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LDRD final report on new homogeneous catalysts for direct olefin epoxidation (LDRD 52591).

Description: This report summarizes our findings during the study of a novel homogeneous epoxidation catalyst system that uses molecular oxygen as the oxidant, a ''Holy Grail'' in catalysis. While olefins (alkenes) that do not contain allylic hydrogens can be epoxidized directly using heterogeneous catalysts, most olefins cannot, and so a general, atom-efficient route is desired. While most of the work performed on this LDRD has been on pincer complexes of late transition metals, we also scouted out metal/ligand combinations that were significantly different, and unfortunately, less successful. Most of the work reported here deals with phosphorus-ligated Pd hydrides [(PCP)Pd-H]. We have demonstrated that molecular oxygen gas can insert into the Pd-H bond, giving a structurally characterized Pd-OOH species. This species reacts with oxygen acceptors such as olefins to donate an oxygen atom, although in various levels of selectivity, and to generate a [(PCP)Pd-OH] molecule. We discovered that the active [(PCP)Pd-H] active catalyst can be regenerated by addition of either CO or hydrogen. The demonstration of each step of the catalytic cycle is quite significant. Extensions to the pincer-Pd chemistry by attaching a fluorinated tail to the pincer designed to be used in solvents with higher oxygen solubilities are also presented.
Date: February 1, 2006
Creator: Goldberg, Karen (University of Washington); Smythe, Nicole A. (University of Washington); Moore, Joshua T.; Stewart, Constantine A.; Kemp, Richard Alan; Miller, James Edward et al.
Partner: UNT Libraries Government Documents Department

Electrophilic metal alkyl chemistry in new ligand environments

Description: Cationic group 4 and actinide Cp{sub 2}MR{sup +} metallocenes, and isolobal neutral group 3 and lanthanide Cp{sub 2}MR analogs, are exceptionally reactive in insertion and {sigma}-bond metathesis processes, and have been exploited extensively in catalysis and synthesis, most notably single-site olefin polymerization. The objectives of recent work were to design new electrophilic metal alkyls based on non-Cp{sub 2}M structures, and to exploit these systems in fundamental and applied studies related to olefin polymerization and other catalytic reactions. Key results are reported in the following areas: discrete non-metallocene cationic group 4 alkyls, activation of non-metallocene compounds with methylalumoxane, and cationic aluminum alkyl compounds. Numerous structural formulas are included.
Date: September 11, 2002
Creator: Jordan, Richard F.
Partner: UNT Libraries Government Documents Department

Asymmetric Intramolecular Alkylation of Chiral Aromatic Imines via Catalytic C-H Bond Activation

Description: The asymmetric intramolecular alkylation of chiral aromatic aldimines, in which differentially substituted alkenes are tethered meta to the imine, was investigated. High enantioselectivities were obtained for imines prepared from aminoindane derivatives, which function as directing groups for the rhodium-catalyzed C-H bond activation. Initial demonstration of catalytic asymmetric intramolecular alkylation also was achieved by employing a sterically hindered achiral imine substrate and catalytic amounts of a chiral amine.
Date: April 16, 2007
Creator: Watzke, Anja; Wilson, Rebecca; O'Malley, Steven; Bergman, Robert & Ellman, Jonathan
Partner: UNT Libraries Government Documents Department

Asymmetric Synthesis of (-)-Incarvillateine Employing an Intramolecular Alkylation via Rh-Catalyzed Olefinic C-H Bond Activation

Description: An asymmetric total synthesis of (-)-incarvillateine, a natural product having potent analgesic properties, has been achieved in 11 steps and 15.4% overall yield. The key step is a rhodium-catalyzed intramolecular alkylation of an olefinic C-H bond to set two stereocenters. Additionally, this transformation produces an exocyclic, tetrasubstituted alkene through which the bicyclic piperidine moiety can readily be accessed.
Date: February 18, 2008
Creator: Tsai, Andy; Bergman, Robert & Ellman, Jonathan
Partner: UNT Libraries Government Documents Department

A Well-Defined, Silica-Supported Tungsten Imido Alkylidene OlefinMetathesis Catalyst

