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Author : Joseph Eric Pelati
Publisher :
ISBN 13 :
Total Pages : 312 pages
Book Rating : 4.3/5 (9 download)
Download or read book Further Studies of the Synthesis and Reactivity of Molybdenum-imido Compounds written by Joseph Eric Pelati and published by . This book was released on 1988 with total page 312 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Jonathan Clayton Axtell
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (919 download)
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).
Author : Jia Min Chin
Publisher :
ISBN 13 :
Total Pages : 188 pages
Book Rating : 4.:/5 (655 download)
Download or read book Synthesis and Studies of Mo and W Complexes for 2N Reduction written by Jia Min Chin and published by . This book was released on 2010 with total page 188 pages. Available in PDF, EPUB and Kindle. Book excerpt: A series of monopyrroletriamine ligands [Arpyr(Ar')2]H3 of the form ArC4H2NHCH2N(CH2CH2NHAr')2 (Ar = 2,4,6-mesityl (Mes), 2,4,6-triisopropylphenyl (TRIP); Ar' = C6F5, 2-tolyl (o-tol), naphthyl, 3,5-(2,4,6-triisopropylphenyl)phenyl (HIPT), 3,5- dimethylphenyl, 3,5-di-tert-butylphenyl were synthesized. [Mespyr(C6F5)2]MoCl, ([Mespyr(C6F5)2]Mo = MesitylC4H2NCH2N(CH2CH2NC6F5)2) was prepared by reaction of [Mespyr(C6F5)2]H3 with MoCl4(THF)2 and base and [Mespyr(3,5-t-Bu)2]MoCl and [Mespyr(3,5- Me)2]MoCl (3,5-t-Bu=3,5-di-tert-butylphenyl, Me = 3,5-dimethylphenyl) were synthesized likewise. All three monochlorides are paramagnetic. [Mespyr(C6F5)2]MoNMe2, [[Mespyr(otol) 2]MoNMe2, [Mespyr(3,5-t-Bu)2]MoNMe2, [Mespyr(3,5-Me)2]MoNMe2 were synthesized by reaction of the ligands with Mo(NMe2)4. The resulting compounds are diamagnetic and range in color from teal blue to emerald green. These low spin monodimethylamide complexes exist in rapid equilibria with their high spin forms. [Mespyr(C6F5)2]MoN and [Mespyr(3,5-t-Bu)2]MoN were synthesized by reaction of their respective monochlorides with NaN3 and are yellow diamagnetic species. Reaction of [Mespyr(3,5-t-Bu)2]MoN with Et3OBF4 leads to {[Mespyr(3,5- t-Bu)2]MoNEt}BF4, also a diamagnetic yellow species. [Mespyr(C6F5)2]MoOTf is synthesized by the reaction of [Mespyr(C6F5)2]MoCl with AgOTf. Reduction of [Mespyr(3,5-t-Bu)2]MoCl with Na under N2 led to [Mespyr(3,5-t-Bu)2]MoNNNa(THF)x, several species with varying numbers of THF coordination, x. A single species can be obtained when [Mespyr(3,5-t- Bu)2]MoNNNa(THF)x is reacted with either NBu4Cl or 15-crown-5 ether to yield purple green 4 {[Mespyr(3,5-t-Bu)2]MoNN}NBu4 or [Mespyr(3,5-t-Bu)2]MoNNNa(15-c-5). All the diazenide species are diamagnetic. Oxidation of the diazenide with AgOTf yields [Mespyr(3,5-t- Bu)2]Mo(N2). [Mespyr(3,5-t-Bu)2]Mo(CO) is synthesized by exposure of [Mespyr(3,5-t- Bu)2]Mo(N2) to CO. Reaction of [Mespyr(3,5-t-Bu)2]MoCl with NaBPh4 and NH3 yields {[Mespyr(3,5-t-Bu)2]Mo(NH3)}BPh4. Catalytic runs employing [Mespyr(3,5-t-Bu)2]MoN as the catalyst yielded one equivalent of NH3. A triamidoamine ligand [(HIPTNCH2CH2CH2)3N]3- was synthesized and metalated with MoCl4(THF)2 to produce [(HIPTNCH2CH2CH2)3N]MoCl ([HIPTtrpn]MoCl). Reduction of [HIPTtrpn]MoCl by KC8 under an atmosphere of dinitrogen leads to the green species [HIPTtrpn]MoNNK which can be oxidized by ZnCl2(dioxane) to produce [HIPTtrpn]Mo(N2). Other complexes synthesized include {[HIPTtrpn]Mo(NH3)}+ salts and [HIPTtrpn]Mo(CO). Xray studies were carried out on [HIPTtrpn]MoN and {[HIPTtrpn]Mo(NH3)}BAr'4. This system is not catalytic for the reduction of dinitrogen to ammonia and studies were carried out to elucidate the reasons. Oxidation studies were carried out on [HIPTN3N]Mo(N2) and [HIPTN3N]W(N2) ([HIPTN3N] = [(HIPTNCH2CH2)3N]3- ). The rate of conversion of [HIPTN3N]Mo(NH3) to [HIPTN3N]Mo(N2) was studied and found to be increased in the presence of BPh3. [HIPTN3N]Mo(N2) conversion to [HIPTN3N]Mo(CO) was found to be dependent on CO pressure. Protonation studies of [HIPTN3N]Mo(N2) were also carried out. Studies of [HIPTN3N]MoNNH decomposition showed that decomposition is not base-catalyzed. [HIPTN3N]W(CO) was synthesized by exposure of [HIPTN3N]W(N2) to CO. It is a green, paramagnetic compound and its use as a standard (for determining relative concentrations of other compounds in the IR sample) in IR spectroscopic studies appears to be promising. [HIPTN3N]MoCNH2 was synthesized by addition of acid and reducing agent to [HIPTN3N]MoCN and is a yellow, diamagnetic compound. Two triamidophosphine ligands, triHIPTamine and tri-n-Buamine were synthesized. Metalation of Zr(NMe2)4 with these ligands leads to formation of pn3HIPTZrNMe2 and pn3-n- BuZrNMe2, both diamagnetic, pale yellow complexes.
Author : Devon Charles Rosenfeld
Publisher :
ISBN 13 :
Total Pages : 402 pages
Book Rating : 4.E/5 ( download)
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:
Author : Adam Scott Hock
Publisher :
ISBN 13 :
Total Pages : 292 pages
Book Rating : 4.:/5 (156 download)
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.
Author : E.R. Braithwaite
Publisher : Elsevier
ISBN 13 : 1483290891
Total Pages : 681 pages
Book Rating : 4.4/5 (832 download)
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.
Author : Lichtenhan Joseph D.
Publisher :
ISBN 13 :
Total Pages : 168 pages
Book Rating : 4.:/5 (264 download)
Download or read book The Synthesis and Study of Molybdenum and Tungsten Silylimido and Phosphiniminato Compounds written by Lichtenhan Joseph D. and published by . This book was released on 1991 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Andrey Y. Khalimon
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (13 download)
Download or read book Molybdenum (IV) Imido Silylamido and Hydride Complexes written by Andrey Y. Khalimon and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : William R. H. Wright
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (912 download)
Download or read book Synthesis, Characterization and Reactivity of Molybdenum and Tungsten Imido Complexes of Relevance to Alkene Dimerization written by William R. H. Wright and published by . This book was released on 2009 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Therese Anne Coffey
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (594 download)
Download or read book Structural and Reactivity Studies of Bis(imido) Complexes of Molybdenum written by Therese Anne Coffey and published by . This book was released on 1998 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Mathis Benedikter
Publisher : Cuvillier Verlag
ISBN 13 : 3736963947
Total Pages : 306 pages
Book Rating : 4.7/5 (369 download)
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.
