17 research outputs found

    Rh(III)-Catalyzed Cascade Oxidative Olefination/Cyclization of Picolinamides and Alkenes via C–H Activation

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    Rh­(III)-catalyzed cascade oxidative alkenylation/cyclization of picolinamides and alkenes to furnish pyrido pyrrolone derivatives is described, in which three C–H bonds and one N–H bond broke, while one C–C bond and one C–N bond formed. The reaction proceeded with high yield and high regioselectivity and stereoselectivity. Moreover, copper acetate can also be used in catalytic amounts with O<sub>2</sub> serving as the terminal oxidant

    Probing the Structural, Bonding, and Magnetic Properties of Cobalt Coordination Complexes: Co–Benzene, Co–Pyridine, and Co–Pyrimidine

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    Neutral and anionic Co<sub>1,2</sub>(benzene)<sub>1,2</sub>, Co<sub>1,2</sub>(pyridine)<sub>1,2</sub>, and Co<sub>1,2</sub>(pyrimidine)<sub>1,2</sub> complexes have been investigated within the framework of an all-electron gradient-corrected density functional theory. The ground-state structures for each size clusters were identified based on the geometry optimization. Meanwhile, their electron affinities and vertical detachment energies were predicted and compared with the experimental values. By analyzing the pattern of highest occupied molecular orbitals (HOMOs), we found that the bond formation of these Co–organic complexes mainly arises from the 3d/4s electrons of the cobalt atoms and the π-cloud of the organic molecules. More importantly, we presented an approach to map and analyze the Co–organic interactions from another perspective. The scatter plots of the reduced density gradient (RDG) versus ρ allow us to identify the different types of interactions, and the maps of the gradient isosurfaces show a rich visualization of chemical bond and steric effects. Their magnetic properties were studied by determining the spin magnetic moments and visualizing the spin density distributions. Finally, the natural population analysis (NPA) charge was calculated to achieve a deep insight into the distribution of electron density and the reliable charge-transfer information

    Copper-Catalyzed Carboxylation of Alkenylzirconocenes with Carbon Dioxide Leading to ι,β-Unsaturated Carboxylic Acids

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    A variety of alkenylzirconocenes were efficiently carboxylated by CO<sub>2</sub> utilizing the (IMes)­CuCl catalyst yielding the corresponding ι,β-unsaturated carboxylic acids in good yields. This reaction could be carried out in a one-pot operation via sequential carbozirconation of alkynes and carboxylation using CO<sub>2</sub> as starting materials under room temperature

    Rh(III)-Catalyzed Cascade Oxidative Olefination/Cyclization of Picolinamides and Alkenes via C–H Activation

    No full text
    Rh­(III)-catalyzed cascade oxidative alkenylation/cyclization of picolinamides and alkenes to furnish pyrido pyrrolone derivatives is described, in which three C–H bonds and one N–H bond broke, while one C–C bond and one C–N bond formed. The reaction proceeded with high yield and high regioselectivity and stereoselectivity. Moreover, copper acetate can also be used in catalytic amounts with O<sub>2</sub> serving as the terminal oxidant

    Cp<sub>2</sub>TiCl<sub>2</sub>‑Catalyzed Regioselective Hydrocarboxylation of Alkenes with CO<sub>2</sub>

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    Cp<sub>2</sub>TiCl<sub>2</sub>-catalyzed regioselective hydrocarboxylation of alkenes with CO<sub>2</sub> to give carboxylic acids in high yields has been developed in the presence of <sup><i>i</i></sup>PrMgCl. The reaction proceeds with a wide range of alkenes under mild conditions. Styrene and its derivatives can transform to Îą-aryl carboxylic acids, and aliphatic alkenes can transform to form alkanoic acids

    Density function study transition metal chromium-doped alkali clusters: the finding of magnetic superatom

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    <div><p>The structures, stabilities and magnetic properties of Cr<i>X<sub>n</sub></i> (<i>X</i> = Na, Rb and Cs; <i>n</i> up to 9) clusters are studied using density functional theory to search for the stable magnetic superatoms. The geometrical optimisations indicate the ground-state structures of Cr<i>X<sub>n</sub></i> evolve toward a close packed structure with an interior Cr atom surrounded by <i>X</i> atoms as the cluster size increase. Their stabilities are analysed by the relative energy, gain in energy (Δ<i>E</i>(<i>n</i>)) and the highest unoccupied molecular orbital and lowest unoccupied molecular orbital gaps. Furthermore, the magnetic moments of Cr<i>X<sub>n</sub></i> clusters show an odd–even oscillation. Here, we mainly focus on the Cr<i>X</i><sub>7</sub> (<i>X</i> = Na, Rb and Cs) clusters due to the same valence count as the known stable magnetic superatoms VNa<sub>8</sub>, VCs<sub>8</sub> and TiNa<sub>9</sub>. Although these clusters all have a filled electronic configuration 1S<sup>2</sup>1P<sup>6</sup> and large magnetic moment 5 μ<sub>B</sub>, our studies indicate that only CrNa<sub>7</sub> is highly stable compared to its nearest neighbours, while CrRb<sub>7</sub> and CrCs<sub>7</sub> clusters are less stable. This suggests that Cr-doped Na<sub>7</sub> is most appropriate for filled electronic configuration and CrNa<sub>7</sub> is shown to be a stable magnetic superatom. More interesting, we find CrRb<sub>8</sub> and CrCs<sub>8</sub> with the filled electronic configuration 1S<sup>2</sup>1P<sup>6</sup> have higher stability and large magnetic moment 6 μ<sub>B</sub> in their respective series.</p></div

    Structural and Relative Stabilities, Electronic Properties, and Hardness of Iron Tetraborides from First Prinicples

