苯乙酮、氨甲酸酯参与的直接Mannich反应

Mannich反应是有机化学中最重要的碳-碳键形成反应，其产物是合成手性胺的通用中间体。间接Mannich反应使用不稳定的预制烯醇等当体，以未修饰的酮为给体的直接方法将增强Mannich反应的效率。针对低活性苯乙酮、氨甲酸酯参与的直接Mannich反应，研究工作将更具挑战性。 在前期实验中，我们发现Lewis酸-NbCl5可高效催化苯乙酮、芳香醛、芳香胺三组分直接Mannich反应，反应在环境温度下进行，高收率获得Mannich碱。这是以苯乙酮参与的Mannich反应中，实现催化量Lewis酸催化的首次报道。该方法高效且操作简单。但就底物而言，对易去保护、低活性的氨甲酸酯类底物收率较低。我们设想Brønst酸可解决此类底物问题。令人高兴的是，杂多酸可高效催化芳香酮、芳香醛、氨甲酸酯三组分直接Mannich反应，反应在环境温度下进行，高收率获得N-保护的β-氨基酮。该方法底物范围广泛，普适性强且催化剂便宜。 基于杂多酸在苯乙酮、氨甲酸酯为底物直接Mannich反应中的高效性，我们设想杂多酸与功能化的手性有机小分子-手性伯胺组装可解决催化剂回收问题，同时实现不对称催化。实验结果表明，非共价键固载手性伯胺不能有效催化苯乙酮为底物的直接Mannich反应，无论是对映选择性还是收率均较低。随后，我们以丙二酸酯及α-氨基砜为底物，以增强底物活性，同时绕开亚胺的不稳定性。辛可宁伯胺以氢键双活化底物，有效催化原位产生氨甲酸酯类亚胺与丙二酸酯的Mannich反应，高收率获得Mannich碱，ee值中等。 我们采用逐步解决问题的策略解决Mannich反应中的部分问题并在Lewis酸催化、Brønst酸催化、非共价键固载手性伯胺催化及手性伯胺氢键催化的直接Mannich反应中做出了有益探索。 The Mannich reactions are among the most fundamental carbon-carbon bond forming reactions in organic chemistry, and the reaction products are versatile intermediates in the synthesis of chiral amines. The indirect Mannich reaction uses preformed enolate equivalents. However the preformed enolates are unstable. Thus, a direct methodology based on unmodified ketone donors would enhance the efficiency of the Mannich reaction. Especially researches for the directed Mannich reactions of acetophenone, carbamate, which own lower activities, will be more challengeable. In the initial experiments, we found an efficient Lewis acid-NbCl5 which could catalyze three-component Mannich-type reaction of acetophenone, aromatic aldehydes and aromatic amines at ambient temperature in high yields. This is the first report that use catalytic amount of Lewis acid in the Mannich reactions of .acetophenone. The method reported is not only simple to operate but also efficient. However, as far as amines are concerned, the substrates of carbamates which can be deprotected more easily and less reactive than amines give low yields. We envisaged that Brønsted acid would resolve this problem. Pleasingly, heteropoly acids (HPA) efficiently catalyzed one-pot three-component Mannich reactions of aryl aldehydes, aryl ketones, and carbamates at ambient temperature and afforded the corresponding N-protected β-amino ketones in good to excellent yields. This method provides a novel and improved modification of three-component Mannich reactions in terms of a wide scope of aldehydes, ketones and carbamates, economic viability. Based on the high efficiency of heteropoly acids in the Mannich reaction of acetophenone and carbamates, we envisaged that if HPA were combined with functionalized chiral organocatalysts–chiral primary amines the assemblies may be able to act as recoverable asymmetric organocatalysts. The results of exprimentals showed that noncovalently supported heterogeneous chiral primary amine couldn’t effectively catalyze the Mannich reactions which own two the substrate of acetophenone regardless of enantioselectivity and yield. Then, we employed malonates and α-amido sulfones as substrates to enhance reactivity of substrates and circumvent the instability of imines. A moderately enantioselective and highly yield Mannich reaction with in situ generation of carbamate-protected imines from stable α-amido sulfones catalyzed by cinchonine primary amine catalyst was developed. It is noteworthy that cinchonine primary amine can dual activate substrates through H-bond activation and thus promote the reaction. We applied step-by-step-strategy to resolve some problems in the Mannich reactions and did some instructive explorations in Lewis acid catalysis, Brønst acid catalysis, noncovalently supported heterogeneous chiral primary amine catalysis and chiral primary amine as hydrogen-bond catalysis.

