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61.
Kinetic studies of the aminolysis of [methyl(thiomethyl)carbene]pentacarbonyl chromium(0),(CO)5CrC(CH3)(SCH3) (1-Cr(S)) and [methyl(thiomethyl)carbene]pentacarbonyltungsten(0), (CO)5WC(CH3)(SCH3) (1-W(S)), with morpholine, a secondary amine, in 50% acetonitrile-50% H2O (v/v at 25 °C) is reported. The second-order rate constant (kA in m−1 s−1) increases with amine concentration, giving a linear dependence with an intercept on the rate axis and a tendency towards leveling off at higher amine concentration. The reaction was found to undergo general base catalysis. The mechanism proposed is very similar to those for ester reactions, involving a nucleophilic addition of amine to the substrate to yield a zwitterionic tetrahedral intermediate in the first step, followed by deprotonation to form in the second step, which, in the third step, converted to product by H2O and/or conjugate acid of the base (BH+), assisted MeS− expulsion. The reactivity (k1) of 1-W(S) was found to be higher than that of 1-Cr(S), whereas, comparable , water catalyzed and , BH+ catalyzed, leaving group departure were found for both the carbenes complexes. All these observations have been explained successfully. 相似文献
62.
Gejihu De Weiping Qin Jisen Zhang Yan Wang Chunyan Cao Yang Cui 《Journal of solid state chemistry》2006,179(3):955-958
In this work, we used the hydrothermal method to synthesize Eu3+ ion-doped cubic BaF2 nanorods, which is a luminescent material. The clubbed structures were well crystallized and exhibited face-centred cubic structures, as indicated by powder X-ray diffraction, scanning electron microscopy, electron diffraction, and transmission electron microscopy. The luminescent properties were studied, and local symmetry surrounding Eu3+ ions and electronic transition processes included. The results indicated that Eu3+ occupied only one C4ν site in nanorods. 相似文献
63.
The benzamide-derived P,O-ligands efficiently promoted the Pd-catalyzed Suzuki cross-coupling reactions of aryl bromides with phenylboronic acid at 0.01 mol % of Pd loading at 60-80 °C to form biaryls in excellent yields. A sterically hindered arylboronic acid gave a quantitative yield of the coupling product at 110 °C with 1 mol % Pd. 相似文献
64.
Addition and Substitution Reactions at Tetrafluoro- and Tetrachlorodiborane(4) From equimolar mixtures of B2F4 and MenN(SiMe3)3-n (n = 0–3) the mono-addition products 1–4 are formed at low temperatures. By elimination of Me3SiF the adduct 2 gives the dimeric monosubstituted diborane 8 , which slowly decomposes at room temperature to the aminoborane 6 and (BF)n. The course of the reactions was studied by means of 11B and 19F NMR spectroscopy and by measuring the vapor pressures. According to the 11B and 31P NMR spectra the reaction of B2Cl4 with PCl5 or [Me4N]Cl in liquid hydrogen chloride at 0°C does not yield [PCl4]2+[B2Cl6]2? or [Me4N]2+[B2Cl6]2? but gives [PCl4]+[BCl4]?, PCl3 and BCl3 or [Me4N]+[BCl4]? and BCl3 besides (BCl)n. 相似文献
65.
1-Benzoyl-4,6-dibromo-3-methyl-1,4,5,6-tetrahydrocyclopenta[c]pyrazole (2) was used as a precursor for o-quinodimethane 3, which was trapped by in situ reactions with dienophiles to give bridged pyrazole derivatives. 相似文献
66.
Wandrey C 《Chemical record (New York, N.Y.)》2004,4(4):254-265
Redox reactions are still a challenge for biochemical engineers. A personal view for the development of this field is given. Cofactor regeneration was an obstacle for quite some time. The first technical breakthrough was achieved with the system formate/formate dehydrogenase for the regeneration of NADH2. In cases where the same enzyme could be used for chiral reduction as well as for cofactor regeneration, isopropanol as a hydrogen source proved to be beneficial. The coproduct (acetone) can be removed by pervaporation. Whole-cell reductions (often yeast reductions) can also be used. By proper biochemical reaction engineering, it is possible to apply these systems in a continuous way. By cloning a formate dehydrogenase and an oxidoreductase "designer bug" can be obtained where formate is used instead of glucose as the hydrogen source. Complex sequences of redox reactions can be established by pathway engineering with a focus on gene overexpression or with a focus on establishing non-natural pathways. The success of pathway engineering can be controlled by measuring cytosolic metabolite concentrations. The optimal exploitation of such systems calls for the integrated cooperation of classical and molecular biochemical engineering. 相似文献
67.