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    First-principles calculations were carried out to investigate the structure, phase stability, electronic property, and roles of metallicity in the hardness for recently synthesized FeB<sub>4</sub> with various different structures. Our calculation indicates that the orthorhombic phase with <i>Pnnm</i> symmetry is the most energetically stable one. The other four new dynamically stable phases belong to space groups monoclinic <i>C</i>2/<i>m</i>, orthorhombic <i>Pmmn</i>, trigonal <i>R</i>3̅<i>m</i>, and hexagonal <i>P</i>6<sub>3</sub>/<i>mmc</i>. Their mechanical and thermodynamic stabilities are verified by calculating elastic constants, formation enthalpies, and phonon dispersions. We found that all phases are stabilized further under pressure. Above the pressure of about 50 GPa, the formation enthalpy of <i>Pmmn</i> is almost equal to that of <i>P</i>6<sub>3</sub>/<i>mmc</i> phase. The analysis on density of states not only demonstrates that formation of strong covalent bonding in these compounds contributes greatly to their stabilities but also that they all exhibit metallic behavior which does not relate to the approach used. By considering metallic contributions, the estimated Vickers hardness values based on the semiempirical model show that the OsB<sub>4</sub>-structured FeB<sub>4</sub>, with a hardness of 48.1 GPa, well exceeding the limitation of superhardness (40 GPa), is more hard than the most stable phase. The others are predicted to be potential hard materials. Moreover, the atomic configuration and strong B–B covalent bonds are found to play important roles in the hardness of materials

    Four-Component Cascade Heteroannulation of Heterocyclic Ketene Aminals: Synthesis of Functionalized Tetrahydroimidazo[1,2‑<i>a</i>]pyridine Derivatives

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    An efficient and straightforward four-component synthetic protocol has been developed to synthesize imidazo­[1,2-<i>a</i>]­pyridines and imidazo­[1,2,3-<i>ij</i>]­[1,8]­naphthyridine derivatives incorporating medicinally privileged heterosystems from heterocyclic ketene aminals, aldehydes, diketene, and amines via cascade reactions, including diketene ring-opening, Knoevenagel condensation, aza–ene reaction, imine–enamine tautomerization, cyclocondensation, and intramolecular S<sub>N</sub>Ar. This strategy can provide an alternative approach for easy access to the highly substituted imidazo­[1,2-<i>a</i>]­pyridine derivatives in moderate to good yields using four simple and readily available building blocks under mild conditions. Importantly, the unusual splitting peaks in the <sup>1</sup>H NMR spectra of the products derived from heterocyclic ketene aminals with an <i>o</i>-halogen atom on the aryl ring were explained reasonably by varying the temperature in NMR analysis

    Phase Stability, Physical Properties, and Hardness of Transition-Metal Diborides MB<sub>2</sub> (M = Tc, W, Re, and Os): First-Principles Investigations

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    Using first-principles calculations, the structural stability, elastic strength, and formation enthalpies of four diborides MB<sub>2</sub> (M = Tc, W, Re, and Os) are investigated by means of the pseudopotential plane-waves method, as well as the roles of covalency and bond topology in the phase incompressibility. Three candidate structures of known transition-metal diborides are chosen to probe. The calculated lattice parameters, elastic properties, Poisson’s ratio, and <i>B</i>/<i>G</i> ratio are derived. It is observed that the ReB<sub>2</sub>-type structure containing well-defined zigzag covalent chains exhibits an unusual incompressibility along the <i>c</i> axis comparable to that of diamond. Formation enthalpy calculations demonstrate that the ground-state phase is synthesizable at low pressure, whereas the other phase can be achieved through the phase transformation. Moreover, according to Mulliken overlap population analysis, a semiempirical method to evaluate the hardness of multicomponent crystals with a partial metallic bond is presented. The predicted hardness of WB<sub>2</sub>–WB<sub>2</sub>, ReB<sub>2</sub>–ReB<sub>2</sub>, and OsB<sub>2</sub>–OsB<sub>2</sub> is in reasonable agreement with experiment data. Both strong covalency and a zigzag topology of interconnected bonds underlie the ultraincompressibilities. In addition, the superior performance and largest hardness of ReB<sub>2</sub>–ReB<sub>2</sub> indicate that it is a superhard material. This work provides a useful guide for designing novel borides materials having excellent mechanical performances

    Crystal Structures, Stabilities, Electronic Properties, and Hardness of MoB<sub>2</sub>: First-Principles Calculations

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    On the basis of the first-principles techniques, we perform the structure prediction for MoB<sub>2</sub>. Accordingly, a new ground-state crystal structure WB<sub>2</sub> (<i>P</i>6<sub>3</sub>/<i>mmc</i>, 2 fu/cell) is uncovered. The experimental synthesized rhombohedral <i>R</i>3̅<i>m</i> and hexagonal AlB<sub>2</sub>, as well as theoretical predicted RuB<sub>2</sub> structures, are no longer the most favorite structures. By analyzing the elastic constants, formation enthalpies, and phonon dispersion, we find that the WB<sub>2</sub> phase is thermodynamically and mechanically stable. The high bulk modulus <i>B</i>, shear modulus <i>G</i>, low Poisson’s ratio ν, and small <i>B</i>/<i>G</i> ratio are benefit to its low compressibility. When the pressure is 10 GPa, a phase transition is observed between the WB<sub>2</sub>-MoB<sub>2</sub> and the rhombohedral <i>R</i>3̅<i>m</i> MoB<sub>2</sub> phases. By analyzing the density of states and electron density, we find that the strong covalent is formed in MoB<sub>2</sub> compounds, which contributes a great deal to its low compressibility. Furthermore, the low compressibility is also correlated with the local buckled structure
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