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Propane dehydrogenation (PDH) to propene is an important alternative to oil-based cracking processes, to produce this industrially important platform chemical.sup.1,2. The commercial PDH technologies utilizing Cr-containing (refs. .sup.3,4) or Pt-containing (refs. .sup.5-8) catalysts suffer from the toxicity of Cr(vi) compounds or the need to use ecologically harmful chlorine for catalyst regeneration.sup.9. Here, we introduce a method for preparation of environmentally compatible supported catalysts based on commercial ZnO. This metal oxide and a support (zeolite or common metal oxide) are used as a physical mixture or in the form of two layers with ZnO as the upstream layer. Supported ZnO.sub.x species are in situ formed through a reaction of support OH groups with Zn atoms generated from ZnO upon reductive treatment above 550 °C. Using different complementary characterization methods, we identify the decisive role of defective OH groups for the formation of active ZnO.sub.x species. For benchmarking purposes, the developed ZnO-silicalite-1 and an analogue of commercial K-CrO.sub.x/Al.sub.2O.sub.3 were tested in the same setup under industrially relevant conditions at close propane conversion over about 400 h on propane stream. The developed catalyst reveals about three times higher propene productivity at similar propene selectivity. Propene is obtained through propane dehydrogenation using catalysts that are toxic, expensive or demanding to regenerate with ecologically harmful compounds, but the ZnO-based alternative reported here is cheap, clean and scalable., Author(s): Dan Zhao [sup.1] [sup.2] , Xinxin Tian [sup.2] [sup.3] , Dmitry E. Doronkin [sup.4] , Shanlei Han [sup.1] [sup.2] , Vita A. Kondratenko [sup.2] , Jan-Dierk Grunwaldt [sup.4] , [...]

The synthesis of the characterization of a series of dirhenium metallaboranes containing 5-10m boron atoms is described. Competition between main group and transition metal electronic properties is also presented.

The synthesis of the characterization of a series of dirhenium metallaboranes containing 5-10m boron atoms is described. Competition between main group and transition metal electronic properties is also presented.

The density functional theory is utilized to study the bonding and electronic features of the homo- and heterobimetallic sp carbon chain complexes. The diiron and rhenium or iron dications are identified to contain three positions of approximately similar power and clearly specifying the magnetic information for experiments.

B3LYP density functional studies located endohedral dodecahedrane minima and predict their stability toward dissociation. A proton (H(super +)) preferred attachment to the external dodecahedrane surface.

Research has been conducted on the neutral in-plane tris-homoaromaticity. The study of this homoaromaticity in tris(bismethano)benzene has been carried out and the hypothesis that the pi-orbitals might interact in the plane via the unsaturated carbon atoms has been tested and discussed.

Aromaticity of cyclopentafused pyrene congeners has been investigated at various levels of theory. Aromaticity of these compounds decreased with increasing number of externally fused five-membered rings.

The first observation of vibrational structure in the ionization of metal ligand sigma bonding valence orbital, specifically the Re- H sigma-bond ionizations of CpRe(NO)(CO)H and CpRe(NO)(CO)H [Cp = eta(super 5)-C5H5, Cp = eta(super 5)-C5(CH3)5] is reported. The observations suggest that even in low symmetry molecules the orbital corresponding to the Re-H sigma bond and the Re-H vibrational mode is much localized.

A computational study of MO3S9 as a model of amorphous molybdenum trisulfide is presented.

The experimental enthalpy of the formation of triquinacene (1) was increased by 4 kcal/mol after determining it through the measurement of its energy of combustion in a microcalorimeter. The modified enthalpy value contradicts stabilization by homoaromatic interaction. The homoaromaticity of 1 is also indicated by the negligible computed stabilization energy, diamagnetic susceptibility exaltation and nucleus-independent chemical shift values.

Research was conducted to examine the proton chemical shifts and nucleus-independent chemical shifts (NICS) of the (N)phenylenes and related compounds by the GIAO/HF method. Both NICS and proton chemical shifts values demonstrate attenuation of aromatic and antiaromatic character in the six- and four-membered rings. Both proton and NICS shifts of antikekulene indicate only slight additional antiaromatic property.

Syn and anti bismethanol[14]annulenes were used to test the accuracy of the semiempirical (PM3) and ab initio (HF and MP2), as well as density functional theory methods (BLYP and B3LYP). Compared to experimental data, PM3 and HF overemphasized bond localized structures, while the correlated MP2 and density functional methods favored overly delocalized aromatic structures. B3LYP computations gave the best agreement with the available experimental data.

A computational investigation of the aromaticity and antiaromaticity of oligocyclic annelated five-membered ring systems, pentalene, acepentalene and dicyclopenta(cd,gh)pentaline and related compounds was conducted using density functional theory (B3LYP/6-31G*). Results indicate that pentalene, acepentalene and dicyclopenta(cd,gh)pentalene have singlet ground states. Findings also indicate that pentalene and acepentalene are antiaromatic with localized electronic structures while dicyclopental(cd,gh)pentalene is aromatic with a delocalized structure.

The aromaticity and antiaromaticity of charged fluorenyl, indenyl, and cyclopentadienyl systems were evaluated using ab initio computations at high level and density theory. Results showed that fluorenyl, indenyl, and cyclopentadienyl anions were highly aromatic when compared with anthracene, benzene, and naphthalene. Singlet cyclopentadienyl and indenyl cations were found as antiaromatics while fluorenyl cation as non-aromatic. Results also revealed that delocalization energies of aromatic cations were greater than those of the antiaromatic cations.

The homoaromatic characteristics of strained semibullvalenes were established through analyses of high level ab initio and density functional theory aided by UV and 13C NMR spectral studies. Results have shown that the C2 v symmetric transition structure for the Cope rearrangement in the parent semibullvalene was bishomoaromatic. However, the 4,6-ethanosemibullvalene was localized and not homoaromatic.

Polynitrogen molecules were examined systematically at high levels of ab initio and density functional theory. Besides N2, the thermodynamically most stable Nn molecules, located with the aid of a newly developed energy increment system, are all based on pentazole units. The geometric, energetic, and magnetic criteria establish pentazole (2) and its anion (3) to be as aromatic as their isoelectronic analogues. The bond lengths in 2 and 3 are equalized.

The cyclization of 1,3-cis-5-hexatriene to 1,3-cyclohexadiene is accelerated by the complexation of Lithium cation. These electrostatic accelerations are due to higher electrostatic stabilization of the transition structure than the ground state. The electrostatic acceleration effect of the 1,5-hydrogen shift in cyclopentadiene is also generated by the complexation of Na+, Mg2+, HBe+ and Be2+. The acceleration is maximum with Be2+ and minimum with Na+.

A (10)annulene obeys Huckels rule but prefers nonaromatic, nonplanar structure. Second order perturbation and density functional theories help characterize a new aromatic, planar mono-trans isomer of (10)annulene. The geometry of the isomer shows Cs point group with the inward pointing hydrogen bent about 20 degrees from the carbon plane and the carbon-carbon bond lengths are very close to those of benzene. Energetic and magnetic properties support the aromatic character of the isomer, while UV and NMR structural studies reveal ambiguous behavior in the isomer.

The aromatic stability of 3,5-dehydrophenyl cation is due to the presence of two (4n+2)-electron conjugated systems. The cation exhibits higher stability than its cyclic isomers and its open-chain isomers. 2,4,6-trisilyl substitution increases the stability of the cation through hyperconjugation. Magnetic susceptibility exaltation demonstrates the double aromaticity of the cation and of the D6h cyclo(6)carbon. Both compounds have the necessary geometric, energetic and magnetic requirements for aromaticity.

An investigation of the stability of the singlet and triplet states of tetraoxocyclobutane (c4O4, the tetramer of carbon monoxide) at various levels of theory is presented. Second order perturbation favors the singlet state, whereas the triplet and open-shell singlet states are computed to be more stable using the hybrid B3LYP density functional method.

[5]pericyclenes were examined at density functional levels and at high ab initio levels. Results showed that [5]pericyclenes 2 and 5 could not be considered homoaromatic on the basis of magnetic, energetic and geometric criteria. Furthermore, results indicate that these [5]pericyclenes are basically strain free, providing support for the argument in favor of nonhomoaromaticity.

