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 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. This book was released on 2022-05-12 with total page 0 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 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 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 Synthesis and Reactivity of High Oxidation State Tungsten and Molybdenum Olefin Metathesis Catalysts Bearing New Imido Ligands written by Jonathan Clayton Axtell and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Chapter 1 details the synthesis of tungsten imidoalkylidene compounds bearing strongly electron-withdrawing imido ligands. An alternative synthesis involving the treatment of WCl6 with 4 equivalents of N-trimethylsilyl-substituted anilines and subsequent workup with 1,2-dimethoxyethane (DME) has been employed to form complexes of the type W(NAr)2C12(dme); syntheses employing WO2C 2(dme) as the tungsten precursor were unsuccessful. Alkylation with neopentylmagnesium chloride (ClMgNp) and subsequent treatment with trifluoromethanesulfonic acid (HOTf) affords imidoalkylidene species W(NAr)(CHCMe 3)(OTf)2(dme) (OTf = trifluoromethanesulfonate); analogous neophylidene ([W]CHCMe 2Ph) species could not be made under these conditions. Treatment of these compounds with two equivalents of LiO(2,6-(CHCPh 2)C6H3)-Et2O affords the bisaryloxide complexes of the type W(NAr)(CHCMe3)(OR)2. Ring-Opening Metathesis Polymerization (ROMP) studies using a series of these bisaryloxides show that rates of ROMP increase as the electron-withdrawing power of the substituents on the imido ligand increase if steric bulk about the metal center is held constant. A similar trend between two bisaryloxides is observed for anti-to-syn alkylidene rotation rates at 50*C in toluene-d8 . Difficulties synthesizing bis-pyrrolide complexes of the type W(NAr)(CHCMe3)(pyr)2 precluded their use as catalyst precursors; some MAP species containing the more sterically encumbering 2,5-dimethylpyrrolide ligand are presented and the metathesis activity of MAP species bearing the 2,5-dimethylpyrrolide ligand is discussed. Chapter 2 introduces Mo and W complexes bearing the current extreme in sterically bulky imido ligands, the NHIPT (HIPT = 2,6-(2,4,6-iPr 3CH2)CH3) ligand, in an effort to generate all anti alkylidene species. A non-traditional synthetic route is employed in order to install this ligand first as an anilide, and after subsequent proton transfer, as an imido ligand to form a mixed imido species of the type M(NHIPT)(N'Bu)(NH'Bu)Cl. Addition of one equivalent of 2,6-lutidinium chloride, followed by alkylation affords dialkyl species M(NHIPT)(N'Bu)Np 2, and treatment with three equivalents of pyridinium chloride yields all anti imidoalkylidene dichloride species as mono-pyridine adducts, M(NHIPT)(CHCMe 3)C 2(py) (M = Mo, W). General reactivity, including strategies for removal of the pyridine adduct as well as substitution and metathesis chemistry, are discussed. ROMP of MPCP (MPCP = 3-methyl-3-phenylcyclopropene) by a Mo-based MAP species bearing the NHIPT ligand yields predominantly cis,syndiotactic poly(MPCP) and in the homo-metathesis of 1 -octene yields ~81% cis-7-tetradecene. The possible source of trans olefinic product is addressed. Chapter 3 presents the synthesis of the first (1-adamantyl)imido species of tungsten. The functional equivalent of common bisimido precursors for other Mo/W alkylidene species, [W(NAd) 2C 2(AdNH2)1 2, is shown to be a dimer stabilized by hydrogen-bonding interactions between adamantylamine protons and adjacent chlorides bound to the second metal of the dimer. Subsequent alkylation with ClMgNp affords the expected dialkyl species, and treatment with three equivalents of 3,5-lutidinium chloride affords imidoalkylidene complex W(NAd)(CHCMe 3)(C) 2(lut)2 (lut = 3,5-dimethylpyridine). The most desirable synthetic route toward monoalkoxide pyrrolide (MAP) species proceeds through a monoaryloxide monochloride intermediate W(NAd)(CHCMe 3)(Cl)(OAr)(lut) (Ar = 2,6-(2,4,6-Me 3)C6H3, 2,6-(2,4,6-'Pr 3)C6H3). Removal of lutidine with B(C6 F5 )3 and subsequent treatment with lithium pyrrolide affords W(NAd)(CHCMe3)(pyr)(OAr) (pyr = pyrrolide); 2,5-dimethylpyrrolide analogues (W(NAd)(CHCMe3)(Me2pyr)(OAr) can be accessed via protonolysis by HOAr from W(NAd)(CHCMe3)(Me2pyr)2(lut).

