One-pot synthesis of superacid catalytic material SO4/ZrO2-SiO2 with thermostable well-ordered mesoporous structure

A superacid mesostructured catalyst was directly synthesized by adding sulfuric acid to mesoporous zirconia-silica synthesis mixtures, and was characterized by HRTEM, XRD, UV-Vis, nitrogen sorption, NH₃-TPD, and Pyridine-FTIR. The XRD patterns and electron diffraction micrographs of the calcined samples showed the ordered mesoporous structure and tetragonal crystalline in frameworks. The ammonia TPD, pyridine in situ FTIR, and paraffin isomerization illustrated a new acidic property of the samples. The synthesis of the mesoporous materials, which have stable crystalline frameworks, high surface area, and strong acidity, is very likely to have important technological implications for catalytic reactions of large molecules.     

Translational motion inside self-assembled encapsulation complexes

The motion of guests inside a cylindrical self-assembled host is studied through NMR techniques. Small molecules encapsulated alone, such as the gas molecules cyclopropane and butane, are found to exchange locations slowly but measurably on the NMR time scale using 2D techniques. These molecules can move past one another while still inside the capsule. When gases are coencapsulated with longer flexible molecules such as alkanes, less motion is apparent yet these can still slip by one another and folding of the alkanes also can be detected. Activation barriers for these processes are in the range of 15-17 kcal/mol.     

Cyclization and Isomerization Reactionsin Silylhydrazine Chemistry

Summary.  This review describes the synthesis and isomerization reactions of cyclic silylhydrazines. Topics of discussion are the ring expansion of the three-membered Si(SiN₂) to the four-membered (SiN)₂ ring by lithiation of the (SiN₂) ring and by thermal silyl group insertion into the N*N bond, the ring expansion of a three-membered (SiN₂) to a five-membered (CSi₂N₂) ring by SiCH₂ insertion into the Si*N bond, the formation of isomeric four- and six-membered (SiN₂)₂ rings, the synthesis of five- and six-membered silylhydrazine rings, and the expansion of a five-membered (N₂Si₂N)N ring to the isomeric six-membered (SiNN)₂ ring. The mechanisms of the isomerizations are explained by quantum chemical calculations, and the results are verified by crystal structure determinations. Received February 23, 2001. Accepted (revised) April 24, 2001     

The deviating behavior of thiols in nucleophilic trapping reactions of chromiumcarbonyl phenyl complex substituted propargyl cation

The (phenyl)Cr(CO)₃-complex substituted propargyl cation 4 significantly deviates in the chemoselectivity of the nucleophilic attack of thiols from the previously reported planar chiral ortho-substituted arene complexes and furnishes allenyl thioethers 5. This peculiar behavior can be rationalized assuming a subsequent base catalyzed propargyl–allenyl isomerization in acidic medium (!). An X-ray structure analysis of allenyl thioether 5c recrystallized from acetonitrile over weeks reveals that the [2+2] cyclodimer 10 has been formed. Thiolate adds to 5c to give a single diastereomer of the allyl compound 15 in good yield.     

Integration of nitrogen into coronene bisimides

N-Decorated PBIs and CBIs have been synthesized by the combination of Pictet-Spengler condensation and subsequent oxidative aromatization based on highly electron-deficient amino-PBIs. A detailed analysis of their photophysical properties and molecular crystals has shown that the lateral aryl groups appended on the N-heterocycle have a negligible effect on their optical absorptions and electrochemical potentials, but the subtle modification leads to significant variations on arrangement in the solid state.     

Isomerization of 4-Amino-6-tert-butyl-3-methylthio-1,2,4-triazin-5(4H)-one with Base

4-Amino-6-tert-butyl-3-methylthio-1, 2, 4-triazin-5 (4H)-one I, named as Metribuzin1, is an excellent selective herbicide. In the course of studying the reaction of I, we have found an unexpected reaction. We have attempted to prepare 6-tert-butyl- 4-methylamino-3-methylthio-1, 2, 4-triazin-5 (4H)-one II from I with methyl iodide in the presence of sodium hydroxide in aqueous methanol, surprisingly, instead of II the product III 4-amino-6-tert-butyl-3, 4-dihydro-2-methyl-3-thioxo-1, 2, 4-…     

Synthesis of novel rhodium phosphite catalysts for efficient and selective isomerization-hydroformylation reactions

New modular H₈-BINOL-based phosphite ligands have been synthesized. High activity and regioselectivity has been achieved in the rhodium-catalyzed isomerization-hydroformylation of internal olefins. The active catalysts have been characterized by insitu NMR studies.     

Palladium-catalyzed isomerization of (Z)-1-functionalized-4-acetoxy-2-butenes: Solvent and substituent effects

The Pd(PPh₃)₄-catalyzed isomerization of (Z)-1,4-diacetoxy-2-butene, (Z)-1-(t-butyldimethylsilyloxy)-4-acetoxy-2-butene and (Z)-1-(t-butyldiphenylsilyloxy)-4-acetoxy-2-butene affords the corresponding (E)-isomers and 1,2-difunctionalized-3-butenes. In THF, the formation of the (E)-isomers is mainly due to reaction from an η¹-allylpalladium intermediate while an η³-allylpalladium is the main key intermediate in DMF. The time to reach equilibrium between the products and their respective concentrations depend on the nature of the substituents and the solvent.     

微乳液法制备Pt-S2O82-/ZrO2-Al2O3型固体超强酸催化剂及其异构化性能

采用微乳液法负载Pt制备了Pt-S2O82-/ZrO2-Al2O3(Pt-SZA-M)固体超强酸催化剂, 以正戊烷异构化反应为探针, 对比了微乳液法和浸渍法负载Pt制备的催化剂(Pt-SZA)的异构化性能, 并采用XRD, FTIR, BET, TG-DTA, TPR和TEM对催化剂进行了表征. 结果表明, 与Pt-SZA催化剂相比, Pt-SZA-M催化剂中Pt粒子的粒径更小(4.5 nm)且尺寸更均一; Pt-SZA-M催化剂的比表面积(109.6 m2/g)比Pt-SZA催化剂(95.0 m2/g)增加了15.4%. Pt-SZA-M催化剂的初始还原温度比Pt-SZA催化剂降低了10~20℃, 表明微乳液法负载Pt可以提高催化剂的氧化活性, 提高氢分子在催化剂上的吸附解离能力. 异构化活性实验结果表明, 与Pt-SZA催化剂相比, Pt-SZA-M催化剂的低温活性得到明显改善, 在反应压力为2.0 MPa、 氢烃摩尔比为4: 1、 质量空速为1.0 h-1的条件下, Pt-SZA-M催化剂在反应温度为230℃时活性达到60.8%, 在100 h内异戊烷的收率可稳定在58.0%左右, 选择性在95.0%以上.     

A H, C and N NMR spectroscopic and GIAO DFT study of ethyl 5-oxo-2-phenyl-4-(2-phenylhydrazono)-4,5-dihydro-1H-pyrrole-3-carboxylate

¹⁵N-Labelled ethyl 5-oxo-2-phenyl-4-(2-phenylhydrazono)-4,5-dihydro-1H-pyrrole-3-carboxylate was synthesized by azo-coupling of diazotized aniline (using Na¹⁵NO₂ , 99% ¹⁵N) with ethyl 4,5-dihydro-5-oxo-2-phenyl-(1H)-pyrrole-3-carboxylate. The product was formed as a tautomeric hydrazone mixture as confirmed by ¹³C and ¹⁵N chemical shifts, and was obtained as a mixture of E and Z isomers according to ⁿJ(¹⁵N, ¹³C). A comparison of the ¹H NMR data with GIAO DFT calculations enabled determination of the configuration of the carboxy ester group in both isomers.