum written by E.R. Braithwaite and published by Elsevier. This book was released on 2013-10-22 with total page 681 pages. Available in PDF, EPUB and Kindle. Book excerpt: Molybdenum is an element with an extremely rich and interesting chemistry having very versatile applications in various fields of human activity. It is used extensively in metallurgical applications. Because of their anti-wear properties, molybdenum compounds find wide applications as lubricants - particularly in extreme or hostile environmental situations. Many molybdates and heteropolymolybdates are white and therefore used as pigments. In addition, they are non-toxic and act as efficient corrosion inhibitors and smoke suppressants. Hydroprocessing of petroleum is one of the largest industries employing heterogeneous catalysts. Molybdenum catalysts have shown great promise in the liquefaction of coal and this may develop into one of its most important catalytic uses. The use of molybdenum compounds in homogeneous catalysis is also significant. Three important classes of molybdenum compounds in the solid state are reviewed, viz., oxides, sulphides and halides. The role of molybdenum in inorganic catalysis and enzymes receives prominent mention because of their impact on the progress of science and technology. Further biochemical and enzymic factors are discussed in separate chapters and their reaction to agriculture and animal husbandry. A new classification of covalent compounds which abandons the traditional oxidation state concept allows a powerful approach to the organisation of the complex and rich chemistry of molybdenum. Dramatic colour diagrams of abundances of molybdenum compounds provide broad insights into the important features and trends in the chemistry of molybdenum including reactivity and mechanism. The book is intended for use mainly as a research monograph by the many workers who may encounter molybdenum chemistry or who are looking for its application and potential uses in different technological fields. However, it will also serve as an advanced text for university lecturers and postgraduate students interested in inorganic, physical and industrial chemistry, chemical technology or biochemistry and biotechnology.

Download or read book Structure property Insights Into Molybdenum Imido Alkylidene N heterocyclic Carbene Complexes for Olefin Metathesis written by Mohasin Momin and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book High Oxidation State N heterocyclic Carbene Molybdenum Alkylidene Complexes Functional group Tolerant Olefin Metathesis Catalysts written by Suman Sen and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Chelate stabilized Alkylidene Complexes of Molybdenum and Tungsten written by William Michael Vaughan and published by . This book was released on 1995 with total page 366 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Synthesis and Reactivity of Molybdenum Organometallic Complexes Supported by Amide Ligands written by Adam Scott Hock and published by . This book was released on 2007 with total page 292 pages. Available in PDF, EPUB and Kindle. Book excerpt: (Cont.) Chapter 4. Reactivity of Molybdenum Imido Alkylidene Bis(pyrrolyl) Complexes. The Lewis amphoteric nature of the bis(pyrrolyl) complexes reported in chapter 3 is examined by demonstrating that these complexes react with both trimethylphosphine (at the molybdenum center) and B(C6Fs)3 (at a q5 pyrrolyl nitrogen). A structure of a trimethylphosphine adduct is reported. The bis(pyrrolyl) complexes are found to serve as excellent precursors for the in situ generation of olefin metathesis catalysts at room temperature and millimolar concentration. Furthermore, catalysts not accessible via traditional routes may now be accessed from bis(pyrrolyl) precursors. The bis(pyrrolyl) complexes also react with simple olefins such as ethylene and isobutylene to yield what are proposed to be a bimetallic dimer [Mo(NAr)(NC4H4)2]2 and a 2-propylidene complex via olefin metathesis. The impact of in situ synthesis on syn and anti isomer ratios is discussed as is reactivity with protic reagents other than alcohols.

Download or read book Iron and Molybdenum Complexes Supported by Pincer Ligands written by Steven Ryan Ruark and published by . This book was released on 2016 with total page 135 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since its discovery in the mid 1950’s, olefin metathesis has become one of the most widely used chemical reactions. Olefin metathesis involves the breaking of carbon-carbon double bonds and the redistribution of the fragments to form new olefins by way of a metal alkylidene.6 It is used in industry to convert cheap plant oils into useful products such as alpha olefins, jet fuel and green diesel. The Elevance BioRefinery has the capacity to run this reaction and produce up to 400 million pounds of products per year. The most expensive part in this refinery process is the catalyst itself. The catalyst currently used is an alkylidene complex of ruthenium—an expensive and rare metal. This has led the Schrodi group to explore the possibility of developing catalysts based on abundant and cheap metals such as iron or molybdenum.40,41 We first attempted to support iron with a tridentate pincer ligand, OiPrPONOP, however the ligand was not robust enough and more than one ligand was required to adequately protect the iron xv center. Ultimately, the ligand was reacted with Fe(PMe3)4 to make (OiPrPONOP)Fe(PMe3)2. This complex is very stable and unreactive, preventing its transformation into any catalytic species. We then turned our attention to a pincer OCO-NHC ligand. This ligand was able to stabilize an iron tricyclohexyphosphine complex, (OC-NHC)FePCy3, However, attempts to react this complex with diazo compounds to form an iron alkylidene (OCO-NHC)Fe=CHR were unsuccessful. Further studies focused on replacing the PCy3 ligand with pyridines, in an attempt to make the complex more labile. However, the resulting species proved much too sensitive to water and was difficult to isolate and characterize. Inspired by the research done by the Chirik group where they reduced several arylpyridinediimine ( ArPDI) ironII complexes into a reduced N2-bridged complex. They reported the bound N2 molecules would readily exchange with 15N2 and ultimately they were able to form an iron alkylidene complex. However, the complex was not metathesis active.54,42 We successfully reduced MesPDIFeBr2 into the bis-N2 complex but the complex refused to react cleanly in attempts to make iron alkylidene species. We also explored the possibility of forming a molybdenum alkylidene supported by a tridentate iPrPONOP ligand. After successfully forming iPrPONOPMoCl3 we tried several strategies to form and isolate a molybdenum alkylidene. We attempted a similar reduction as the iron species trying to access a bis-N2 bridged molybdenum complex but the reaction resulted in decomposition of the complex. We then attempted ‘Schrock type’ chemistry by reacting the iPrPONOPMoCl3 complex with Grignard reagents.81 However, this strategy resulted in decomposition as well. We successfully performed ring opening metathesis polymerization (ROMP) of norbornene by adding Grignard reagents to several different tridentate supported MoCl3 precatalysts. Select polymers were then analyzed for cis content by 1 H NMR to probe for serioregularity. The only precatalyst to have more than 50% cis content was the BinapthPONOPMoCl3 / methyl- and trimetylsilylmethlyl-Grignard reagents but only when run at 25 °C. xvi We were able to perform ROMP of dicyclopentadiene (DCPD) with the molybdenum complex / Grignard reagents. However, while the fully polymerized product is extremely hard and transparent we could only achieve a soft nontransparent product, indicating incomplete polymerization.