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 Synthesis and Reactivity of Molybdenum and Tungsten Bis tri tert butylsiloxide Imido and Oxo Complexes written by Devon Charles Rosenfeld and published by . This book was released on 2005 with total page 402 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Organoimido Complexes of Molybdenum and Tungsten written by Mark W. Denny and published by . This book was released on 1995 with total page 332 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 Organomolybdenum and Tungsten Complexes as Ring Opening Metathesis Polymerization Catalysts written by Jim Aloysius Maria Brandts and published by . This book was released on 1999 with total page 121 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Synthesis Characterization and Reactivity of Molybdenum and Tungsten Imido Complexes of Relevance to Alkene Dimerization written by and published by . This book was released on 2009 with total page 212 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Evolution of Molybdenum and Tungsten Olefin Metathesis Catalysts written by Annie Jinying Hannah King and published by . This book was released on 2010 with total page 288 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chapter 1: Reaction of Mo(NR)(CHR')(OTf)2(dme) (R = 2,6-i-Pr2C6H3 (Ar), 2,6-Me2C6H3 (Ar'), 2,6-Cl2C6H3 (ArCl), 1-adamantyl (Ad); R' = CMe2Ph, CMe3; dme = dimethoxyethane) with the lithium salt of ArCl-nacnac ([2,6-Cl2C6H3NC(Me)]2CH), led to complexes of the type Mo(NR)(CHCMe2R')(OTf)(ArCl-nacnac). Treatment of these compounds with Na{BArF 4} (ArF = 3,5-(CF3)2C6H3) afforded rare examples of cationic imido alkylidene complexes, {Mo(NR)(CHR')(OTf)(ArCl-nacnac)}{BArF 4}. Addition of {HNMe2Ph}{BArF 4} to Mo(NR)(CHR')(L)2 (L = NC4H4 (Pyr), 2,5-Me2NC4H2 (Me2Pyr)) in THF produced {Mo(NR)(CHR')(L)(THF)x}{BArF 4} (x = 2 for Me2Pyr or 3 for Pyr). Addition of alcohol or phenol to {Mo(NAr)(CHCMe2Ph)(Pyr)(THF)3}{BArF 4} produced {Mo(NAr)(CHCMe2Ph)(OR")(THF)x}{BArF 4} (R" = CMe(CF3)2 (x = 2 or 3), Ar (x = 1), Ad (x = 2)). Complexes Mo(NAr)(CHCMe2Ph)(MesPyr)2 (MesPyr = 2- mesitylpyrrolide), Mo(NAd)(CHCMe3)(MesPyr)2, and Mo(NAr)(CHCMe2Ph)(OTf)(BinaphPPh2) (BinaphPPh2 = (R)-2'-(diphenylphosphino)- [1,1'-binaphthalen]-2-oxide) were also generated. The solid-state structures of Mo(NAr)(CHCMe2Ph)(OTf)(ArCl-nacnac), {Mo(NAr)(CHCMe2Ph)(ArClnacnac)}{ BArF 4}, {Mo(NAr)(CHCMe2Ph)(Pyr)(THF)3}{BArF 4}, {Mo(NAr)(CHCMe2Ph)(OCMe(CF3)2)(THF)3}{BArF 4}, {Mo(NAr)(C2H4)(OCMe(CF3)2)(THF)3}{BArF 4}, {Mo(NAr)(CH2CMe2Ph)(OAr)2}{BArF 