17 research outputs found
Rh(III)-Catalyzed Cascade Oxidative Olefination/Cyclization of Picolinamides and Alkenes via CâH Activation
RhÂ(III)-catalyzed
cascade oxidative alkenylation/cyclization of
picolinamides and alkenes to furnish pyrido pyrrolone derivatives
is described, in which three CâH bonds and one NâH bond
broke, while one CâC bond and one CâN 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: CoâBenzene, CoâPyridine, and CoâPyrimidine
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 Coâorganic complexes mainly
arises from the 3d/4s electrons of the cobalt atoms and the Ď-cloud
of the organic molecules. More importantly, we presented an approach
to map and analyze the Coâorganic interactions from another
perspective. The scatter plots of the reduced density gradient (RDG)
versus Ď 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
A variety of alkenylzirconocenes
were efficiently carboxylated
by CO<sub>2</sub> utilizing the (IMes)ÂCuCl 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 CâH Activation
RhÂ(III)-catalyzed
cascade oxidative alkenylation/cyclization of
picolinamides and alkenes to furnish pyrido pyrrolone derivatives
is described, in which three CâH bonds and one NâH bond
broke, while one CâC bond and one CâN 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>âCatalyzed Regioselective Hydrocarboxylation of Alkenes with CO<sub>2</sub>
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
<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 (Î<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 oddâeven 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 Îź<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 Îź<sub>B</sub> in their respective series.</p></div
Structural and Relative Stabilities, Electronic Properties, and Hardness of Iron Tetraborides from First Prinicples
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>3Ě
<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 BâB 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[1,2â<i>a</i>]pyridine Derivatives
An efficient and straightforward four-component synthetic
protocol
has been developed to synthesize imidazoÂ[1,2-<i>a</i>]Âpyridines
and imidazoÂ[1,2,3-<i>ij</i>]Â[1,8]Ânaphthyridine derivatives
incorporating medicinally privileged heterosystems from heterocyclic
ketene aminals, aldehydes, diketene, and amines via cascade reactions,
including diketene ring-opening, Knoevenagel condensation, azaâene
reaction, imineâenamine tautomerization, cyclocondensation,
and intramolecular S<sub>N</sub>Ar. This strategy can provide an alternative
approach for easy access to the highly substituted imidazoÂ[1,2-<i>a</i>]Âpyridine 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
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,
Poissonâs 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>âWB<sub>2</sub>, ReB<sub>2</sub>âReB<sub>2</sub>, and OsB<sub>2</sub>âOsB<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>âReB<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
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>3Ě
<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 Poissonâs 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>3Ě
<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