The hyperconjugation effect on the substituted methylboranes (XCH2BH2; X = H, CH3, NH2, PH2, OH, SH, F, Cl, Br ) by employing the ODP approach systematically is investigated.

The Bronsted acidity of isomorphously substituted ZSM-5 by B, AL, Ga, and Fe is investigated at the B3LYP level of density functional theory. In both Al and GA modified clusters, the absorbed NH3 bedoes ammonium (NH(sub 4)(super +) stabilized by two N-H...O hydrogen bonds, while the physisorbed NH3 is stabilized by one N...H-O hydogen bond in Fe and B substituted clusters.

The results of four density-functional processes applied to calculate the C - C homolytic bond dissociation enthalpies (BDE) of a set of aromatic hydrocarbons are presented. The BDE values for large aromatic hydrocarbon systems of interest are calculated and the consequent effects are discussed.

The strategy and design in catalysts and reagents for fluorous and supercritical CO2 chemistry is advanced by clearly identifying the methylene spacer lengths needed for the effective insulation of a typical active site from a perfluoroalkyl chain. Computations show that the first carbon of a perfluoroalkyl segment exhibits a much greater inductive effect than the second, and that ionization potentials of nonfluorinated phosphines P((CH2)mCH3)3 reach a limit at approximately nine carbons (m=8).

A study was conducted to examine the affinity of the all-trans-cyclodecapentaene to the central unit of dodecahedrapentaene in the [n]-trannulenes, a member of the all-trans-[n]annulene family which exhibited in-plane conjugation. The proton nuclear magnetic resonance was performed and the aromaticity of the compound was tested. The findings suggest an inverse relationship between the heat formation and ring size for each CH group for both the aromatic and antiaromatic trannulenes.

It is possible to use magnetic criteria to assess the degree of aromaticity of a series of inorganic ring systems. The homodesmotic reaction can be used to evaluate both aromatic stabilization energy values and exalted magnetic susceptibilities. The nucleus-independent chemical shift (NICS)(delta) and NICS(pi) tend to cancel when delocalization is not present. Cyclic delocalized systems have enhanced NICS(pi) contributions. Both NICS(pi) and NICS(delta) decrease with increase of the ring size (bond length).

The first stable silanethione, Tbt(Tip)Si=S (Tip = 2,4,6-triisopropylphenyl) has been synthesized, using 2,4,6-tris(bis(trimethylsilyl)methyl)-phenyl (Tbt). Tbt was applied to the kinetic stabilization of silaaromatic species, leading to the isolation of 2-silanaphthalene. The structure was confirmed by NMR spectral data.

A novel aromacity/antiaromacity criterion uses absolute magnetic shieldings at ring centers and quantum mechanics programs to determine the aromacity/antiaromacity of a range of five-membered rings. The method corresponds to the popular NMR chemical shift convention and is superior to aromaticity determination through diamagnetic susceptibility exaltation. The negative nucleus-independent chemical shifts (NICS) denote aromaticity whereas positive NICS represent antiaromacity. The antiaromatic 4n pi electron compounds exhibit highly positive NICS.

Ab initio self-consistent reaction field study of the donor-acceptor complexes HCN-BF3 and H3CCN-BF3 reveals that medium effects are responsible for the experimentally observed geometry differences of the complexes in solid and gas states. A crystal dipolar field interaction induces medium effects and only complexes having donor molecules with permanent dipole moment exhibit this effect.

Ab initio calculations predict observed 3He NMR chemical shifts in He at C60 and He at C70. Host fullerene structures influence the calculated 3He chemical shifts. This calculation also predicts 7Li chemical shifts in isostructural Li(+) at C60 and Li(+) at C70. These calculations also prove the aromatic nature of C60.

A study on the 1,3-dipolar cycloaddition chemical reaction and its mechanistic aspects was conducted to analyze in-plane aromaticity pertaining to significant variables in chemical reactions such as substituent and solvent effects. The aim of the study was to add to the knowledge of the factors which determine the energetic parameters of these reactions and their regiochemistry and stereochemistry. Computational techniques and results are discussed.