Effect of acidity in TS-1 zeolites on product distribution of the styrene oxidation reaction

The role of Bronsted acidity of titanium silicalite zeolite (with different ratios of Si/Ti) in oxidation reactions of styrene has been investigated and discussed. For zeolites with Si/Ti > 42, most of the titanium is in the zeolite framework. These framework titanium species, which act both as the isolated titanium centers and as Bronsted acidity centers (together with the Bronsted acidity produced by the tetrahedral aluminum impurity introduced during synthesis), can catalyze both the epoxidation and the succeeding rearrangement reactions, thus promoting the formation of phenylacetaldehyde. With an increase in the titanium content of the zeolite, titanium will tend to stay outside the zeolite lattice, except for the TiOx nanophases which can be occluded in the zeolite channels or on the external surface. These non-framework titanium species are favorable for the carbon-carbon bond scission, leading to the production of additional benzaldehyde. The catalytic performances of these zeolites with different Si/Ti ratios are correlated here with their structural information by using solid-state NMR and UV-Vis methods. (C) 2003 Elsevier B.V. All rights reserved.

First synthesis of single and mixed alpha-oxo ketene dithioacetals from active methenyl precursors

beta-Dioxodithioate were produced easily from active methenyl precursors, carbondisulfide and RX with potassium carbonate as base. By a selective basic assistant cleavage of a carbon-carbon bond at the beta-dicarbonyl unit of beta-dioxodithioate and the subsequent alkylation with RX/R'X in situ, single or mixed alpha-oxo ketene dithioacetals were, obtained in good yields.

The reactivity of lanthanide alkyl compounds with phenylacetylene: Synthesis and structure of [(Bu(t)Cp)(2)LnC CPh](2) (Ln=Nd, Gd)

[(Bu(t)Cp)(2)LnCH(3)](2) (Ln = Nd, Gd) react with PhC=CH to form the dimeric alkynide-bridged complexes [(Bu(t)Cp)(2)LnC=CPh](2) [Ln = Nd (I), Gd (II)]. Both compounds crystallized from toluene in the monoclinic space group C2/c. The two complexes are homologous, composed of asymmetric metal-alkynide bridges with Nd-C, Gd-C (alkynide) bond lengths of 2.602(4), 2.641(5) (I) and 2.532(6), 2.601(7) Angstrom (II), respectively. The average Nd-C (ring) and Gd-C (ring) distances are 2.746(13) and 2.703(19)Angstrom.

STUDIES OF ELECTROCHEMICAL CATALYTIC REDUCTION REACTIONS OF TETRAPHENYLPORPHINATOCOBALT 1,2-DIBROMOETHANE AND 1,2-DICHLOROETHANE SYSTEMS IN NONAQUEOUS MEDIA

Electrochemical catalytic reactions of tetraphenylporphinatocobalt were studied in DMF and EtCl2 solutions in the presence of 1,2-dibromoethane and 1, 2-dichloroethane utilizing cyclic voltammetry, thin-layer electrochemistry, in situ UV-visible spectroel

APPLICATION OF AN ULTRAMICROELECTRODE IN HOMOGENEOUS CATALYTIC REACTIONS .4. ELECTROCATALYTIC REDUCTION OF ORGANOHALIDES BY METALLOPORPHYRIN AT ULTRAMICROELECTRODE

The electrocatalytic reduction of 1,2-dibromoethane and tetrabromoethane with CoTPP in DMF solutions containing 0.1 M TBAP was investigated at a Pt ultramicroelectrode. The experimental results indicated that CoTPP obviously exhibited catalytic activity for 1,2-dibromoethane and tetrabromoethane. The rate constants of 1,2-dibromoethane and tetrabromoethane in this system were calculated to be 0.14 x 10(3) and 0.5 x 10(2) M-1 S-1, respectively. The reaction mechanism of 1,2-dibromoethane and tetrabromoethane reduction electrocatalysed by CoTPP in 0.1 M TBAP DMF solution is discussed.

Calculation of bulk modulus on carbon nitrides with chemical bond method

The bulk moduli of some superhard materials were calculated by using the chemical bond method. For simple crystals, such as diamonds, c-BN, SiC, Si, BP, and Ge, the calculated results agree with experimental and theoretical values. For crystals of complex structure, such as beta-BC2N crystal and various structural C3N4 crystals, the results indicate that their bulk moduli are large, but do not exceed that of diamond.

A lattice dynamical treatment for the total potential energy of single-walled carbon nanotubes and its applications: relaxed equilibrium structure, elastic properties, and vibrational modes of ultra-narrow tubes

