Organically modified Pd-silica catalysts applied in Heck coupling

Pd-silica catalysts prepared by depositing Pd onto silica precursors modified by surface methyl or phenyl groups through the reduction of Pd2+ ions with surface Si-H functions exhibit high activity and selectivity in Heck coupling.     

Determination of enantiomeric purity of 1-substituted 3-amino-1,2-dicarba-<Emphasis Type="Italic">closo</Emphasis>-dodecaboranes by HPLC on chiral stationary phases

A determination of enantiomeric purity of 1-substituted (Me, Ph, and Prⁱ) 3-amino-1,2dicarba-closo-dodecaboranes by HPLC on chiral Chiralcel OD-H and Chiralpac AD stationary phases involving preliminary phthaloylation of 3-aminocarboranes has been suggested as a general method.     

Synthesis and chromatographic study of methyl-2,3-O-isopropylidene-5-dimethyl-arsinoyl-β-d-ribofuranoside and methyl-2,3-O-isopropylidene-5-deoxy-5-dimethyl-thioarsinoyl-β-d-ribofuranoside

The synthesis of two riboside-containing arsenic compounds, methyl-2,3-O-isopropylidene-5-dimethyl-arsinoyl-β-d-ribofuranoside and methyl-2,3-O-isopropylidene-5-deoxy-5-dimethyl-thioarsinoyl-β-d- ribofuranoside is presented in this paper. Intermediates and final products of the synthesis were examined by gas chromatography and thin layer chromatography. The purity of the products was assessed by NMR spectroscopy. Trimethylsilylation was used to volatilise sugar compounds and thus use of the costly HPLC–MS technique was avoided. The results affirmed the presence of tautomers in case of arsenosugars.     

Hydrogen bonding in the urea dimers and adenine–thymine DNA base pair: anharmonic effects in the intermolecular H-bond and intramolecular H-stretching vibrations

The equilibrium structures, binding energies, vibrational harmonic frequencies, and the anharmonic corrections for two different (cyclic and asymmetric) urea dimers and for the adenine–thymine DNA base pair system have been studied using the second-order Møller–Plesset perturbation theory (MP2) method and different density functional theory (DFT) exchange–correlation (XC) functionals (BLYP, B3LYP, PBE, HCTH407, KMLYP, and BH and HLYP) with the D95V, D95V**, and D95V++** basis sets. The widely used a posteriori Boys–Bernardi or counterpoise correction scheme for basis set superposition error (BSSE) has been included in the calculations to take into account the BSSE effects during geometry optimization (on structure), on binding energies and on the different levels of approximation used for calculating the vibrational frequencies. The results obtained with the ab initio MP2 method are compared with those calculated with different DFT XC functionals; and finally the suitability of these DFT XC functionals to describe intermolecular hydrogen bonds as well as harmonic frequencies and the anharmonic corrections is assessed and discussed.     

Synthesis of new polyconjugated compounds based on 9,10-diphenylphenanthrene

A procedure was developed for the synthesis of dimethyl 9,10-diphenylphenanthrene-2,7-dicarboxylate, and the latter was used as starting compound for the preparation of 9,10-diphenyl-2,7-bis(2-phenylethenyl) phenanthrene derivatives and 2,7-bis[(E)-2-(1,3-benzoxazol-2-yl)ethenyl]-9,10-diphenylphenanthrene, which showed strong luminescence in the solid state and in solution. Spectral properties of the products were studied.     

From a Network of Computed Reaction Enthalpies to Atom‐Based Thermochemistry (NEAT)

A simple and fast, weighted, linear least‐squares refinement protocol and code is presented for inverting the information contained in a network of quantum chemically computed 0 K reaction enthalpies. This inversion yields internally consistent 0 K enthalpies of formation for the species of the network. The refinement takes advantage of the fact that the accuracy of computed enthalpies depends strongly on the quantum‐chemical protocol employed for their determination. Different protocols suffer from different sources of error; thus, the reaction enthalpies computed by them have “random” residual errors. Since it is much more natural for quantum‐chemical energy and enthalpy results, including reaction enthalpies, to be based on the electronic ground states of the atoms and not on the historically preferred elemental states, and since these two possible protocols can be converted into each other straightforwardly, it is proposed that first‐principles thermochemistry should employ the ground electronic states of atoms. In this scheme, called atom‐based thermochemistry (AT), the enthalpy of formation of a gaseous compound corresponds simply to the total atomization energy of the species; it is always positive, and it reflects the bonding strength within the molecule. The inversion protocol developed and based on AT is termed NEAT, which represents the fact that the protocol proceeds from a network of computed reaction enthalpies toward atom‐based thermochemistry, most directly to atom‐based enthalpies of formation. After assembling a database that consisted of 361 ab initio reactions and reaction enthalpies involving 188 species, collected from 31 literature sources, the following dependable 0 K atom‐based enthalpies of formation, Δ_f${H{{{\rm AT}\hfill \atop 0\hfill}}}$ , all in kJ mol^?1, have been obtained by means of NEAT: H₂=432.07(0), CH=334.61(15), NH=327.69(25), OH=425.93(21), HF=566.13(31), CO=1072.08(28), O₂=493.51(34), CH₂=752.40(21), H₂O=918.05(20), HO₂=694.53(32), CO₂=1597.77(40), CH₃=1209.64(29), NH₃=1157.44(33), C₂H₂=1625.78(40), and CH₄=1641.68(40), in which the uncertainty values given in parentheses represent 95 % confidence intervals. The average deviation of these values from the well‐established active thermochemical tables (ATcT) values is a mere 0.25 kJ mol^?1, with a maximum deviation of 0.7 kJ mol^?1. This shows that the use of a large number of ab initio reaction enthalpies within a NEAT‐type protocol has considerable advantages over the sequential utilization of the ab initio information.