4}, Mo(NAr)(CHCMe2Ph)(MesPyr)2, and Mo(NAr)(CHCMe2Ph)(OTf)(BinaphPPh2) have been determined by X-ray diffraction. The initial reactivity with simple olefins employing many of these new alkylidenes was explored. Chapter 2: Two diastereomers of the MAP (monoaryloxidepyrrolide) species, W(NAr)(CH2)(Me2Pyr)(OBitetBr2) (OBitetBr2 = (R)-3,3'-dibromo-2'-(tertbutyldimethylsilyloxy)- 5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl-2-olate), were generated through addition of HOBitetBr2 to W(NAr)(CH2)(Me2Pyr)2. The unsubstituted tungstacyclobutane species, W(NAr)(C3H6)(Me2Pyr)(OBitetBr2), was isolated by exposing the methylidene species to ethylene. A variety of NMR experiments were carried out on the methylidene and metallacycle to elucidate the exchange process between these species. Neophylidene W(NR)(CHCMe2Ph)(Me2Pyr)(OTPP) (OTPP = 2,3,5,6-tetraphenylphenoxide), methylidene W(NR)(CH2)(Me2Pyr)(OTPP), and 6 tungstacyclobutane W(NR)(C3H6)(Me2Pyr)(OTPP) were prepared. Treatment of W(NAr)(CH2)(Me2Pyr)(OTPP) with PMe3 yielded yellow W(NAr)(CH2)(Me2Pyr)(OTPP)(PMe3). NMR studies on compounds W(NAr)(C3H6)(Pyr)(OHIPT) (OHIPT = 2,6-bis-(2,4,6-triisopropylphenyl)phenoxide) and Mo(NAr)(C3H6)(Pyr)(OHIPT) were carried out to examine the exchange process between the metallacyclobutane and the methylidene. Compounds W(NAr)(C3H6)(Me2Pyr)(OBitetBr2), W(NAr)(CH2)(Me2Pyr)(OTPP), W(NAr)(CH2)(Me2Pyr)(OTPP)(THF), W(NAr)(CH2)(Me2Pyr)(OTPP)(PMe3), W(NAr)(C3H6)(Me2Pyr)(OTPP), Mo(NAr)(CH2)(Pyr)(OHIPT), Mo(NAd)(CHCMe3)(Pyr)(OHIPT), and W(NAr)(C3H6)(Pyr)(OHIPT) were crystallographically characterized. Chapter 3: Molybdenum and tungsten catalysts of the type M(NR)(CHR')(Pyr)(OR'') were prepared for highly Z-selective homocoupling metathesis of terminal olefins. Substrates screened were: 1-hexene, 1-octene, allylbenzene, allyltrimethylsilane, methyl-9-decenoate, methyl- 10-undecenoate, allylboronic acid pinacol ester, allylbenzylether, allyltosylamide, Nallylaniline, allyloxy(tert-butyl)dimethylsilane, and allylcyclohexane. Homocoupled products were isolated in moderate yields employing 1 mol% catalyst loading and with90% Z-selectivity. Chapter 4: Exposing Mo(NAr)(C2H4)(MesPyr)2 to two equivalents of HOCH(CF3)2 afforded Mo(NAr)(C2H4)(OCH(CF3)2)2(Et2O). Mo(NAr)(C2H4)(OCH(CF3)2)(Et2O) was shown to isomerize and metathesize olefins such as propene, 1-hexene, and 1-octene at elevated temperatures. Evidence of isomerization and olefin metathesis was also observed with complexes Mo(NAd)(C2H4)(Pyr)(OHIPT) and Mo(NAr)(C2H4)(Me2Pyr)(OAr).

Download or read book Metathesis Polymerization written by Michael R. Buchmeiser and published by Springer. This book was released on 2010-02-12 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 1 T.W. Baughman, K.B. Wagner: Recent Advances in ADMET Polymerization.- 2 G. Trimmel, S. Riegler, G. Fuchs, C. Slugovc, F. Stelzer: Liquid Crystalline Polymers by Metathesis Polymerization.- 3 M.R. Buchmeiser: Regioselective Polymerization of 1-Alkynes and Steroselective Cyclopolymerization of alpha, omega -Heptadiynes.

Download or read book Studies on Synthesis Properties and Reactions of High valent Oxo Molybdenum and Tungsten Complexes written by Fu-Min Su and published by . This book was released on 1986 with total page 166 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Strategic Applications of Named Reactions in Organic Synthesis written by Laszlo Kurti and published by Elsevier. This book was released on 2005-04-29 with total page 808 pages. Available in PDF, EPUB and Kindle. Book excerpt: Kurti and Czako have produced an indispensable tool for specialists and non-specialists in organic chemistry. This innovative reference work includes 250 organic reactions and their strategic use in the synthesis of complex natural and unnatural products. Reactions are thoroughly discussed in a convenient, two-page layout--using full color. Its comprehensive coverage, superb organization, quality of presentation, and wealth of references, make this a necessity for every organic chemist. - The first reference work on named reactions to present colored schemes for easier understanding - 250 frequently used named reactions are presented in a convenient two-page layout with numerous examples - An opening list of abbreviations includes both structures and chemical names - Contains more than 10,000 references grouped by seminal papers, reviews, modifications, and theoretical works - Appendices list reactions in order of discovery, group by contemporary usage, and provide additional study tools - Extensive index quickly locates information using words found in text and drawings

Download or read book Synthesis and Reactivity of High Oxidation State Molybdenum Catalysts for Ring Opening Metathesis Polymerization of Olefins written by Guillermo Carlos Bazan and published by . This book was released on 1990 with total page 664 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Synthesis Characterization and Catalytic Activity of Molybdenum VI Di and Monooxo Aryloxides written by Mauricio Quiroz-Guzmán and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The chemistry of molybdenum is immensely rich and diverse. Molybdenum is essential for life, and has many applications in industry. The first chapter offers a general perspective of the chemistry of molybdenum in high oxidation states dominated by diverse oxo species, such as the MoO22+ and MoO4+ units that are focus of my research. I describe the importance of MoO22+ complexes as models for the active sites of oxo transfer molybdoenzymes (e.g. DMSO oxidase) and for industrial heterogeneous transformation such as the SOHIO process (one of our ultimate goals). I also outline the importance of MoO4+ complexes as procatalysts for metathesis polymerization and as models of deoxygenated active sites of MoO22+ oxygen catalysts that have triggered our interest. The second chapter introduces the synthesis and full characterization of 4-, 5- and 6-coordinated MoO2(OAr)2L0-1 complexes with bulky aryloxide ligands, starting from the MoO2Cl2 or MoO2Cl2(DMF)2 precursors. Steric and electronic modifications in the aryloxide moieties were performed in order to understand their effect in the final structure and yields of the synthesized complexes. The nature and mechanism of formation of the radical species detected in their synthesis is proposed. The third chapter presents the facile synthesis of varios MoO(OAr)4-nCln complexes starting from the MoO2Cl2 precursor. Their mechanism of formation is proposed and the supporting evidence for this new reaction is provided. Steric and electronic modifications in the aryloxide moieties were used to study their structural and electronic effects in the MoO4+ complexes. The fourth chapter outlines the synthesis of Mo(VI) monooxo bisphenoxides with a characteristic cis-chloro cis-bisphoxide arrangement around the MoO4+ unit. Electronic and steric modifications in the bisphenoxide rings were done to determine their effect in the structure and reactivity of the final complexes. The fifth chapter introduces the application of the synthesized MoO(OAr)4-nCln and MoO(bisphenoxides)2Cl2 complexes as procatalysts for olefin metathesis polymerization of norbornene. The correlation between structure and reactivity of the procatalyst is discussed.