In this paper, we propose a lattice dynamic treatment for the total potential energy of single-walled carbon nanotubes (SWCNTs) which is, apart from a parameter for the nonlinear effects, extracted from the vibrational energy of the planar graphene sheet. The energetics, elasticity and lattice dynamics are treated in terms of the same set of force constants, independently of the tube structures. Based upon this proposal, we have investigated systematically the relaxed lattice configuration for narrow SWCNTs, the strain energy, the Young's modulus and Poisson ratio, and the lattice vibrational properties with respect to the relaxed equilibrium tubule structure. Our calculated results for various physical quantities are nicely in consistency with existing experimental measurements. In particular, we verified that the relaxation effect makes the bond length longer and the frequencies of various optical vibrational modes softer. Our calculation provides evidence that the Young's modulus of an armchair tube exceeds that of the planar graphene sheet, and that the large diameter limits of the Young's modulus and Poisson ratio are in agreement with the experimental values of graphite; the calculated radial breathing modes for ultra-narrow tubes with diameters ranging between 2 and 5 angstrom coincide with the experimental results and the existing ab initio calculations with satisfaction. For narrow tubes with a diameter of 20 angstrom, the calculated frequencies of optical modes in the tubule's tangential plane, as well as those of radial breathing modes, are also in good agreement with the experimental measurements. In addition, our calculation shows that various physical quantities of relaxed SWCNTs can actually be expanded in terms of the chiral angle defined for the corresponding ideal SWCNTs.

Synthesis and characterization of carbon black supported Pt-Ru alloy as a model catalyst for fuel cells

A set of bimetallic Pt-Ru catalysts prepared by co-impregnation of carbon black with ruthenium(III) chloride hydrate and hydrogen hexachloroplatinate(IV) hydrate were investigated by temperature-programmed reduction (TPR), chemisorption of hydrogen, transmission electron microscopy (TEM), microcalorimetry of adsorbed CO and a structure-sensitive reaction (n-hexane conversion). The results showed that the volumetric capacities for CO and H-2 adsorption is influenced in the bimetallic Pt-Ru catalysts by the formation of a Pt-Ru alloy. The n-hexane reaction revealed that the reaction mechanism for the pure Pt catalyst mainly occurs via cyclic isomerization and aromatization due to the presence of bigger Pt surface ensembles, whereas the Pt-Ru catalysts exhibited predominantly bond-shift isomerization by the diluting effect of Ru metal addition. The differential heats of CO chemisorption on Pt-Ru catalysts fell between the two monometallic Pt and Ru catalysts extremes. (C) 2004 Elsevier B.V. All rights reserved.

Copper(I)-Catalyzed Aryl Bromides To Form Intermolecular and Intramolecular Carbon-Oxygen Bonds

A highly efficient Cu-catalyzed C-O bond-forming reaction of alcohol and aryl bromides has been developed. This transformation was realized through the use of copper(I) iodide as a catalyst, 8-hydroxyquinoline as a ligand, and K3PO4 as a base. A variety of functionalized substrates were found to react under these reaction conditions to provide products in good to excellent yields.

In-situ Fourier transform infrared spectroelectrochemistry as a probe of the glassy carbon electrode chemically modified by nickel (II)-cyanometallates

A new nickel (II)-cyanometallates modified on glassy carbon electrode was prepared by a new method and studied by cyclic voltammetry and in situ Fourier transform infrared (FTIR) spectroelectrochemistry. It was found that the NiHCF film existed in two forms: Ni2Fe(II)-(CN)(6) and M2NiFe(II)(CN)(6), Fe(CN)(3)(6-) codeposited in the NiHCF film existing in free cation or bridged-bond state depended on the property of the cations in electrolyte: in NaCl and LiCl solution, it is in bridges-bonded, but in HCl and KCl, it is free.

SURFACE CHARACTERIZATION OF COBALT TETRAPHENYLPORPHYRIN MODIFIED GLASSY CARBON ELECTRODE BY XPS

Surface structure of the glassy carbon surface modified with cobalt tetraphenyl-porphyrin (CoTPP) by thermal-treatment has been studied by XPS, DTA and TG. During the thermal treatment a bond can be formed between the glassy carbon surface and TPP. Therefore the stability of electrode for the catalysis of dioxygen reduction is improved. Upon thermal treatment at 600 degrees C, FWHM of Co(2p(2/2)) is broadened, the reason is due to overlapping of peaks of multiple states, the spin orbit separation between Co (2p(1/2)) and Co (2p(3/2)) increases to 15.5-16.3eV, which indicated a change from low spin divalent states, the kinetic energy of Co L3VV Auger line and Auger parameter also increase. These changes of central cobalt ion provide a suitable redox potential for Co(III)/Co(II) which is related to the activity for catalysis of dioxygen reduction.

INVESTIGATION OF MICROSTRUCTURE AT IRON TETRAPHENYLPORPHYRIN MODIFIED CLASSY CARBON ELECTRODE BY XPS

Microstructure of the glassy carbon surface modified with iron tetraphenyfporphyrin (FeTPP) by heat treatment has been studied by XPS,, DTA and TG. XPS spectra of Fe 2P_3\2 level in FeTPP and iron tetraphenylporphyriu/glassy carbon (FeTPP/GC) have shown that a bond can be formed between the glassy carbon surface and both the central metal iron ion and the macrocyclic, ligand, which loses its four phenyl groups during the beat treatment. The relationship between the surface mierostructure of FeTPP/GC and the...