Author : Karen Yazmin Gamero-Vega
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (17 download)
Download or read book Synthesis and Reactivity Studies of Group 5 Imido and Hydrazido Complexes written by Karen Yazmin Gamero-Vega and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Keith Michael Wampler
Publisher :
ISBN 13 :
Total Pages : 260 pages
Book Rating : 4.:/5 (655 download)
Download or read book Synthetic Investigations of Molybdenum Pyrrolide and Related Complexes written by Keith Michael Wampler and published by . This book was released on 2010 with total page 260 pages. Available in PDF, EPUB and Kindle. Book excerpt: CHAPTER 1: A general introduction to olefin metathesis is given. Highlights include a historical perspective of the development of olefin metathesis and a detailed discussion of group VI imido alkylidene catalysts. CHAPTER 2: Monosiloxide and disiloxide complexes have been prepared through the addition of silanols to Mo(NR)(CHCMe 2Ph)(pyrrolyl) 2 species (R = 1 -adamantyl (Ad) or 2,6-i-Pr2C6H3 (Ar)). The silanols employed include (t-Bu)3SiOH (Hsilox), (i-Pr)3SiOH, (Me3Si)3SiOH, (t-Bu-0)3SiOH, Me2(t-Bu)SiOH, and Ph 3SiOH. The mono(silox) complex, Mo(NAr)(CHCMe 2Ph)(silox)(pyrrolyl) .(2a), could be isolated, while Mo(NAd)(CHCMe2Ph)(silox)(pyrrolyl) was observed in situ but could not be crystallized. Reaction of Mo(NAr)(CHCMe 2Ph)(OTf) 2(DME) with (silox)Li(THF) resulted in the formation of Mo(NAr)(CHCMe2Ph)(silox)(OTf) (3). Disiloxides that could be crystallized include Mo(NAd)(CHCMe 2Ph)(Silox)2 (1b), Mo(NAd)(CHCMe2Ph)[OSi(SiMe3)3]2 (5), Mo(NAd)(CHCMe 2Ph)[OSi(O-t-Bu) 3]2 (6), and Mo(NAr)(CHCMe 2Ph)[OSiMe2(t-Bu)] 2 (7); other disiloxide examples could be observed in situ, but could not be crystallized. Compound 2a reacts readily with (CF 3)Me2COH, (CF3)2MeCOH, (CF 3)2CHOH, ArOH, C6F5OH, ( - )-menthol, and ( - )-borneol to give compounds of the type Mo(NAr)(CHCMe 2Ph)(silox)(OR) (4a-g) in situ. No reaction was observed upon heating of lb under 5 atm of ethylene at 120 *C in toluene-d8 ; only at 240 'C in o-dichlorobenzene-d4 did lb react with ethylene to yield CH2=CHCMe2Ph, but the Mo-containing product could not be identified. Compound 2a reacts with ethylene at 120 'C to give Mo(NAr)(CH2)(silox)(pyr), while 4a-e react with ethylene at -60 'C; methylene species could be observed in several cases but could not be isolated. X-ray studies were carried out for lb and 2a. CHAPTER 3: Molybdenum imido alkylidene complexes which may be used as precursors for the in situ generation of molybdenum olefin metathesis catalysts are presented. Reaction of Mo(NR)(CHCMe 2Ph)(OTf)2(DME) (R = 1-adamantyl (Ad) or 2,6-i-Pr 2C6H3 (Ar)) with two equivalents of Li(ind) (ind = indolide) results in the formation of Mo(NR)(CHCMe 2Ph)(ind)2 (R = Ar, 1; Ad, 2). Unlike other molybdenum complexes of nitrogen containing heterocyclic ligands, 1 and 2 react productively with olefins. 1 and 2 react with alcohols to give previously characterized bisalkoxide olefin metathesis catalysts. Reaction of Li(3,5-R 2-pyrazolide) (R = t- Bu or Ph, R2pz) with Mo(NAr)(CHCMe 2Ph)(OTf) 2(DME) yields Mo(NAr)(CHCMe 2Ph)(3,5- R2pz)2 (R = t-Bu, 5; Ph, 6) in good yields. These complexes react with alcohols or the surface silanols of silica, to yield respectively bisalkoxy and surface monosiloxy olefin metathesis catalysts. The benzyl complexes Mo(NR)(CHCMe 2Ph)(CH2Ph)2 (R = Ar, 7; Ad, 8; Ar" = 9) have been prepared and structurally characterized. These complexes react with alcohols and phenols to give either monobenzyl monoalkoxide(aryloxide) species or trialkyl alkoxide(aryloxide) complexes. Additionally, several species that were found to not be precursors for the in situ generation of olefin metathesis catalysts are discussed. CHAPTER 4: Three substituted tris(pyrrolyl-a-methyl)amines (H3[Aryl 3TPA]) (Aryl = 2,4,6-C 6H2Me3 (Mes), la; 2,4,6-C 6H2(i-Pr)3 (Trip), 1b; 3,5-C 6H3(CF3)2 (ArF), 1c) have been prepared. An X-ray study of [Trip 3TPA]MoCl (2) shows it to be a distorted trigonal bipyramidal species in which the 2,4,6-triisopropylphenyl substituents surround and protect the apical chloride. Reaction of MoN(NMe 2)3 with H3[ArF3TPA] yields MoN(NMe2)-K3_[ArF3TPA] (3) in which only two of the ligand arms have metalated. The x-ray crystal structure revealed that the un-metalated pyrrole arm has a hydrogen bonding interaction with nitride ligand. Similarly, reaction of Mo(NMe2)4 with H3[ArF3TPA] yields Mo(NMe2)2-K3C[ArF3TPA] (3). Reaction of M(NMe 2)4 (M = Zr or Hf) with H3[ArF3TPA] results in the full metalation of the ligand to yield M(NMe2)(HNMe 2)[ArF 3TPA] (M = Zr, 5; Hf, 6), in which an equivalent of dimethylamine remains in the coordination sphere. CHAPTER 5: The monomeric, homoleptic molybdenum(III) complex molybdenum tris(2,5-dimethylpyrrolide) (1) has been prepared. Reduction with KC8 in THF yields the molybdenum(II) complex potassium [molybdenum tris(2,5-dimethylpyrrolide)] (2), while protonation with [H(OEt 2)2][BArF4] or [HNMe2Ph][B(C6F5)4] yields cationic species that contains an 9-3Hpyrrole ligand (3a and 3b). All of the complexes have been structurally characterized. The paramagnetic species have been characterized by EPR and CV. Additionally, a review of group VI pyrrolide complexes is given. APPENDIX A: The preparation and reactivity of polystyrene-supported molybdenum and tungsten imido alkylidene monoaryloxide monopyrrolide catalysts is presented. The reactivity and selectively of these complexes in the homodimerization of terminal olefins was found to be similar to their homogenous analogues. APPENDIX B: The synthesis and characterization of W(O)(CHCMe3)(Me2Pyr)2(PMe2Ph) (1), W(CCMe3)(OTf) 3(DME) (2), and [Li(OEt2)2][MoCl2(C4H3N-CH(=NAr)]) 2] (3) is described.
Author : Thomas Lucien Gianetti
Publisher :
ISBN 13 :
Total Pages : 170 pages
Book Rating : 4.:/5 (957 download)
Download or read book Synthesis and Reactivity of Reduced Niobium Imido Complexes written by Thomas Lucien Gianetti and published by . This book was released on 2014 with total page 170 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this dissertation is presented the synthesis and reactivity of Nb(III) imido complexes supported by the BDI ligand (BDI = &beta-diketimate). Chapter I. The discovery of a Nb(III)-mediated catalytic hydrogenation of internal alkynes to Z-alkenes is reported and found to proceed through an unprecedented mechanism. The mechanistic proposal involves initial reduction of the alkyne by the Nb(III) complex (BDI)Nb(NtBu)(CO)2 to provide a Nb(V) metallacyclopropene, itself capable of &sigma-bond metathesis reactivity with H2. The resulting alkenyl hydride species then undergoes reductive elimination to provide the Z-alkene product and regenerate a metal complex in the Nb(III) oxidation state. Support for the proposed mechanism is derived from i) the dependence of product selectivity on the relative concentrations of CO and H2, ii) the isolation of complexes closely related to those proposed to lie on the catalytic cycle, iii) H/D crossover experiments, and iv) DFT studies on multiple possible reaction pathways. Chapter II. Monometallic niobium arene complexes [Nb(BDI)(NtBu)(&mu-RC6H5)] (R = H and Me) were synthesized and were found to slowly converted into the diniobium inverted arene sandwich complexes [[(BDI)Nb(NtBu)]2(&mu-RC6H5)] (R = H and Me) in solution. The kinetics of this reaction were followed by 1H NMR spectroscopy, and is in agreement with a dissociative mechanism. These compounds showed a lack of reactivity towards small molecules - even at elevated temperatures - which is unusual in the chemistry of inverted sandwich complexes. However, protonation of the BDI ligands occurred readily on treatment with [H(OEt2)][B(C6F5)4], resulting in the mono-protonated cationic inverted sandwich complex [[(BDI#)Nb(NtBu)][(BDI)Nb(NtBu)](&mu-C6H5)][B(C6F5)4] and the dicationic complex [[(BDI#)Nb(NtBu)]2(&mu-RC6H5)][B(C6F5)4]2 (BDI# = (ArNC(Me))2CH2). NMR and UV-vis spectroscopies were used to characterize this unique series of diamagnetic molecules as a means of determining how best to describe the Nb-arene interactions. The X-ray crystal structures, UV-visible spectra, arene 1H NMR chemical shifts and large JCH coupling constants provide evidence for donation of electron density from the Nb d-orbitals into the antibonding [pi] system of the arene ligands. However, the lack of sp3 hybridization of the arene carbon indicate that the Nb-arene donation is not accompanied by an increase in formal oxidation state, and suggest that 4d2 electronic configurations are appropriate to describe the Nb atoms in all four complexes. Chapter III. Inverted sandwich complexes have seen interesting recent developments both in the nature of their bonding and in their use as chemical reactants. Although discussions concerning the electronic delocalization lend credit to their use as potential electronic and spintronic devices, mixed valent inverted sandwich complexes are rarely reported. We show in this work that the selective single electron oxidation of a neutral benzene inverted sandwich complex of niobium leads to an isolable cationic mixed valent benzene inverted sandwich complex. The latter complex shows unique structural features elucidated through studies with an arsenal of physical methods, including cyclic voltammetry, 1H NMR, UV-Vis, magnetism, EPR spectroscopies, in addition to DFT calculations. These analyses indicate that although delocalization is allowed over the benzene ring from both niobium atoms, the single electron is unequally shared between the two metal centres. Under certain conditions, this complex reforms the neutral benzene complex along with a highly reactive Nb(IV) species, which is of great interest for potential chemical reactivity. Chapter IV. All three C-F bonds in CF3-substituted arenes are activated by a niobium imido complex, driven by the formation of strong Nb-F bonds. The mechanism of this transformation was studied by NMR spectroscopy which revealed the involvement of Nb(III). Attempts to extend this chemistry to non-aromatic CF3 groups led to intramolecular reactivity.The mechanism of activation of C-F bonds in fluoroarenes using a well-defined niobium (III) imido complex has been investigated. Chapter V. The Nb(III) arene species [BDI]Nb(NtBu)(C6H6), reacts stoichiometrically with fluoroarenes to yield niobium (V) aryl fluorides. Spectroscopic analysis supported by DFT calculations revealed the critical involvement of a Nb(III) fluoroarene-bound species. In contrast to previous reports of related reactivity, we found that perfluorinated arenes (i.e. those normally assumed to bear more `activated' C-F bonds) are, in the present system, much less reactive towards C-F bond cleavage than mono- or difluoro-substituted arenes. In addition to demonstrating stoichiometric hydrodefluorination reactions, we also describe an efficient and mild hydrodefluorination of mono- and di-fluoroarenes that is catalytic in niobium.
Author : Betty A. Ooro
Publisher :
ISBN 13 :
Total Pages : 216 pages
Book Rating : 4.:/5 (613 download)
Download or read book Synthesis, Characterization and Reactivity Studies of Hexanuclear Molybdenum Cluster Complexes written by Betty A. Ooro and published by . This book was released on 2004 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Laughlin G. McCullough
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ISBN 13 :
Total Pages : 282 pages
Book Rating : 4.:/5 (121 download)
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:
Author : John Stephen Murdzek
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ISBN 13 :
Total Pages : 1082 pages
Book Rating : 4.:/5 (199 download)
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:
