Investigations of Pincer-ligated Transition Metal Complexes for the Activation of Molecular Oxygen PDF Download

Author: Brian Joseph Boro
Publisher:
ISBN:
Category : Alkenes
Languages : en
Pages : 250

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Author: Wilson D. Bailey
Publisher:
ISBN:
Category : Alkenes
Languages : en
Pages : 181

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Late transition-metal pincer complexes of primarily palladium(II) and platinum(II) have been investigated for their application as catalysts in partial oxidation reactions. The epoxidation of higher olefins using molecular oxygen as the oxidant has been targeted, and the individual reaction steps needed to accomplish this overall transformation are described herein, including: (1) hydrogenolysis of a metal hydroxide (M-OH) species to yield a metal hydride (M-H), (2) insertion of O2 into the M-H bond to form a metal hydroperoxide (M-OOH), and (3) O-atom transfer from the M-OOH to epoxides, yielding a M-OH and completing the catalytic cycle. Previous results from our group on these individual transformations using (tBuPCP)Pd and (tBuPCO)Pd fragments are also reviewed. The requirements for O2 insertion into PdII and PtII hydrides are discussed. An array of cationic, neutral, and anionic Pd-H and Pt-H complexes supported by a tBuPNP backbone were synthesized and evaluated for O2 insertion (tBuPNP = 2,6-bis-(di-tbutylphosphinomethyl)pyridine). Metal-ligand cooperation was observed in the activation of H2 to form neutral hydride complexes. The effect of ligand protonation/deprotonation on the trans influence experienced by the hydride ligand was investigated. No reaction with O2 was observed with the cationic hydrides, while the neutral and anionic forms reacted with O2 at the tBuPNP backbone. The synthesis and characterization of mono- and dinuclear Pd-OH complexes supported by a PCNR pincer ligand (PCNR = (1-(3-((di-tert-butylphosphino)methyl)phenyl)-1H-5-R-pyrazole), R = H, Me) is presented. When R = H, ligand pyrazole "rollover" C-H activation was observed, forming a mixed ligand (PCNH)Pd(μ-OH)Pd(PCC) dinuclear structure. This "rollover" was investigated using DFT computations. The mono- and dinuclear hydroxide species were evaluated for hydrogenolysis. The dinuclear compounds {[(PCNR)Pd]2(μ-OH)}[OTf] reacted under an H2 atmosphere to yield the corresponding dinuclear hydrides {[(PCNR)Pd]2(μ-H)}[OTf]. A mechanistic study on the hydrogenolysis of the μ-bridged hydroxide {[(PCNMe)Pd]2(μ-OH)}[OTf] revealed first order kinetics in both [Pd] and [H2]. Terminal hydrides were not detected, and reduction of the mononuclear hydroxide complexes (PCNR)Pd-OH to Pd0 was observed under H2. The reduction was proposed to proceed through displacement of the pyrazole arm, and was examined by DFT computations. Lastly, a new strategy to promote O-atom transfer from M-OOH to epoxides, the final step in the targeted catalytic cycle, is proposed. Preliminary studies on NNNPyz, NNNEt, and NNMe ligated PdII and PtII are discussed (NNNPyz = 2,6-bis(5-tbutyl-1H-pyrazol-3-yl)pyridine; NNNEt = 2-(5-tbutyl-1H-pyrazol-3-yl)-6-(diethylaminomethyl)pyridine; NNMe = 2-(5-tBu-1H-pyrazol-3-yl)-6-methylpyridine). The NNNPyz ligand, containing two acidic sites in proximity to the fourth site in the square plane, was found to protonate M-O2 complexes, chelate to the metal center and oxidize phosphine substrates. Similar reactivity was observed with NNNEt and NNMe, however hemilability of these ligands resulted in undesired coordination modes.

Author: Arthur Martell
Publisher: Springer Science & Business Media
ISBN: 1461309557
Category : Science
Languages : en
Pages : 341

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This monograph consists of manuscripts, summary statements, and poster abstracts submitted by invited speakers and poster contributors who participated in the symposium "Oxygen Complexes and Oxygen Activation by Transition Metals," held March 23-26, 1987, at Texas A&M University. This meeting was the fifth annual international symposium sponsored by the Texas A&M Industry-University Cooperative Chemistry Program (IUCCP). The co chairmen of the conference were Professors Arthur E. Martell and Donald T. Sawyer of the Texas A&M University Chemistry Department. The program was developed by an academic-industrial steering committee consisting of the co-chairmen and members appointed by the sponsoring chemical companies Dr. James F. Bradzil, The Standard Oil Company, Ohio; Dr. Jerry R. Ebner, Monsanto Company; Dr. Craig Murchison, Dow Chemical Company; Dr. Donald C. Olsen, Shell Development Company; Dr. Tim R. Ryan, Celanese Chemical Company; and Dr. Ron Sanderson, Texaco Chemical Company. The subject of this conference reflects the intense interest that has developed in academic institutions and industry on several aspects of dioxygen chemistry. These include the formation of dioxygen complexes and their applications in facilitated transport and oxygen separation; homo geneous and heterogeneous catalysis of oxidation; and oxygenation of organic substrates by molecular oxygen. The conference differs in two respects from several other symposia on dioxygen chemistry held during the past few years. First, there is extensive industrial participation, especially with respect to oxygen activation.

Author: David Morales-Morales
Publisher: Elsevier
ISBN: 0128129328
Category : Science
Languages : en
Pages : 756

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Pincer Compounds: Chemistry and Applications offers valuable state-of-the-art coverage highlighting highly active areas of research—from mechanistic work to synthesis and characterization. The book focuses on small molecule activation chemistry (particularly H2 and hydrogenation), earth abundant metals (such as Fe), actinides, carbene-pincers, chiral catalysis, and alternative solvent usage. The book covers the current state of the field, featuring chapters from renowned contributors, covering four continents and ranging from still-active pioneers to new names emerging as creative strong contributors to this fascinating and promising area. Over a decade since the publication of Morales-Morales and Jensen’s The Chemistry of Pincer Compounds (Elsevier 2007), research in this unique area has flourished, finding a plethora of applications in almost every single branch of chemistry—from their traditional application as very robust and active catalysts all the way to potential biological and pharmaceutical applications. Describes the chemistry and applications of this important class of organometallic and coordination compounds Includes contributions from global leaders in the field, featuring pioneers in the area as well as emerging experts conducting exciting research on pincer complexes Highlights areas of promising and active research, including small molecule activation, earth abundant metals, and actinide chemistry

Author: Kálmán J. Szabó
Publisher: John Wiley & Sons
ISBN: 3527681337
Category : Science
Languages : en
Pages : 389

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This new book on this hot topic summarizes the key achievements for the synthesis and catalytic applications of pincer and pincer-type complexes, providing readers with the latest research highlights. The editors have assembled an international team of leaders in the field, and their contributions focus on the application of various pincer complexes in modern organic synthesis and catalysis, such as C-C and C-X bond forming reactions, C-H bond functionalization, and the activation of small molecules, as well as asymmetric catalysis. A must-have for every synthetic chemist in both academia and industry intending to develop new catalysts and improved synthetic protocols.

Author: Kenneth John Balkus
Publisher:
ISBN:
Category : Oxygen
Languages : en
Pages : 630

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The research reported in Chapters I-IV involves the synthesis and spectroscopic characterization of synthetic 2 and CO carriers, improvement of the stability and reversibility of these metal dioxygen and carbonyl complexes by varying the supports and ligand environment, and the incorporation of these complexes in polystyrene membranes as part of a novel gas separation process. Bi s (salicylidene-Y-iminopropyl) methylaminoco bait (II) and derivations thereof, supported on both polystyrene and silica which bind O2 reversibly in the solid state, are described in detail. The characterization of a novel zeolite encapsulated anionic complex is also reported. This compound, proposed to be Co(CN)Y, binds dioxygen reversibly, at least 400 cycles and is stable to moisture. Several new Cu(ll) complexes supported on polystyrene were prepared and their reversible interaction with carbon monoxide was investigated. A new method for the separation of oxygen from air is presented. The system involves the incorporation of supported transition metal complexes that reversibly bind dioxygen into polystyrene membranes in order to facilitate the transport of O2. These films, subsequently employed in a closed volume experiment, exhibited enhanced 2 permselectivity . The permeation apparatus, experimental procedure and membrane characterization are presented in detail. A mechanism of transport which involves a site to site interaction between metal centers is discussed. The work in Chapter V focuses on employing lacunary heteropolyanions (HPAs) as oxidatively resistant ligands for catalytically active metal ions. The reactivity in organic solvents of CXMW 1 ^39"", where M = Co(II), Mn(ll) and Fe(III), was investigated. In the presence of alkyl peroxide or iodosylbenzene, these HPAs were found to catalyze the oxidation of several organic substrates. This research led to the discovery of a dirhodium heteropolytungstate catalyst. This polyoxometallate is proposed to be a metal-metal bonded Rh 2 substituted Keggin ion. The preparation and characterization of this compound are described in detail. The RhHPA was found to be an effective catalyst for the allylic oxidation of cyclic olefins by molecular On. Unusual selectivity for the production of the a, g- unsaturated carbonyl was observed. A consideration of the general features of this reaction led to a proposed mechanism which involves an ion free radical decomposition of insitu generated peroxides.

Author: Arthur Martell
Publisher:
ISBN: 9781461309567
Category :
Languages : en
Pages : 356

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Author: Walter Kaminsky
Publisher: Wiley-VCH
ISBN: 9783527317424
Category : Technology & Engineering
Languages : en
Pages : 0

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With an enormous velocity, olefin polymerization has expanded to one of the most significant fields in polymers since the first industrial use about 50 years ago. In 2005, 100 million tons of polyolefins were produced - the biggest part was catalyzed by metallorganic compounds. The Hamburg Macromolecular Symposium 2005 with the title "Olefin Polymerization" involved topics such as new catalysts and cocatalysts, kinetics, mechanism and polymer reaction engineering, synthesis of special polymers, and characterization of polyolefins. The conference combined scientists from different disciplines to discuss latest research results of polymers and to offer each other the possibility of cooperation. This is reflected in this volume, which contains invited lectures and selected posters presented at the symposium.

Author: Paul Michael Geoghegan
Publisher:
ISBN:
Category : Ligands
Languages : en
Pages : 120

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Author: Karen I. Goldberg
Publisher: ACS Symposium
ISBN: 9780841238497
Category : Science
Languages : en
Pages : 0

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Activation and Functionalization of C-H Bonds explores recent developments in the reaction chemistry of solution-phase transition-metal based systems with simple hydrocarbons and with more complex organic molecules. More than 20 internationally leading research groups contributed to this volume, and their chapters cover such topics as fundamental theoretical and mechanistic studies of C-H bond activation by metal complexes, catalytic systems for alkane functionalization, and new applications in synthetic organic chemistry. An introductory chapter offers an overview of stoichiometric and catalytic reactions of C-H bonds with transition metal complexes. The C-H bond is the most widespread linkage in organic chemistry, present in virtually every organic molecule. Unfortunately, C-H bonds are famously resistant to selective chemical transformations. The development of methods for their selective transformations has enormous potential value in fields ranging from the chemistry of fuels (for example, the conversion of methane to methanol) to the synthesis of the most complex organic molecules.