EBookClubs

Read Books & Download eBooks Full Online

EBookClubs

Read Books & Download eBooks Full Online

Book Chiral Molybdenum and Tungsten Imido Alkylidene Complexes as Catalysts for Asymmetric Ring closing Metathesis ARCM

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:

Book High Oxidation State Molybdenum and Tungsten Imido Alkylidene and Metallacycle Chemistry

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) ...

Book Synthesis and Reactivity of High Oxidation State Tungsten and Molybdenum Olefin Metathesis Catalysts Bearing New Imido Ligands

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).

Book Synthesis of Molybdenum and Tungsten Oxo and Imido Alkylidene NHC Complexes and Their Use in Stereoselective Ring Opening Metathesis Polymerization

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.

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

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.

Book Dissertation Abstracts International

Download or read book Dissertation Abstracts International written by and published by . This book was released on 1996 with total page 860 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Alkyl and Carbonyl Complexes of Molybdenum and Tungsten

Download or read book Alkyl and Carbonyl Complexes of Molybdenum and Tungsten written by K. E. Hill and published by . This book was released on 1982 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Synthesis Characterization and Rotational Isomerization of Chelate Stabilized Tungsten 6 Alkylidenes Olefin Metathesis Polymerization Catalyst Precursors

Download or read book Synthesis Characterization and Rotational Isomerization of Chelate Stabilized Tungsten 6 Alkylidenes Olefin Metathesis Polymerization Catalyst Precursors written by Laura L. Blosch and published by . This book was released on 1993 with total page 480 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book The Evolution of Molybdenum and Tungsten Olefin Metathesis Catalysts

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).

Book Synthesis and Reactivity of Molybdenum and Tungsten Alkylidyne Complexes

Download or read book Synthesis and Reactivity of Molybdenum and Tungsten Alkylidyne Complexes written by Laughlin G. McCullough and published by . This book was released on 1984 with total page 282 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Synthesis Reactivity and Electronic Structure of Molybdenum and Tungsten Complexes

Download or read book Synthesis Reactivity and Electronic Structure of Molybdenum and Tungsten Complexes written by Kristine Quinlan and published by Ann Arbor, Mich. : University Microfilms International. This book was released on 2002 with total page 378 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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

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.

Book Complexes of Molybdenum and Tungsten with Sulphur donor Ligands

Download or read book Complexes of Molybdenum and Tungsten with Sulphur donor Ligands written by Charles Graham Young and published by . This book was released on 1982 with total page 217 pages. Available in PDF, EPUB and Kindle. Book excerpt: