Publications

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We disclose unprecedented synergistic bimetallic Ni/Ag and Ni/Cu catalysts for regioselective γ,δ-diarylation of unactivated alkenes in simple ketimines with aryl halides and arylzinc reagents. The bimetallic synergy, which generates cationic Ni(II) species during reaction, promotes migratory insertion and transmetalation steps and suppresses β-H elimination and cross-coupling, the major side reactions that cause serious problems during alkene difunctionalization. This diarylation reaction proceeds at remote locations to imines to afford, after simple H+ workup, diversely substituted γ,δ-diaryl ketones that are otherwise difficult to access readily with existing methods.

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The impact on the morphology nanoceramic materials generated from group 4 metal alkoxides ([M(OR)4]) and the same precursors modified by 6,6′-(((2-hydroxyethyl)azanediyl)bis(methylene))bis(2,4-di-tert-butylphenol) (referred to as H3-AM-DBP2 (1)) was explored. The products isolated from the 1:1 stoichiometric reaction of a series of [M(OR)4] where M = Ti, Zr, or Hf; OR = OCH(CH3)2(OPri); OC(CH3)3(OBut); OCH2C(CH3)3(ONep) with H3-AM-DBP2 proved, by single crystal X-ray diffraction, to be [(ONep)Ti(k4(O,O′,O′′,N)-AM-DBP2)] (2), [(OR)M(μ(O)-k3(O′,O′′,N)-AM-DBP2)]2 [M = Zr: OR = OPri, 3·tol; OBut, 4·tol; ONep, 5·tol; M = Hf: OR = OBut, 6·tol; ONep, 7·tol]. The product from each system led to a tetradentate AM-DBP2 ligand and retention of a parent alkoxide ligand. For the monomeric Ti derivative (2), the metal was solved in a trigonal bipyramidal geometry, whereas for the Zr (3-5) and Hf (6, 7) derivatives a symmetric dinuclear complex was formed where the ethoxide moiety of the AM-DBP2 ligand bridges to the other metal center, generating an octahedral geometry. High quality density functional theory level gas-phase electronic structure calculations on compounds 2-7 using Gaussian 09 were used for meaningful time dependent density functional theory calculations in the interpretation of the UV-vis absorbance spectral data on 2-7. Nanoparticles generated from the solvothermal treatment of the ONep/AM-DBP2 modified compounds (2, 5, 7) in comparison to their parent [M(ONep)4] were larger and had improved regularity and dispersion of the final ceramic nanomaterials.

This project focused on providing a fundamental mechanistic understanding of the complex degradation mechanisms associated with Pellet/Clad Debonding (PCD) through the use of a unique suite of novel synthesis of surrogate spent nuclear fuel, in-situ nanoscale experiments on surrogate interfaces, multi-modeling, and characterization of decommissioned commercial spent fuel. The understanding of a broad class of metal/ceramic interfaces degradation studied within this project provided the technical basis related to the safety of high burn-up fuel, a problem of interest to the DOE.

In an effort to generate single-source precursors for the production of metal-siloxide (MSiOx) materials, the tris(trimethylsilyl)silanol (H-SST or H-OSi(SiMe3)3 (1) ligand was reacted with a series of group 4 and 5 metal alkoxides. The group 4 products were crystallographically characterized as [Ti(SST)2(OR)2] (OR = OPri (2), OBut (3), ONep (4)); [Ti(SST)3(OBun)] (5); [Zr(SST)2(OBut)2(py)] (6); [Zr(SST)3(OR)] (OR = OBut (7), ONep, (8)); [Hf(SST)2(OBut)2] (9); and [Hf(SST)2(ONep)2(py)n] (n = 1 (10), n = 2 (10a)) where OPri = OCH(CH3)2, OBut = OC(CH3)3, OBun = O(CH2)3CH3, ONep = OCH2C(CH3)3, py = pyridine. The crystal structures revealed varied SST substitutions for: monomeric Ti species that adopted a tetrahedral (T-4) geometry; monomeric Zr compounds with coordination that varied from T-4 to trigonal bipyramidal (TBPY-5); and monomeric Hf complexes isolated in a TBPY-5 geometry. For the group 5 species, the following derivatives were structurally identified as [V(SST)3(py)2] (11), [Nb(SST)3(OEt)2] (12), [Nb(O)(SST)3(py)] (13), 2[H][(Nb(μ-O)2(SST))6(μ6-O)] (14), [Nb8O10(OEt)18(SST)2·1/5Na2O] (15), [Ta(SST)(μ-OEt)(OEt)3]2 (16), and [Ta(SST)3(OEt)2] (17) where OEt = OCH2CH3. The group 5 monomeric complexes were solved in a TBPY-5 arrangement, whereas the Ta of the dinculear 16 was solved in an octahedral coordination environment. Thermal analyses of these precursors revealed a stepwise loss of ligand, which indicated their potential utility for generating the MSiOx materials. The complexes were thermally processed (350-1100 °C, 4 h, ambient atmosphere), but instead of the desired MSiOx, transmission electron microscopy analyses revealed that fractions of the group 4 and group 5 precursors had formed unusual metal oxide silica architectures.

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Molecular tracers that can be selectively placed underground and uniquely identified at the surface using simple on-site spectroscopic methods would significantly enhance subsurface fluid monitoring capabilities. To ensure their widespread utility, the solubility of these tracers must be easily tuned to oil- or water-wet conditions as well as reducing or eliminating their propensity to adsorb onto subsurface rock and/or mineral phases. In this work, molecular dynamics simulations were used to investigate the relative solubilities and mineral surface adsorption properties of three candidate tracer compounds comprising Mg–salen derivatives of varying degrees of hydrophilic character. Simulations in water–toluene liquid mixtures indicate that the partitioning of each Mg–salen compound relative to the interface is strongly influenced by the degree of hydrophobicity of the compound. Simulations of these complexes in fluid-filled mineral nanopores containing neutral (kaolinite) and negatively charged (montmorillonite) mineral surfaces reveal that adsorption tendencies depend upon a variety of parameters, including tracer chemical properties, mineral surface type, and solvent type (water or toluene). Simulation snapshots and averaged density profiles reveal insight into the solvation and adsorption mechanisms that control the partitioning of these complexes in mixed liquid phases and nanopore environments. As a result, this work demonstrates the utility of molecular simulation in the design and screening of molecular tracers for use in subsurface applications.

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A pair of thallium salen derivatives was synthesized and characterized for potential use as monitors (or taggants) or as models for Group 13 complexes for subterranean fluid flows. These precursors were isolated from the reaction of thallium ethoxide with N,N′-bis(3,5-di-tert-butylsalicylidene)-ethylenediamine (H2-salo-But), or N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-phenylenediamine (H2-saloPh-But). The products were identified by single crystal X-ray diffraction as: [((μ-O)2,κ1-(N)(N′)salo-But)Tl2] (1) and {[((μ-O)2saloPh-But)Tl2][((μ-O)2,κ1-(N)(N′)saloPh-But)Tl2]} (2). Both structures are similar, wherein each O atom of the salo moiety bridges the two Tl atoms, leading to a Tl⋯Tl interaction, which is further stabilized by an intramolecular π-bond with neighboring phenyl rings. For 1, an additional Tl⋯N interaction was solved for each metal center; whereas, for 2, one of the two molecules in the matrix has a weak Tl⋯N interaction but no bonding noted in the other molecule. Both Density Functional Theory (DFT) calculations and variable temperature solution 205Tl NMR studies of 1 and 2 further confirmed the Tl⋯Tl interaction. The UV-vis absorbance spectra of these compounds had an absorbance peak at 392 nm for 1 and a broad absorbance peak centered at 469 nm for 2, which were found to be in good agreement with the DFT calculated spectra that were dominated by the singlet state. Fluorescence emission and excitation studies reveal absorptions at 360 and 380 nm for 1 and 2, respectively, which are attributed to the Tl⋯Tl metal centers. To demonstrate practicality, fluorescence spectra of 1 and 2 were obtained using a handheld 405 nm cw laser pointer and portable spectrometer where compound 1 was found to glow 15 times brighter than compound 2. Only compound 1 was found to survive the simulated deep-well conditions explored, which was attributed to the Tl⋯N interaction noted for 1 but not for 2.

The first (N=N)2- complex of a rare-earth metal with an end-on dinitrogen bridge, {K(crypt)}2{[(R2N)3Sc]2[μ-η1:η1-N2]} (crypt = 2.2.2-cryptand, R = SiMe3), has been isolated from the reduction of Sc(NR2)3 under dinitrogen at -35 °C and characterized by X-ray crystallography. The structure differs from the characteristic side-on structures previously observed for over 40 crystallographically characterized rare-earth metal (N=N)2- complexes of formula [A2Ln(THF)x]2[μ- η2:η2-N2] (Ln = Sc, Y, and lanthanides; x = 0, 1; A = anionic ligand such as amide, cyclopentadienide, and aryloxide). The 1.221(3) Å N - N distance and the 1644 cm-1 Raman stretch are consistent with the presence of an (N=N)2- bridge. The observed paramagnetism of the complex by Evans method measurements is consistent with DFT calculations that suggest a triplet (3A2) ground state in D3 symmetry involving two degenerate Sc - N2 - Sc bonding orbitals. Upon brief exposure of the orange Sc3+ bridging dinitrogen complex to UV-light, photolysis to form the monomeric Sc2+ complex, [K(crypt)][Sc(NR2)3], was observed. Conversion of the Sc2+ complex to the Sc3+ dinitrogen complex was not observed with this crypt system, but it did occur with the 18-crown-6 (crown) analog which formed {K(crown)}2{[(R2N)3Sc]2[μ- η1:η1-N2]}. This suggests the importance of the alkali metal chelating agent in the reversibility of dinitrogen binding in this scandium system.

The Chemistry Science Investigation: Dognapping Workshop was designed to (i) target and inspire fourth grade students to view themselves as Junior Scientists before their career decisions are solidified; (ii) enable hands-on experience in fundamental scientific concepts; (iii) increase public interaction with science, technology, engineering, and mathematical personnel by providing face-to-face opportunities; (iv) give teachers a pathway forward for scientific resources; (v) meet the New Mexico K-5 Science Benchmark Performance Standards; (vi) most importantly, ensure everyone has fun! For this workshop, the students are told they will be going to see a Chemistry Magic Show, but the performance is stopped when the Chemistry Dog is reportedly stolen. The students first clear their names using a series of interactive stations and then apply a number of science experiments to solve the mystery. This report describes the workshop in detail, which is suitable for large (100 students per day) audiences but has flexibility to be modified for much smaller groups. An identical survey was given three times (before, immediately after, and 2 months after the workshop) to determine the impact on the students' perception of science and scientists as well as determine the effectiveness in relaying scientific concepts through retention time. Survey responses indicate that scientific information pertaining to the workshop is retained for up to 2 months.

Our team has investigated a series of soluble coordination complexes for use as tags to monitor underground fluid flows in reservoirs. While most of the metal-ligand (M-L) complexes were based on the dianionic salen family of ligands, conceptually other ligands such as porphyrins or phthalocyanines could be used with similar success. Detection and identification of these species in solution were performed by inductively coupled plasma (ICP) or Raman/resonance Raman (rR) spectroscopy. The preparation of a large number of new M-L salen complexes was accomplished. Complexes were prepared that were soluble in either water or hydrocarbons to allow for flexibility in use. Unambiguous identification of these complexes allowed for meaningful molecular dynamics (MD) calculations to be performed, so that the attraction of the M-L complexes to either the rock formation or the liquid media could be evaluated. The use of soluble M-L species was found to avoid issues of rock deposition.

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