Description: The reaction of [W(=NAr)(=CHtBu)(CH2tBu)2](1; Ar =2,6-iPrC6H3) with a silica partially dehydroxylated at 700oC, SiO2-(700),gives syn-[(_SiO)W(=NAr)(=CHtBu)(CH2tBu)](2) as a major surface species,which was fully characterized by mass balance analysis, IR, NMR, EXAFS,and DFT periodic calculations. Similarly, complex 1 reacts with[(c-C5H9)7Si7O12SiOH]to give [(SiO)W(=NAr)(=CHtBu)(CH2tBu)](2m), whichshows similar spectroscopic properties. Surface complex 2 is a highlyactive propene metathesis catalyst, which can achieve a TON of 16000within 100 h, with only a slow deactivation.
Date: June 13, 2006
Creator: Rhers, Bochra; Salameh, Alain; Baudouin, Anne; Quadrelli, ElsjeA.; Taoufik, Mostafa; Coperet, Christophe et al.
Partner: UNT Libraries Government Documents Department

Enantioselective Intramolecular Hydroarylation of Alkenes via Directed C-H Bond Activation

Description: Highly enantioselective catalytic intramolecular ortho-alkylation of aromatic imines containing alkenyl groups tethered at the meta position relative to the imine directing group has been achieved using [RhCl(coe){sub 2}]{sub 2} and chiral phosphoramidite ligands. Cyclization of substrates containing 1,1- and 1,2-disubstituted as well as trisubstituted alkenes were achieved with enantioselectivities >90% ee for each substrate class. Cyclization of substrates with Z-alkene isomers proceeded much more efficiently than substrates with E-alkene isomers. This further enabled the highly stereoselective intramolecular alkylation of certain substrates containing Z/E-alkene mixtures via a Rh-catalyzed alkene isomerization with preferential cyclization of the Z-isomer.
Date: May 22, 2008
Creator: Harada, Hitoshi; Thalji, Reema; Bergman, Robert & Ellman, Jonathan
Partner: UNT Libraries Government Documents Department


Description: "Ultrasene" typically contained 57 wt % branched paraffins and cycloparaffins, 40 wt% n-paraffins, 3 wt% aromatics, and less than 0.1 wt% olefins. The n-paraffinic fraction from "Ultrasene" was stable to chemical and radiolytic degradation, whereas the combined branched paraffinic and cycloparaffinic fraction, and the aromatic fraction, were significantly less stable. (auth)
Date: June 1, 1961
Creator: West, D. L.
Partner: UNT Libraries Government Documents Department

Low Severity Coal Liquefaction Promoted by Cyclic Olefins

Description: The development of the donor solvent technology for coal liquefaction has drawn a good deal of attention over the last three decades. The search for better hydrogen donors led investigators to a class of compounds known as cyclic olefins. Cyclic olefins are analogues of the conventional hydroaromatic donor species but do not contain aromatic rings. The cyclic olefins are highly reactive compounds which readily release their hydrogen at temperatures of 200 C or higher. Considerable effort has been o expended toward understanding the process of hydrogen donation. Most of this work was conducted in bomb reactors, with product analysis being carried out after the reaction was complete. Efforts directed towards fundamental studies of these reactions in situ are rare. The current work employs a high temperature and high pressure infrared cell to monitor in situ the concentrations of reactants and products during hydrogen release from hydrogen donor compounds.
Date: April 9, 1998
Creator: Curtis, Christine W.
Partner: UNT Libraries Government Documents Department

A description of NUEXS, an upgrade of the code FCUP used to compute proton recoil current from CH{sub 2} foils

Description: A computer code, FCUP, developed by A. Craft computes currents of recoil protons from a time- and energy-dependent neutron flux striking a CH{sub 2} foil. Three problem areas need to be addressed to extend the code`s usefulness. First, FCUP computes a response that is not time dependent; that is, only the input time bin is broadened to account for the finite time distribution of protons from a single neutron energy; second, the time coordinate of the signal predicted is translated arbitrarily rather than absolutely relative to the time of maximum neutron production in the source; and third, the code does not account for electron pickup by protons at low proton energies in the target and absorber foils. This report describes the changes in calculational method used to overcome these problems.
Date: August 1, 1982
Creator: Stelts, M.L. & Wood, B.E.
Partner: UNT Libraries Government Documents Department

[Energies of organic compounds]

Description: The enthalpy of reduction of lactones to the corresponding diols has been determined, allowing the enthaipies of formation of the lactones to be determined. Results of this study agree well with data obtained for enthalpies of hydrolysis of the lactones. We have begun the measurement of the enthalpies of reduction of norbornanones, and we have shown that it is possible to determine the difference in energy between the exo and endo forms of the product alcohols by measuring the equilibrium constant as a function of temperature. The study of the enthalpies of hydration of carbonyl compounds has continued, and the enthalpies of hydrolysis of the corresponding ketals is being determined. The study of the enthalpies of hydration of alkenes is nearly completed, and the rearrangement reactions which were uncovered are being investigated.
Date: December 31, 1991
Creator: Wiberg, K.B.
Partner: UNT Libraries Government Documents Department

The mechanism for iron-catalyzed alkene isomerization in solution

Description: Here we report nano- through microsecond time-resolved IR experiments of iron-catalyzed alkene isomerization in room-temperature solution. We have monitored the photochemistry of a model system, Fe(CO){sub 4}({eta}{sup 2}-1-hexene), in neat 1-hexene solution. UV-photolysis of the starting material leads to the dissociation of a single CO to form Fe(CO){sub 3}({eta}{sup 2}-1-hexene), in a singlet spin state. This CO loss complex shows a dramatic selectivity to form an allyl hydride, HFe(CO){sub 3}({eta}{sup 3}-C{sub 6}H{sub 11}), via an internal C-H bond-cleavage reaction in 5-25 ns. We find no evidence for the coordination of an alkene molecule from the bath to the CO loss complex, but do observe coordination to the allyl hydride, indicating that it is the key intermediate in the isomerization mechanism. Coordination of the alkene ligand to the allyl hydride leads to the formation of the bis-alkene isomers, Fe(CO){sub 3}({eta}{sup 2}-1-hexene)({eta}{sup 2}-2-hexene) and Fe(CO){sub 3}({eta}{sup 2}-1-hexene){sub 2}. Because of the thermodynamic stability of Fe(CO){sub 3}({eta}{sup 2}-1-hexene)({eta}{sup 2}-2-hexene) over Fe(CO){sub 3}({eta}{sup 2}-1-hexene){sub 2} (ca. 12 kcal/mol), nearly 100% of the alkene population will be 2-alkene. The results presented herein provide the first direct evidence for this mechanism in solution and suggest modifications to the currently accepted mechanism.
Date: May 27, 2008
Creator: Sawyer, Karma R.; Glascoe, Elizabeth A.; Cahoon, James F.; Schlegel, Jacob P. & Harris, Charles B.
Partner: UNT Libraries Government Documents Department


Description: Selective occlusions of straight-chain paraffins in the presence of branched-chain hydrocarbons by naturally occurring zeolites of suitable dimension was reported as early as 1944 by Barrer and Ibbitson. More recently the capacity of synthetic zeolites or molecular sieves to absorb exclusively the straight-chain hydrocarbons from complex hydrocarbon mixtures has found extensive application in the petroleum industry. Under the conditions developed for most sieving operations any normal olefins present are occluded along with the normal paraffins. A supplemental separation technique must be employed to obtain n-paraffins free of olefins.
Date: August 30, 1966
Creator: Fenselau, Catherine & Calvin, Melvin
Partner: UNT Libraries Government Documents Department


Description: The synthesis of nonracemic yields of hexa-, hepta-, octa-, and nonhelicene with circular light was observed, and the structural and wavelength dependence of the induced optical yields was examined. The results obtained, together with a detailed consideration of the mechanism of helicene synthesis from the parent diarylolefins, indicate that the induced optical activity is due to selective reaction of enantiomeric conformations of the parent cis diarylolefins by circular light.
Date: May 1, 1971
Creator: Bernstein, William J.; Calvin, Melvin & Buchardt, Ole.
Partner: UNT Libraries Government Documents Department

Stopping the growth of particles to silica-supported mono-nuclear Ru hydride surface species by tuning silica with surface silanes

Description: Tuning silica by replacing surface silanols with silanes allows chemical grafting of Ru(COD)(COT) through a covalent Ru-Si bond, as evidenced by elemental analysis, IR spectroscopy and EXAFS. Treatment of these surface species under H2 at 300 oC yields a mononuclear Ru hydride species, without any sintering of the metal according to TEM and EXAFS analyses. This supported system displays catalytic properties different from those of supported Ru particles (2 nm), selectively hydrogenating olefins over aromatics.
Date: July 11, 2007
Creator: Berthoud, Romain; Fenet, Bernard; Lukens, Wayne; Pelzer, Katrin; Basset, Jean-Marie; Candy, Jean-Pierre et al.
Partner: UNT Libraries Government Documents Department

CH3-ReO3 on gamma-Al2O3: understanding its structure, initiation,and reactivity in olefin metathesis

Description: Me-ReO3 on gamma-alumina: understanding the structure, theinitiation and thereactivity of a highly active olefin metathesiscatalyst Heterolytic splitting of the C-H bond of the methyl group ofCH3ReO3 on AlsO reactive sites of alumina as a way to generate the activesite of CH3ReO3 supported on gamma-Al203.
Date: January 20, 2007
Creator: Salameh, Alain; Joubert, Jerome; Baudouin, Anne; Lukens, Wayne; Delbecq, Francoise; Sautet, Philippe et al.
Partner: UNT Libraries Government Documents Department


Description: The tendency of various classes of pure hydrocarbons to form zirconium- complexing ligands during chemical or radiolytic degradation was evaluated. Olefins and aromaticcycloparaffins (mixed type) formed the most ligands and normal paraffins the fewest. (auth)
Date: April 1, 1961
Creator: Dennis, B.P.
Partner: UNT Libraries Government Documents Department


Description: Using a reactor in which the coal is physically separated from the solid catalyst by a porous wall permeable to the hydrogen donor solvent, it was shown that direct contact between the catalyst and the coal is not required for catalyzed coal liquefaction. This occurs however only when there is a hydrogen atmosphere, as liquefaction with catalyst participation does not occur in a nitrogen atmosphere. Liquefaction by hydrogen transfer from the donor solvent itself does occur. This suggests that there is transfer of hydrogen from the catalyst to the coal via the solvent. The character of the solvent makes a significant difference, the better solvents being good hydrogen donors. These results indicate that the role of the catalyst may be to regenerate the spent hydrogen donor solvent during the liquefaction process. The peak temperature for volatiles evolution has been shown to be a reproducible measure of the coal rank. This was shown by an excellent correlation (R2 = 0.998) between peak volatiles temperatures (by TGA) and vitrinite reflectance. Using TG/MS, the volatiles contents of coals of a wide range of ranks was determined. The low rank coals emit largely phenols and some other oxygen compounds and olefins. The higher rank coals emit largely aromatic hydrocarbons and some olefins.
Date: January 1, 2000
Creator: Klein, Michael T.
Partner: UNT Libraries Government Documents Department

[Energies of organic compounds]

Description: The first part of our study of the enthalpy of reduction of carbonyl compounds has been completed and includes four aldehydes, acetone, a series of cyclic ketones and ethyl acetate. Results suggest that some of the literature data for these compounds are significantly in error. Equilibrium constants have been measured for the reaction of carbonyl compounds with water to give hydrates as well as with methanol to give either hemiacetals or acetals. They cover a wide range, and studies are underway to determine the reasons for the differences. Studies of the enthalpies of hydration of some alkenes which yield tertiary alcohols have been completed, as well as a study of the hydrolysis of lactones. The ``gauche effect`` has been studied, and has been shown to result from the formation of bent bonds when atoms of much different electronegativity are joined.
Date: July 1, 1995
Partner: UNT Libraries Government Documents Department

Separating Mechanical and Chemical Contributions to Molecular-Level Friction

Description: The authors use force-probe microscopy to study the friction force and the adhesive interaction for molecular monolayer self-assembled on both Au probe tips and substrate surfaces. By systematically varying the chemical nature of the end groups on these monolayers the authors have, for the first time, delineated the mechanical and chemical origins of molecular-level friction. They use chemically inert {double_bond}CH{sub 3} groups on both interracial surfaces to establish the purely mechanical component of the friction and contrast the results with the findings for chemically active {double_bond}COOH end-groups. In addition, by using odd or even numbers of methylene groups in the alkyl backbones of the molecules they are able to determine the levels of inter-film and intra-film hydrogen bonding.
Date: August 14, 2000
Partner: UNT Libraries Government Documents Department