Donna M. Brestensky Thomas R. Hoye Christopher W. Macosko 《Journal of polymer science. Part A, Polymer chemistry》1995,33(12):1957-1967
Anionic living polymerization methods, using organometallic initiators such as butyllithium reagents, have proven useful for, inter alia, styrene polymerization and are amenable to subsequent functionalization of poly(styryl)lithium in the termination step. In this study, general methods for the selective preparation of small styrene oligomers and termination of the intermediate oligo(styryl)lithium anions were investigated. The crude reaction mixtures were analyzed directly by tandem gas chromatography/mass spectrometry (GC/MS). Of the carbon- and silicon-based electrophiles tested, chloro(chloroalkyl)silanes, Cl-SiR2(CH2)nCl in particular, were shown by GC/MS to be regioselective end-capping reagents, thus allowing subsequent transformation to the primary amine. The combined GC/MS data allow not only an estimate of the degree of functionalization, but also the identification of by-products, thus providing insight into the end-capping process that otherwise might be difficult to access. © 1995 John Wiley & Sons, Inc. 相似文献
68.
Micha? K. Cyrański Paul von Ragué Schleyer Tadeusz M. KrygowskiHaijun Jiao Georg Hohlneicher 《Tetrahedron》2003,59(10):1657-1665
The stability of a set of 105 five-membered π-electron systems (involving aromatic, non-aromatic and anti-aromatic species) was evaluated using six isodesmic reactions of which two belong to the subclass of homodesmotic reactions, which are based on cyclic and acyclic reference systems. We demonstrate that the ‘Resonance Energies’ derived from isodesmotic schemes have obvious flaws and do not correct or cancel other contributions to the energy, such as the changes of hybridization, homoconjugation of heterosubstituted cyclopentadienes, conjugative interactions of CC or CX (X=N or P) with a π or pseudo π orbital at Y (Y=O, S, NH, PH), strain, etc. as effectively as possible. Likewise, ‘aromatic stabilization energies (ASE)’ derived from homodesmotic schemes based on the acyclic reference compounds do not give satisfactory results. We strongly recommend that only cyclic reference compounds should be used for ASE and other aromaticity evaluations. The analysis is based on ab initio optimized geometries at B3LYP/6-311+G∗∗. 相似文献
69.
Andrea Basso 《Tetrahedron letters》2004,45(3):587-590
Intramolecular Ugi reactions with bicyclic β-amino acids have been performed and the effects of the configuration and N-alkylation have been studied. We have proven that preferential ring contraction or nucleophilic attack by the solvent depend not only on the presence of N-alkylation but also on the relative disposition of the carboxyl group and the amine. Excellent results in terms of stereoselectivity have been obtained in the case of N-alkyl-3-exo-amino-7-oxabicyclo[2.2.1]-2-endo-carboxylic acids. 相似文献
70.
Six isotypic R6ZTe2 phases have been synthesized in Ta at elevated temperatures and characterized by single crystal X-ray refinements for R=Y, Z=Rh, Pd, Ag, Y and for R=Lu, Z=Cu, Ag. All crystallize in the Sc6PdTe2-type structure, Pnma, Z=4, a∼21.5 Å, b∼4.1 Å, c∼11.4 Å. The results can be viewed as the replacement of Te3 atoms in the parent isotypic Sc2Te (or in the hypothetical Y2Te or Lu2Te analogues) by the above the Z, the Y example giving the new binary phase Y7Te2. The shorter (and stronger) metal-metal bonds concentrate in the region of metal (Z, Y) substitution, as revealed by larger integrated crystal orbital Hamilton population (ICOHP) values derived from linear muffin-tin-orbital (LMTO) calculations. Partial densities-of-states data for Y7Te2 reflect a similar behavior. Individual R-R bond distances are seen to deviate appreciably from the more fundamental overlap population measures for each. 相似文献