Browsing by Author "T. Brent Gunnoe, Committee Chair"

Filter results by typing the first few letters
Now showing 1 - 9 of 9
  • No Thumbnail Available
    Activation of Carbon-Hydrogen Bonds Mediated by Ru(II) Complexes
    (2007-05-01) Pittard, Karl A.; David A. Shultz, Committee Member; James D. Martin, Committee Member; Edmond F. Bowden, Committee Member; T. Brent Gunnoe, Committee Chair
    The RuII complex TpRu(CO)(NCMe)Me (Tp = hydridotris(pyrazolyl)borate) initiates carbon-hydrogen bond activation at the 2-position of furan and thiophene to produce methane and TpRu(CO)(NCMe)Ar (Ar = 2-furyl or 2-thienyl). Solid-state structures have been determined for TpRu(CO)(NCMe)(2-thienyl) and [TpRu(CO)(-C,S-thienyl)]2. The complex TpRu(CO)(NCMe)(2-furyl) serves as a catalyst for the formation of 2-ethylfuran from ethylene and furan. Similar catalytic reactivity was observed with TpRu(CO)(NCMe)(2-thienyl) for the production of 2-ethylthiophene. Density functional theory (DFT) calculations of the C-H activation of furan by {(TAB)Ru(CO)Me} (TAB = tris(azo)borate) indicate that the C-H activation sequence does not proceed through a RuIV oxidative addition intermediate. The reaction of TpRu(CO)(NCMe)Me and pyrrole forms TpRu(CO){ 2-N,N-(H)N=C(Me)(NC4H3)}. The formation of complex TpRu(CO){2-N,N-(H)N=C(Me)(NC4H3)} involves the cleavage of the N-H bond and 2-position C-H bond of pyrrole as well as a C-C bond forming step between pyrrole and the acetonitrile ligand of {TpRu(CO)(NCMe)}. Mechanistic studies indicate that the most likely reaction pathway involves initial metal-mediated N-H activation of pyrrole to produce TpRu(CO)(NCMe)(N-pyrrolyl) followed by C-C bond formation and proton transfer. Complex TpRu(CO)(NCMe)(N-pyrrolyl) has been independently prepared. At elevated temperatures, TpRu(CO)(NCMe)(N-pyrrolyl) converts to TpRu(CO){2-N,N-(H)N=C(Me)(NC4H3)}. Single crystal X-ray analysis has been achieved for TpRu(CO)(NCMe)(N-pyrrolyl), [TpRu(CO)(NCMe)(1-O-OC4H8) and TpRu(CO){2-N,N-(H)N=C(Me)(NC4H3)}. Computational studies support the suggested selectivity for initial N-H bond cleavage in preference to C-H bond activation. Rational design for a more electron-poor hydroarylation catalyst was discussed. Synthesis of Mp (Mp = tris(pyrazolyl)methane) complexes of the type [MpRu(PPh3)(CO)H]BAr'4, [MpRu(PPh3)(CO)Cl]BAr'4, [MpRu(PPh3)(PMe3)Cl]Cl, [MpRu(PPh3)(PMe3)Cl]BAr'4, [MpRu(PPh3)2Cl]BAr'4, [MpRu(PPh3){P(OMe)3}Cl]Cl, [MpRu(PPh3)(NCMe)Cl]BAr'4, [MpRu(PPh3)(NCMe)Cl]BAr'4 and [MpRu(PPh3)(CO)Cl]BAr'4 accomplished. A single-crystal X-ray diffraction study was carried out on the complex [MpRu(PPh3)(PMe3)Cl]Cl. [MpRu(PPh3)2Me]BAr'4 was prepared and examined by Cyclic Voltammetry (CV) where the E1/2 = 1.19 V. C-H activation was observed when [MpRu(PPh3)2Me]BAr'4 was heated in neat C6D6. Orthometalation appears to dominate reactivity via intramolecular C-H activation of a PPh3 ligand, however CH3D was produced at elevated temperatures. A series of Ep (Ep = tris(pyrazolyl)ethane) complexes of the type MpRu(Cl)2PR3 (R = Ph, OMe, or Me) were also synthesized. The [EpRu(PPh3)(NCMe)(Cl)]Cl and [EpRu(PPh3)(PMe3)(Cl)]Cl complexes were observed spectroscopically as intermediates in these syntheses. Improved synthesis of [MpRu(PPh3)2Cl]Cl was also accomplished by improving the yield by 23%, over the previously reported yield of 53%.
  • No Thumbnail Available
    Preparation and characterization of a ruthenium(II) catalyst for radical polymerization of olefins.
    (2003-04-17) Arrowood, Benjamin Nathan; T. Brent Gunnoe, Committee Chair; James D. Martin, Committee Member; Christopher B. Gorman, Committee Member
    A ruthenium(II) complex TpRu(CO)(CH3)(NCCH3) (Tp = hydridotris(pyrazolyl)borate) was prepared from TpRu(CO)2(CH3) by refluxing in acetonitrile with (CH3)3NO. Heating a solution of TpRu(CO)(CH3)(NCCH3) in CDCl3 to 50 oC with various equivalents of CD3CN indicates that the Ru-NCCH3 undergoes exchange with CD3CN and is independent of CD3CN concentration. Reactions with styrene or methyl methacrylate in the presence of catalytic quantities of TpRu(CO)(CH3)(NCCH3) at 90 °C result in the production of polystyrene and polymethyl methacrylate, respectively. An inverse dependence of polystyrene molecular weight on concentration of added cumene indicates that a radical polymerization mechanism is likely. In addition, the polymerization of styrene or methyl methacrylate occurs in the presence of carbon tetrachloride or methyl dichloroacetate with catalytic quantities of TpRu(CO)(CH3)(NCCH3) at 90°. In both cases, polymer conversion rates are sluggish and molecular weight distributions are broad. The slow reaction rates are attributed to a high Ru(III/II) redox couple that favors Ru(II). Reactions with TpRu(CO)(CH3)(NCCH3) in benzene charged with ethylene at 90 °C do not produce polyethylene. Rather, catalytic synthesis of ethylbenzene as well as 1,3- and 1,4-diethylbenzene is observed.
  • No Thumbnail Available
    Synthesis and Characterization of Ruthenium(II) and Platinum(IV) Complexes with Anionic Heteroatomic Ligands
    (2009-08-13) Gurkin, Joshua Taylor; T. Brent Gunnoe, Committee Chair; Reza A. Ghiladi, Committee Member; Elon A. Ison, Committee Member; Maria T. Oliver-Hoyo, Committee Member
    Isolated and fully characterized complexes of late transition metals in low oxidation states possessing amido and alkoxo ligands are relatively rare. These ligands often exhibit nucleophilic and/or basic reactivity. This reactivity is due, at least in part, to the disruption of ligand to metal à €-bonding. Reports of early transition metals with low d-electron counts with imido ligands facilitating C-H activation suggest that if later transition metals with amido or aryloxo ligands can be isolated, C-H activation reactivity may be observed. Ruthenium(II) complexes that catalyze the H/D exchange of N-H and O-H protons at anilido and hydroxo ligands, respectively, with deuterated solvents have been reported, and studies of related systems could shed significant light on C-H activation in these types of reactions. Observing changes in the rate of C-H activation based on specific changes to transition metal complexes could give insight into the creation of highly active C-H activation catalysts. Presented here are synthetic efforts toward late transition metal complexes with formally anionic heteroatomic ligands. The synthesis and initial characterization of [EpRu(Cl)(PPh3)(NCMe)][Cl], [EpRu(py)2Cl][Cl], [EpRu(py)2Cl][Cl], [EpRu(OHMe)(PMe3)(Cl)][BAr’4] are reported {Ep = 1,1,1-tris(pyrazolyl)ethane, py = N-pyridine, Ar’ = 3,5-(CF3)-C6H3}. The lack of solubility yielded these complexes ineffective for further synthetic manipulation. Additionally presented is the synthesis and characterization of (tbpy)Pt(Me)2(I)2 and (tbpy)Pt(Me)(NHPh)(I)2 (tbpy = 4,4’-tert-butyl-2,2’-bipyridine). Attempted syntheses of (tbpy)Pt(NHPh)2(I)2 and (tbpy)Pt(Cl)(NHPh)(I)2 are also reported. Initial reactivity of (tbpy)Pt(Me)2(I)2 and the decomposition of (tbpy)Pt(Me)(NHPh)(I)2 are further reported.
  • No Thumbnail Available
    Synthesis and Reactivity of Copper Complexes Possessing Non-dative Ligands
    (2007-07-05) Blue, Elizabeth Dodge; T. Brent Gunnoe, Committee Chair
    C-N bonds are prevalent in many areas of chemistry including natural products, pharmaceuticals, conducting polymers, and materials for electronic applications. Late transition metals are often used to catalyze carbon-nitrogen bond-forming reactions with diverse substrates and under relatively mild conditions. Hydroamination and aryl amination catalysis may proceed via Cu(I) amido complexes, and Cu-catalyzed aziridination catalysis may proceed via Cu(III) nitrene intermediates. Detailed investigation of these potential intermediates and reaction mechanisms could further the development of these critical reactions. Besides potential catalytic application, many late transition-metal non-dative complexes possess significant basic and nucleophilic reactivity. Presented herein are the isolation and characterization of a number of new copper(I) halide complexes and the first two monomeric examples of copper(I) amido complexes, (dtbpe)Cu(NHPh) and (IPr)Cu(NHPh). These Cu(I) anilido complexes have been shown to be more nucleophilic than a related Ru(II) anilido complex in reactivity studies with bromoethane, and reveal increasing nucleophilicity in the order (SIPr)Cu(NHPh) < (IPr)Cu(NHPh) < (IMes)Cu(NHPh) < (dtbpe)Cu(NHPh). (IPr)Cu(NHPh) is thermodynamically favored over (IPr)Cu(Ph)⁄NH₂Ph or [(IPr)Cu(μ-H)]₂⁄NH₂Ph, respectively. Computational studies are consistent with the observed reactivity and indicate strong Cu-N bonds with nucleophilic amido nitrogen. (dtbpe)Cu(NHPh) and (IPr)Cu(NHPh) are active for hydroamination catalysis of electron-withdrawing olefins, and (IPr)Cu(NHPh) is observed to undergo stoichiometric and catalytic aryl amination with PhI and PhOTf. The mechanism and analysis of the scope of these reactions will continue to be investigated. Reactions towards synthesis of a Cu(III) nitrene complex with LCu(I) (L = dtbpe, NN, or IPr) complexes have largely resulted in decomposition to amine products and Cu(II) species. However, reactions with (NN)Cu(NCMe) complexes and phenyl azide did result in formation of a non-isolable transient species which may be either a Cu(III) nitrene or a Cu(II) species. Reaction of (IPr)Cu(OTf) with strong acid yields a protonated carbene ligand indicated by an downfield peak which binds η² through the imidazolium phenyl ring of the amido complex. The synthesis and reactivity studies described herein have provided a foundation for continued fundamental studies of copper(I) non-dative species and mechanistic and applied C-X (X = N, O, or S) bond-forming catalytic investigations.
  • No Thumbnail Available
    Synthesis and Reactivity of Ruthenium Amine and Amido Complexes.
    (2005-03-01) Conner, David M; David Shultz, Committee Member; Edmond F. Bowden, Committee Member; T. Brent Gunnoe, Committee Chair; James Martin, Committee Member
    Late transition metal complexes with non-dative and π-donating ligands are important substrates in a variety of synthetic transformations including C-N or C-O bond forming processes and C-H bond activation reactions. Examples of such complexes are few relative to early and middle transition elements in high oxidation states, and the understanding of the chemistry of such systems with amido, oxide, imido, or oxo ligands has lagged compared to related M-C or M-H linkages. A series of Ru(II) amido complexes of the type TpRu(L)(L')NHR (L = L' = PMe3 or P(OMe)3 or L = CO and L' = PPh3; R = H, Ph, or tBu) were prepared and characterized. These complexes exhibit basic reactivity and will deprotonate C-H bonds as evidenced by the reactivity with weak acids such as 1,4-cyclohexadiene or phenylacetylene. The nucleophilicity of the complexes was also examined by reaction with ethylbromide. In addition, oxidation of the phenyl amido complexes with AgOTf, Cp2FePF6, or I2 resulted in 4,4' carbon-carbon coupling of the aryl group of the anilido ligands to produce the bimetallic complexes [TpRu(L)(L')NHC6H4-]2[X]2 (X = OTf -, PF6-, or I-). The five-coordinate amido complexes (PCP)Ru(CO)NHR (PCP = C6H3(CH2PtBu2)2; R = H or Ph) were synthesized and characterized. The parent amido complex was prepared by deprotonation of (PCP)Ru(CO)(NH3)Cl and the phenyl amido
  • No Thumbnail Available
    Synthesis and Reactivity of Ruthenium and Platinum Complexes with Non-dative Heteroatomic Ligands: Studies of Carbon-hydrogen Bond Activation
    (2007-12-18) Feng, Yuee; James D. Martin, Committee Member; David A. Shultz, Committee Member; Paul Maggard, Committee Member; T. Brent Gunnoe, Committee Chair
    Several ruthenium complexes with non-dative heteroatomic ligands were prepared and fully characterized, including TpRu(PMe3)2X (X = OH, OPh, OMe, SH; Tp = hydridotris(pyrazolyl)borate). At elevated temperatures (90 °C — 130 °C), complexes of the type TpRu(PMe3)2X (X = OH, OPh, Me, Ph or NHPh) undergo regioselective H⁄D exchange with deuterated arenes. In addition, for X = OH or NHPh, H⁄D exchange occurs at hydroxo and anilido ligands, respectively. For X = OH, OPh, Me, Ph or NHPh, isotopic exchange occurs at the Tp 4-positions with only minimal deuterium incorporation at the Tp 3- or 5-positions. TpRu(PMe3)2Cl, TpRu(PMe3)2OTf (OTf = trifluoromethanesulfonate) and TpRu(PMe3)2SH do not initiate H⁄D exchange in C6D6 after extended periods of time at elevated temperatures. Mechanistic studies indicate that the likely pathway for the H⁄D exchange involves ligand dissociation (PMe3 or NCMe), Ru-mediated activation of an aromatic C-D bond, and deuteration of basic heteroatomic ligand (hydroxo or anilido) or Tp positions via intermolecular D+ transfer. The Ru(II) complexes TpRu(PMe3)2OR (R = H or Ph) react with excess phenylacetylene at elevated temperatures to produce the phenylacetylide complex TpRu(PMe3)2(CCPh). Kinetic studies indicate that the reaction of TpRu(PMe3)2OH and phenylacetylene likely proceeds through a pathway that involves TpRu(PMe3)2OTf as a catalyst. The reaction of TpRu(PMe3)2OH with 1,4-cyclohexadiene at elevated temperature forms benzene and TpRu(PMe3)2H, while TpRu(PMe3)2OPh does not react with 1,4-cyclohexadiene even after 20 days at 85 C. The paramagnetic Ru(III) complex [TpRu(PMe3)2OH][OTf] is formed upon single-electron oxidation of TpRu(PMe3)2OH with AgOTf. Reactivity studies suggest that [TpRu(PMe3)2OH][OTf] initiates reactions, including hydrogen atom abstraction, with C-H bonds that have bond dissociation energy ≤ 82 kcal⁄mol. Experimentally, the O-H bond strength of the Ru(II) cation [TpRu(PMe3)2(OH2)[OTf] is estimated to be between 82 and 85 kcal⁄mol, while computational studies yield a BDE of 84 kcal⁄mol, which are in reasonable agreement with the observed reactivity of [TpRu(PMe3)2OH]+. The preparation of the monomeric octahedral platinum(IV) complex (NCN')PtMe2NHPh (NCN' = 2,6-bis[(3,5-dimethylpyrazol-1-yl)methyl]bromobenzene) was achieved through metathesis of platinum triflate complex with alkali metal amido complex. This complex has been isolated and characterized by 1H NMR spectroscopy.
  • No Thumbnail Available
    Synthesis and Reactivity or Ruthenium(II) and Platinum(IV) complexes
    (2008-01-03) Sumiyoshi, Taisuke; T. Brent Gunnoe, Committee Chair
  • No Thumbnail Available
    Synthesis andRreactivity of Copper(I), Copper(II), Platinum(II) and Platinum(IV) Complexes with Non-dative Heteroatomic Ligands
    (2008-08-20) Munro-Leighton, Colleen; Christian Melander, Committee Member; Elon Ison, Committee Member; James D. Martin, Committee Member; T. Brent Gunnoe, Committee Chair
    Examples of late transition metal complexes with amido, alkoxo and sulfido ligands are relatively rare in part due to enhanced reactivity based on nucleophilicity and basicity of the heteroatomic ligand (X). The highly nucleophilic and basic character of formally anionic X ligands coordinated to metal centers with low oxidation states is attributable to the disruption of ligand-to-metal pi-bonding. Examples of common reactivity for these systems include nucleophilic addition reactions, insertions of unsaturated substrates, acid/base chemistry with acidic C-H bonds and C-H activation reactions with aromatic substrates. In addition to fundamental reactivity studies, these complexes also offer opportunities for incorporation into catalytic processes. Late transition metal complexes with non-dative X ligands have been implicated in several C-X bond forming reactions and have been demonstrated to activate non-polar substrates. Thus, in order to advance the understanding of these reactive systems and to exploit the prospects for synthetic applications toward small molecule transformations, further study is warranted. Presented herein is the study of (IPr)Cu(NR2), (IPr)Cu(OR) and (IPr)Cu(SR) {IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene} complexes in the catalytic hydroamination of electron-deficient olefins toward regioselective formation of C-N, C-O and C-S bonds. The substrate scope encompasses alkyl and aryl amines, including primary and secondary variants, as well as alcohols and thiols. Olefins with cyano, acyl, and ester functionalities and vinylarenes are reactive. In a demonstration of potential application, the hydroamination of p-nitrostyrene with N-methylbenzylamine by (IPr)Cu(NHPh) provides a straight-forward single-step route to an anti-arrhythmic agent. Mechanistic studies are consistent with a reaction pathway that involves intermolecular nucleophilic addition of the Cu-amido to free olefin. In an effort to obtain more active catalyst systems that are reactive with unactivated substrates, the preparation of Cu(II), Pt(IV) and Pt(II) amido species has been targeted. The Pt(IV) amido complex (NCN)PtMe2(NHPh) {NCN = 2,6-(pyrazolyl-CH2)2C6H3} has been synthesized and isolated, and reactivity studies have shown the amido moiety to have basic and nucleophilic character. Although (NCN)PtMe2(NHPh) reacts with dihydrogen, C-H activation of benzene does not occur, which is likely due to coordinative saturation of the Pt(IV) complex. To potentially address this issue, two square planar Pt(II) amido species have been synthesized. Initial reactivity studies with (tbbpy)Pt(Me)(NHPh) and (tbbpy)PtCl(NHPh) (tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine) indicate that these complexes initiate C-H activation with benzene. These developments could prove beneficial for future efforts toward activation and functionalization of small molecules.
  • No Thumbnail Available
    Synthesis, Characterization and Reactivity of Ru(II) and Rh(I) Hydrocarbyl and Hydride Complexes
    (2008-06-27) Lee, John; Paul A. Maggard, Committee Member; Elon Ison, Committee Member; T. Brent Gunnoe, Committee Chair; Christian Melander, Committee Member