Download or read book Aspects of Ring Opening Metathesis Polymerization Using High Oxidation State Tungsten and Molybdenum Alkylidenes written by Kimo B. Yap and published by . This book was released on 1991 with total page 430 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 Ring Opening Metathesis Polymerisation and Related Chemistry written by Ezat Khosravi and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 489 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since the last ASI in Turkey in Sept. 1995, the olefin metathesis has made remarkable strong developments with an incredible speed in various directions. New catalyst systems have been developed which have resulted in the synthesis of novel materials. Other fascinating developments have been the new catalysts for stereoselective metathesis and catalysts with considerable functional group tolerance. These new catalysts in addition to Ring Opening Metathesis Polymerisation (ROMP) and Acyclic Diene Metathesis (ADMET) are now powerful tools for Ring Closing Metathesis (RCM) and have found many applications in the synthesis of natural products. A lot of information has been established about all aspects of the olefin metathesis and there is a vast literature concerning the process, covering the initiators, mechanistic features and applications of this reaction in organic and polymer synthesis. The NATO ASI on rd th ROMP and Related Chemistry took place in Polanica-Zdroj, Poland during 3 to 15 Sept. 2000, to highlight the developments in this area and to discuss the prospects and visions for the year 2000 and beyond. The aims of the ASI were: to provide a platform for dissemination of knowledge; to promote communication between people who have a serious interest in this field of chemistry; to help establishing international scientific contacts and to provide an opportunity for the scientists with an appropriate scientific background to learn of recent developments in this field of science. There were 15 lecturers and 67 participants in this NATO ASI.
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 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 Controlled Ring Opening Metathesis Polymerization by Molybdenum and Tungsten Alkylidene Complexes written by Richard S. Schrock and published by . This book was released on 1988 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt: A new, convenient preparation of tungsten (CHtBu)(NAr)Cl2(dme) (Ar = 2,6-diisopropylphenyl) involves treatment of W(NAr)(OtBu)2(CH2tBu)2 with PCl5 in dimethoxyethane as a final step. From it a variety of complexes of the type W(CHtBu)(NAr)(or)2 (R = alkyl or fluoroalkyl) can be prepared straightforwardly in high yield. Analogous complexes of the type Mo(CHtBu)(NAr)(OR)2 also have been prepared. Complexes in which OR =OtBu will not react with ordinary olefins, but will react with strained cyclic olefins such as norbornene and cyclopentene to give living polymers from which the organic polymer can be cleaved by treatment with aldehydes. Reprints. (jes).
Download or read book Preparation and Reactions of Tantalum Alkylidene Complexes Containing Bulky Phenoxide Or Thiolate Ligands Controlling Ring Opening Metathesis Polymerization Activity and Mechanism Through Choice of Anionic Ligand written by Kevin C. Wallace and published by . This book was released on 1988 with total page 69 pages. Available in PDF, EPUB and Kindle. Book excerpt: We have reported a variety of high oxidation state, electronically unsaturated alkylidyne and (more recently) alkylidene complexes of tungsten and molybdenum that contain bulky alkoxide ligands. We decided to test whether some of the principles we had uncovered in tungsten and molybdenum chemistry could be used to advantage in tantalum chemistry, especially since Ta(CH1Bu)(THF)2Cl3 can be prepared in high yield in two relatively easy steps from TaCl. Tantalum alkylidene complexes have been useful for outlining the principles of olefin metathesis, but none has been long-lived enough to be practical for metathesis of ordinary olefins. Therefore we felt we had a better chance of preparing reagents for Wittig-like reactions or catalysts for the controlled ring-opening of strained cyclic olefins. We also wanted to compare various other supporting ligand systems with alkoxides in order to uncover major differences that might be useful in controlling metathesis activity. In this paper we report the preparation and a comparison of the reactivity of complexes of the type Ta(CH1Bu)X3(THF) where X is a bulky phenoxide or phenyl thiolate ligand. We have found that differences between phenoxide and phenyl thiolate systems are dramatic; the choice determines both activity and mechanism. Yellow Ta(CH1Bu)(DIPP)3(THF) (1; equation 1; DIPP = 2,6-diisopropylphenoxide) is formed in high yield upon treating isolated Ta(CH1Bu)(THF)2Cl3 with 3 eq of LiDIPP. It also can be prepared from Ta(CH1Bu)(THF)2Cl3 that has been generated in situ in ether by addition of excess THF to Ta(CH2(t)Bu)2Cl3. (aw).
Download or read book Handbook of Transition Metal Polymerization Catalysts written by Ray Hoff and published by John Wiley & Sons. This book was released on 2018-04-20 with total page 895 pages. Available in PDF, EPUB and Kindle. Book excerpt: Including recent advances and historically important catalysts, this book overviews methods for developing and applying polymerization catalysts – dealing with polymerization catalysts that afford commercially acceptable high yields of polymer with respect to catalyst mass or productivity. • Contains the valuable data needed to reproduce syntheses or use the catalyst for new applications • Offers a guide to the design and synthesis of catalysts, and their applications in synthesis of polymers • Includes the information essential for choosing the appropriate reactions to maximize yield of polymer synthesized • Presents new chapters on vanadium catalysts, Ziegler catalysts, laboratory homopolymerization, and copolymerization
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 . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Dissertation Abstracts International written by and published by . This book was released on 2004 with total page 692 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 Research in Materials written by Massachusetts Institute of Technology and published by . This book was released on 1996 with total page 382 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 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 Ring opening Metathesis Polymerization Molybdenum VI Alkylidene Catalysts written by Gino Georges Lavoie and published by . This book was released on 1996 with total page 354 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 Research in Materials written by and published by . This book was released on 1992 with total page 508 pages. Available in PDF, EPUB and Kindle. Book excerpt:
