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Synthesis of a Benzodiazepine-derived Rhodium NHC Complex by C-H Bond Activation

Description: The synthesis and characterization of a Rh(I)-NHC complex generated by C-H activation of 1,4-benzodiazepine heterocycle are reported. This complex constitutes a rare example of a carbene tautomer of a 1,4-benzodiazepine aldimine stabilized by transition metal coordination and demonstrates the ability of the catalytically relevant RhCl(PCy{sub 3}){sub 2} fragment to induce NHC-forming tautomerization of heterocycles possessing a single carbene-stabilizing heteroatom. Implications for the synthesis of benzodiazepines and related pharmacophores via C-H functionalization are discussed.
Date: January 30, 2008
Creator: Bergman, Roberg G.; Gribble, Jr., Michael W. & Ellman, Jonathan A.
Partner: UNT Libraries Government Documents Department

N-Heterocyclic Carbenes of the Late Transition Metals: A Computational and Structural Database Study

Description: A computational chemistry analysis combined with a crystallographic database study of the bonding in late transition metal N-heterocyclic carbene (NHC) complexes is reported. The results illustrate a metal-carbon bond for these complexes, approximately 4% shorter than that of a M-C single bond found in metal alkyl complexes. As a consequence of this result, two hypotheses are investigated. The first hypothesis explores the possibility of multiple-bond character in the metal-carbon linkage of the NHC complex, and the second, considers the change in the hybridization of the carbenoid carbon to incorporate more p character. The latter hypothesis is supported by the results. Analysis of these complexes using the natural bond orbital method evinces NHC ligands possessing trans influence.
Date: May 2005
Creator: Baba, Eduard
Partner: UNT Libraries

Fundamental spectroscopic studies of carbenes and hydrocarbon radicals

Description: Determination of bond dissociation energies and heats of formation of hydrocarbon radicals and carbenes requires knowledge of their structures, but this is not provided by standard mass spectrometric studies; what is needed is high-resolution spectroscopy, often best achieved at centimeter and millimeter wavelengths. Nearly 60 reactive organic molecules were investigated in the period from 1988--1998.
Date: March 12, 1999
Partner: UNT Libraries Government Documents Department

Investigation of organometallic reaction mechanisms with one and two dimensional vibrational spectroscopy

Description: One and two dimensional time-resolved vibrational spectroscopy has been used to investigate the elementary reactions of several prototypical organometallic complexes in room temperature solution. The electron transfer and ligand substitution reactions of photogenerated 17-electron organometallic radicals CpW(CO){sub 3} and CpFe(CO){sub 2} have been examined with one dimensional spectroscopy on the picosecond through microsecond time-scales, revealing the importance of caging effects and odd-electron intermediates in these reactions. Similarly, an investigation of the photophysics of the simple Fischer carbene complex Cr(CO){sub 5}[CMe(OMe)] showed that this class of molecule undergoes an unusual molecular rearrangement on the picosecond time-scale, briefly forming a metal-ketene complex. Although time-resolved spectroscopy has long been used for these types of photoinitiated reactions, the advent of two dimensional vibrational spectroscopy (2D-IR) opens the possibility to examine the ultrafast dynamics of molecules under thermal equilibrium conditions. Using this method, the picosecond fluxional rearrangements of the model metal carbonyl Fe(CO){sub 5} have been examined, revealing the mechanism, time-scale, and transition state of the fluxional reaction. The success of this experiment demonstrates that 2D-IR is a powerful technique to examine the thermally-driven, ultrafast rearrangements of organometallic molecules in solution.
Date: December 16, 2008
Creator: Cahoon, James Francis
Partner: UNT Libraries Government Documents Department

Synthesis and Gas Phase Thermochemistry of Germanium-Containing Compounds

Description: The driving force behind much of the work in this dissertation was to gain further understanding of the unique olefin to carbene isomerization observed in the thermolysis of 1,1-dimethyl-2-methylenesilacyclobutane by finding new examples of it in other silicon and germanium compounds. This lead to the examination of a novel phenylmethylenesilacyclobut-2-ene, which did not undergo olefin to carbene rearrangement. A synthetic route to methylenegermacyclobutanes was developed, but the methylenegermacyclobutane system exhibited kinetic instability, making the study of the system difficult. In any case the germanium system decomposed through a complex mechanism which may not include olefin to carbene isomerization. However, this work lead to the study of the gas phase thermochemistry of a series of dialkylgermylene precursors in order to better understand the mechanism of the thermal decomposition of dialkylgermylenes. The resulting dialkylgermylenes were found to undergo a reversible intramolecular {beta} C-H insertion mechanism.
Date: December 31, 2002
Creator: Classen, Nathan Robert
Partner: UNT Libraries Government Documents Department

Synthetic and Thermodynamic Investigations of Ancillary Ligand Influence on Catalytic Organometallic Systems. Final Report

Description: During the grant period we have been involved in synthesizing and experimentally determining solution enthalpy values associated with partially fluorinated ligands. This has lead to the publication of manuscripts dealing with synthetic, calorimetric and catalytic behavior of partially fluorinated ligands. The collaboration with Los Alamos researchers has lead to the publication of catalytic results in sc CO{sub 2} which have proven very interesting. Furthermore, we have also examined ligands that behave as phosphine mimics. The N-heterocyclic carbenes have been explored as alternatives for tertiary phosphines and have resulted in the design and construction of efficient palladium and nickel system capable of performing C-C and C-N cross coupling reactions. The initial studies in this areas were made possible by exploratory work conducted under the DOE/EPSCoR grant.
Date: March 20, 2003
Creator: Nolan, Steven
Partner: UNT Libraries Government Documents Department

Bond forming reactions of carbyne and nitrene complexes. Final technical report for DE-FG02-96ER14608

Description: An isolobal relationship among terminal carbyne, nitrene and oxo ligands provided the basis for our efforts to explore new synthetic routes to such complexes and to probe bond forming reactions of these ligands. The specific goals of this project were to explore reactions of carbyne and nitrene ligands, and a summary of our results follows. Manipulation of metal-ligand pi bonds to control reactivity patterns provided the conceptual basis for this work. New transformations and coupling reactions of the CR and NR moieties bound to metal centers have been explored and transformations of carbyne or nitrene ligands have been achieved. Perhaps the most exciting results have come in the area of the simplest ligand: the CH carbyne unit. Treatment of [Tp'(CO){sub 2}W{triple_bond}C-PPh{sub 3}] [PF{sub 6}] Tp' = hydridotris(3,5-dimethylpyrazolylborate) with Na[HBEt{sub 3}] forms the methylidyne complex Tp' (CO){sub 2}W{triple_bond}C-H via formyl and carbene intermediates. Protonation of the Tp'(CO){sub 2}W{triple_bond}C-H methylidyne complex yields the cationic agostic methylidene complex, [Tp'(CO){sub 2}W=CH{sub 2}][BF{sub 4}]. The methylidyne complex with a pK{sub a} of 28.7 can be deprotonated to provide the anionic terminal carbide Tp' (CO){sub 2}W{triple_bond}C-Li; a resonance at 556 ppm in the {sup 13}C NMR spectrum has been assigned to the carbide carbon. Addition of excess Na[HBEt{sub 3}] to Tp'(CO){sub 2}W{triple_bond}C-H generates the anionic methylidene complex [Na] [Tp'(CO){sub 2}W{triple_bond}CH{sub 2}].
Date: September 1, 2002
Creator: Templeton, J.L.
Partner: UNT Libraries Government Documents Department

Theoretical studies of hydrocarbon combustion chemistry. Annual progress report

Description: The author reports here the results of DZP CISD calculations for methylcarbene. Geometry, symmetry, and vibrational modes for the radical are reported for both the singlet and the triplet state. Future work will focus on the ethyl radical-oxygen interaction relevant to hydrocarbon combustion.
Date: August 1, 1994
Creator: Schaefer, H. F. III
Partner: UNT Libraries Government Documents Department

Group 4 Metalloporphyrin diolato Complexes and Catalytic Application of Metalloporphyrins and Related Transition Metal Complexes

Description: In this work, the first examples of group 4 metalloporphyrin 1,2-diolato complexes were synthesized through a number of strategies. In general, treatment of imido metalloporphyrin complexes, (TTP)M=NR, (M = Ti, Zr, Hf), with vicinal diols led to the formation of a series of diolato complexes. Alternatively, the chelating pinacolate complexes could be prepared by metathesis of (TTP)MCl{sub 2} (M = Ti, Hf) with disodium pinacolate. These complexes were found to undergo C-C cleavage reactions to produce organic carbonyl compounds. For titanium porphyrins, treatment of a titanium(II) alkyne adduct, (TTP)Ti({eta}{sup 2}-PhC{triple_bond}CPh), with aromatic aldehydes or aryl ketones resulted in reductive coupling of the carbonyl groups to produce the corresponding diolato complexes. Aliphatic aldehydes or ketones were not reactive towards (TTP)Ti({eta}{sup 2}-PhC{triple_bond}CPh). However, these carbonyl compounds could be incorporated into a diolato complex on reaction with a reactive precursor, (TTP)Ti[O(Ph){sub 2}C(Ph){sub 2}O] to provide unsymmetrical diolato complexes via cross coupling reactions. In addition, an enediolato complex (TTP)Ti(OCPhCPhO) was obtained from the reaction of (TTP)Ti({eta}{sup 2}-PhC{triple_bond}CPh) with benzoin. Titanium porphyrin diolato complexes were found to be intermediates in the (TTP)Ti=O-catalyzed cleavage reactions of vicinal diols, in which atmospheric oxygen was the oxidant. Furthermore, (TTP)Ti=O was capable of catalyzing the oxidation of benzyl alcohol and {alpha}-hydroxy ketones to benzaldehyde and {alpha}-diketones, respectively. Other high valent metalloporphyrin complexes also can catalyze the oxidative diol cleavage and the benzyl alcohol oxidation reactions with dioxygen. A comparison of Ti(IV) and Sn(IV) porphyrin chemistry was undertaken. While chelated diolato complexes were invariably obtained for titanium porphyrins on treatment with 1,2-diols, the reaction of vicinal diols with tin porphyrins gave a number of products, including mono-, bis-alkoxo, and chelating diolato complexes, depending on the identity of diols and the stoichiometry employed. It was also found that tin porphyrin complexes promoted the oxidative cleavage of vicinal diols and the oxidation ...
Date: December 19, 2004
Creator: Du, Guodong
Partner: UNT Libraries Government Documents Department

Synthesis and study of novel silicon-based unsaturated polymers

Description: Novel unsaturated polymers have been synthesized and studied as precursors to silicon carbide and third order nonlinear optical materials. X ray structures were obtained. Kinetic and mechanistic studies of the unique thermal isomerization of dimethylenedisilacyclobutane to a carbene were conducted.
Date: June 19, 1995
Creator: Lin, J.
Partner: UNT Libraries Government Documents Department

Harnessing the Chemistry of CO2

Description: Our research program is broadly focused on activating CO{sub 2} through the use of organic and organometallic based catalysts. Some of our methods have centered on annulation reactions of unsaturated hydrocarbons (and carbonyl substrates) to provide a diverse array of carbocycles and heterocycles. We use a combination of catalyst discovery and optimization in conjunction with classical physical organic chemistry to elucidate the key mechanistic features of the cycloaddition reactions such that the next big advances in catalyst development can be made. Key to all of our cycloaddition reactions is the use of a sterically hindered, electron donating N heterocyclic carbene (NHC) ligand, namely IPr (or SIPr), in conjunction with a low valent nickel pre-catalyst. The efficacy of this ligand is two-fold: (1) the high {delta}-donating ability of the NHC increases the nucleophilicity of the metal center which thereby facilitates interaction with the electrophilic carbonyl and (2) the steric hindrance prevents an otherwise competitive side reaction involving only the alkyne substrate. Such a system has allowed for the facile cycloaddition to prepare highly functionalized pyrones, pyridones, pyrans, as well as novel carbocycles. Importantly, all reactions proceed under extremely mild conditions (room temperature, atmospheric pressures, and short reaction times), require only catalytic amounts of Ni/NHC and readily available starting materials, and afford annulated products in excellent yields. Our current focus revolves around understanding the fundamental processes that govern these cycloadditions such that the next big advance in the cyclization chemistry of CO{sub 2} can be made. Concurrent to our annulation chemistry is our investigation of the potential for imidazolylidenes to function as thermally-actuated CO{sub 2} sequestering and delivery agents.
Date: May 11, 2010
Creator: Louie, Janis
Partner: UNT Libraries Government Documents Department

Transition Metal Catalyzed Hydroarylation of Multiple Bonds: Exploration of Second Generation Ruthenium Catalysts and Extension to Copper Systems

Description: Catalysts provide foundational technology for the development of new materials and can enhance the efficiency of routes to known materials. New catalyst technologies offer the possibility of reducing energy and raw material consumption as well as enabling chemical processes with a lower environmental impact. The rising demand and expense of fossil resources has strained national and global economies and has increased the importance of accessing more efficient catalytic processes for the conversion of hydrocarbons to useful products. The goals of the research are to develop and understand single-site homogeneous catalysts for the conversion of readily available hydrocarbons into useful materials. A detailed understanding of these catalytic reactions could lead to the development of catalysts with improved activity, longevity and selectivity. Such transformations could reduce the environmental impact of hydrocarbon functionalization, conserve energy and valuable fossil resources and provide new technologies for the production of liquid fuels. This project is a collaborative effort that incorporates both experimental and computational studies to understand the details of transition metal catalyzed C-H activation and C-C bond forming reactions with olefins. Accomplishments of the current funding period include: (1) We have completed and published studies of C-H activation and catalytic olefin hydroarylation by TpRu{l_brace}P(pyr){sub 3}{r_brace}(NCMe)R (pyr = N-pyrrolyl) complexes. While these systems efficiently initiate stoichiometric benzene C-H activation, catalytic olefin hydroarylation is hindered by inhibition of olefin coordination, which is a result of the steric bulk of the P(pyr){sub 3} ligand. (2) We have extended our studies of catalytic olefin hydroarylation by TpRu(L)(NCMe)Ph systems to L = P(OCH{sub 2}){sub 3}CEt. Thus, we have now completed detailed mechanistic studies of four systems with L = CO, PMe{sub 3}, P(pyr){sub 3} and P(OCH{sub 2}){sub 3}CEt, which has provided a comprehensive understanding of the impact of steric and electronic parameters of 'L' on the catalytic hydroarylation of olefins. ...
Date: February 17, 2011
Creator: Gunnoe, T. Brent
Partner: UNT Libraries Government Documents Department

A Search for Thermal Isomerization of Olefins to Carbenes: Thermal Generations of the Silicon-Nitrogen Double Bond

Description: The first part of this thesis will search for the thermal isomerization of olefins to carbenes which is predicted to be a high energy process by calculations and has only been observed in a few strained olefins. The possibility of thermal isomerization of simple olefins to carbenes will be explored. Substitution of a silyl group on the double bond of an olefin allows a potential intermediate which has a {beta}-radical to the silyl group during the cis-trans isomerization. The effects of a trimethylsilyl group on this isomerization are the subject of this study. The second part of this thesis will include the generation and chemistry of intermediates containing a silicon-nitrogen double bond. The isomerization of parent silanimine to the aminosilylene was calculated to be a high energy process. New approaches to the silicon-nitrogen double bond will also be presented. 92 refs., 12 figs., 11 tabs.
Date: September 21, 1990
Creator: Zhang, Xianping
Partner: UNT Libraries Government Documents Department

Direct Functionalization of Nitrogen Heterocycles via Rh-Catalyzed C-H Bond Activation

Description: Nitrogen heterocycles are present in many compounds of enormous practical importance, ranging from pharmaceutical agents and biological probes to electroactive materials. Direct funtionalization of nitrogen heterocycles through C-H bond activation constitutes a powerful means of regioselectively introducing a variety of substituents with diverse functional groups onto the heterocycle scaffold. Working together, our two groups have developed a family of Rh-catalyzed heterocycle alkylation and arylation reactions that are notable for their high level of functional-group compatibility. This Account describes their work in this area, emphasizing the relevant mechanistic insights that enabled synthetic advances and distinguished the resulting transformations from other methods. They initially discovered an intramolecular Rh-catalyzed C-2-alkylation of azoles by alkenyl groups. That reaction provided access to a number of di-, tri-, and tetracyclic azole derivatives. They then developed conditions that exploited microwave heating to expedite these reactions. While investigating the mechanism of this transformation, they discovered that a novel substrate-derived Rh-N-heterocyclic carbene (NHC) complex was involved as an intermediate. They then synthesized analogous Rh-NHC complexes directly by treating precursors to the intermediate [RhCl(PCy{sub 3}){sub 2}] with N-methylbenzimidazole, 3-methyl-3,4-dihydroquinazolein, and 1-methyl-1,4-benzodiazepine-2-one. Extensive kinetic analysis and DFT calculations supported a mechanism for carbene formation in which the catalytically active RhCl(PCy{sub 3}){sub 2} fragment coordinates to the heterocycle before intramolecular activation of the C-H bond occurs. The resulting Rh-H intermediate ultimately tautomerizes to the observed carbene complex. With this mechanistic information and the discovery that acid co-catalysts accelerate the alkylation, they developed conditions that efficiently and intermolecularly alkylate a variety of heterocycles, including azoles, azolines, dihydroquinazolines, pyridines, and quinolines, with a wide range of functionalized olefins. They demonstrated the utility of this methodology in the synthesis of natural products, drug candidates, and other biologically active molecules. In addition, they developed conditions to directly arylate these heterocycles with aryl halides. The initial conditions ...
Date: February 4, 2008
Creator: Lewis, Jared; Bergman, Robert & Ellman, Jonathan
Partner: UNT Libraries Government Documents Department

Highly nucleophilic acetylide, vinyl, and vinylidene complexes. Progress report

Description: In the past year we have completed our studies of the halide-promoted carbonylation of imido ligands, extended our explorations of Cp(CO)(L)Mn-X complexes which possess highly reactive acetylide, vinylidene, carbyne, and vinylcarbyne ligands, and have briefly investigated the formation of bimetallic complexes using anionic carbene complexes. 5 figs.
Date: August 1, 1991
Partner: UNT Libraries Government Documents Department

Organometallic chemistry of bimetallic compounds. Final progress report

Description: This report consists of six sections: heterobimetallic dihydrides, early-late transition metal heterobimetallic compounds, amphiphilic carbene complexes and hydroxycarbene complexes, diiron compounds with bridging hydrocarbon ligands, diphosphine chelates with natural bite angles near 120 degrees, and synthesis and reactions of M=M compounds. (WET)
Date: July 1, 1991
Creator: Casey, C. P.
Partner: UNT Libraries Government Documents Department

Studies of coal structure using carbene chemistry

Description: The object of this grant was to react coal, derivatized forms of coal, and solvent swelled coal with carbenes (divalent carbon species) under mild conditions. These carbenes were to be prepared by treating the coal with several diazo compounds and then thermally decomposing them at relatively low temperatures (80--130{degree}C). The carbenes were to be chosen to show varying selectively toward aromatic rings containing heteroatom functionalities and toward polynuclear aromatic systems. In some instances, where selectivities toward aromatic and heteroaromatic ring systems were not known, model studies were to be carried out. Because of the generally mild conditions employed and the good selectivity anticipated, and actually observed with one particular system, it was expected that this methodology would provide structural information about the coal, along with data on the extent of occurrence and type of aromatic systems. After carbene reactions, treatment of the coal samples was to include extractions and thermolysis. Physical studies included thermogravimetric analysis, diffuse reflectance FT-IR spectroscopy, NMR ({sup 1}H and {sup 13}C) spectroscopy, gas chromatography, GC/MS and GC/FT-IR. 7 figs., 10 tabs.
Date: January 1, 1990
Partner: UNT Libraries Government Documents Department

Fundamental spectroscopic studies of carbenes and hydrocarbon radicals

Description: This document details activities during this reporting period topics discussed are: The first spectroscopic identification of the HCCCO and DCCCO radicals; detection of new vibrationally excited states of the carbon chain radicals CCH and CCD and the three-membered carbene ring, cyclopropenylidene; determination of an accurate structure of the cumulene carbene H{sub 2}CCC; analysis the hyperfine structure in the SiC radical; and the undertaking of a systematic search for new sulfur bearing radicals.
Date: May 1, 1992
Creator: Thaddeus, P. & Gottlieb, C.
Partner: UNT Libraries Government Documents Department

[Laser spectroscopy of hydrocarbon radicals]

Description: Several hydrocarbon reactive intermediates (carbenes, biradicals, etc.) were prepared in a supersonic jet expansion. heats of formation were determined for the isosmeric C{sub 3}H{sub 2} carbenes. Fits were made to the photoelectron spectra of c-C{sub 3}H{sub 2} and c- C{sub 4}H{sub 4}. Resonant MPI (multi-photon ionization?) spectra were obtained for allyl radical and its deuterated isotopomers.
Date: May 1, 1993
Partner: UNT Libraries Government Documents Department

Highly nucleophilic acetylide, vinyl, and vinylidene complexes. Progress report

Description: The research was divided into the following: studies of nucleophilic and chiral acetylide complex [Cp(CO)(PPh{sub 3})Mn-C{triple_bond}CR]{sup {minus}}; nucleophilic addition of carbene anions to organic ligands on electrophilic complexes; halide-promoted carbonylation of imido ligands; binuclear Fe{sub 2} complexes with bridging organonitrogen ligands; addition and cycloaddition reactions of carbyne complex [Cp(CO){sub 2}Re{triple_bond}CTol]{sup +}; addition and cycloaddition reactions of methylcarbyne complexes [Cp(CO){sub 2}M{triple_bond}CCH{sub 3}]{sup +} and vinylidene complexes Cp(CO){sub 2}M{double_bond}C{double_bond}CH{sub 2} (M=Mn, Re); studies of generation and reactivity of vinylcarbene complexes formed from reaction of manganese carbene anions and aldehydes; and addition of oxo ligands of nucleophilic oxo complexes to organic ligands on electrophilic metal centers.
Date: June 15, 1992
Partner: UNT Libraries Government Documents Department

Unimolecular and bimolecular reactions induced by state-specific vibrational excitation. Progress report

Description: Toward the goal of understanding the role of vibrational energy in chemical reactions related to energy production, we have made several advances. They include the understanding of chemical properties of highly vibrationally excited molecules, the characterization of vibrationally excited radicals, and the development of experimental techniques to extend our ability to investigate transient and reactive chemical species. 11 refs., 1 fig.
Date: November 1, 1991
Creator: Dai, Hai-Lung
Partner: UNT Libraries Government Documents Department

Highly nucleophilic acetylide, vinyl, and vinylidene complexes

Description: The research was divided into the following: studies of nucleophilic and chiral acetylide complex [Cp(CO)(PPh[sub 3])Mn-C[triple bond]CR][sup [minus]]; nucleophilic addition of carbene anions to organic ligands on electrophilic complexes; halide-promoted carbonylation of imido ligands; binuclear Fe[sub 2] complexes with bridging organonitrogen ligands; addition and cycloaddition reactions of carbyne complex [Cp(CO)[sub 2]Re[triple bond]CTol][sup +]; addition and cycloaddition reactions of methylcarbyne complexes [Cp(CO)[sub 2]M[triple bond]CCH[sub 3]][sup +] and vinylidene complexes Cp(CO)[sub 2]M[double bond]C[double bond]CH[sub 2] (M=Mn, Re); studies of generation and reactivity of vinylcarbene complexes formed from reaction of manganese carbene anions and aldehydes; and addition of oxo ligands of nucleophilic oxo complexes to organic ligands on electrophilic metal centers.
Date: June 15, 1992
Partner: UNT Libraries Government Documents Department