烯丙醇不对称环氧化新方法

一个新的金属催化的烯丙醇不对称环氧化(asymmetric epoxidation A.E)似比以前所有烯丙醇不对称环氧化方法为好。这个比较简单的新方法引人注意的一个方面是对映选择性非常之高而且所需试剂(+)-或(-)-酒石酸二酯,四异丙氧钛和叔丁基过氧化氢都容易得到。自从 1980年 Sharpless等发现这个方法以     

催化量的氢化钙-硅胶对Sharpless烯丙醇不对称环氧化的影响

1980年,Sharpless发现用他的试剂[Ti-(OiPr)_4,(+)-或(-)-酒石酸和叔丁基过氧化氢]可对烯丙醇进行不对称环氧化。以后该反应广泛地应用于许多光学活性天然产物的     

Sharpless试剂的改良及应用

本文总结了最近改良 Sharpless 烯丙醇不对称环氧化试剂[Ti(OiPr)_4,酒石酸酯]的几种方法,通过在试剂中加入几种催化剂,改变试剂组成或相对含量,优化了反应条件,扩大了试剂的使用范围。     

手性酒石酸酯对不对称环氧化反应动力学拆分DL-1-十四烯-3-醇的催化选择性

利用Sharpless不对称环氧化反应动力学拆分二级烯丙醇DL-1-十四烯-3-醇,研究了不同手性酒石酸酯催化剂[酒石酸乙酯(DET)、酒石酸异丙酯(DIPT)、酒石酸环己酯(DCHT)以及酒石酸环十二酯(DCDT)]对该反应的催化选择性,拆分所得的烯丙醇的光学纯度有一定差异,从90%到99?.     

绣线菊碱C、D关键BCD三环中间体的不对称合成

从易于制备的非手性烯丙醇化合物出发,以经典的的Sharpless不对称环氧化为关键反应构建烯丙仲醇手性中心,共经10步线性步骤以28.6%的总收率首次实现了绣线菊碱C、D全合成路线中BCD三环中间体(-)-4的不对称合成,该合成路线中涉及3个新化合物,其结构经¹H NMR, ¹³C NMR和HR-MS(ESI)表征。     

烯丙醇化合物的不对称环氧化

本文报道了三个脂肪族烯丙醇化合物(1-3)的不对称环氧化反应。由反式烯丙醇2得到的反式烯丙醇环氧化合物2a的对映体过量大于由顺式烯丙醇1得到的环氧化合物1a的对映体过量。叔羟基二取代烯丙醇3经不对称环氧化生成的3a,其对映体过量只有4%。     

不对称氨羟化反应

介绍了Sharpless等人新近发现的不对称氨羟化反应,该反应可将烯烃直接转化成为手性β-氨基醇类化合物。对于有些烯烃,Sharpless不对称氨羟化反应具有高的区域选择性(20:1)和高的对映选择性(>98%e.e.)。     

钯配合物和手性磷酸连续催化的烯丙醇和醛的不对称羰基烯丙基化反应

利用钯配合物/手性磷酸催化剂体系,通过不对称连续催化,实现了烯丙醇和醛的不对称羰基烯丙基化反应.该反应使用廉价易得的烯丙醇底物,在催化量的手性磷酸作用下,以优秀的产率和立体选择性得到了高烯丙醇产物.     

烯烃不对称双羟化及其反应机理的研究进展

本文综述了近年来四氧化锇催化烯烃不对称双羟化及其反应机理的研究进展。Sharpless等对烯烃双羟化机理的透彻研究导致了不对称双羟化方法的优化。     

在氢化钙-硅胶存在下的烯丙醇催化不对称环氧化

自从 Sharpless 不对称环氧化被发现以来,这个反应已被广泛地应用于手性天然产物的合成。最近,Sharpless 及其同工作者又将原方法中使用的等摩尔量四异丙氧基钛和酒石酸酯减少到催化量,并加入3(?)或4(?)分子筛。这一改进可减少敏感性环氧醇产物的破环,使产物易于分离。从而使这个方法变得更为经济简便。我们曾报道过的改良 Sharpless     

溶胶-凝胶法制备(Ca1-xMgx)SiO3陶瓷及其微波介电性能

以硝酸钙、硝酸镁、正硅酸乙酯为先驱体, 利用溶胶-凝胶法合成(Ca1-xMgx)SiO3(x=0.1、0.2、0.3、0.4、0.5)陶瓷粉体, 研究了Mg2+取代Ca2+对陶瓷物相组成、烧结特性以及微波介电性能的影响规律. 结果表明, Mg2+在CaSiO3中的最大固溶度不超过0.2；随着Mg2+对Ca2+取代量的增加, 陶瓷在烧结后的主晶相出现从CaSiO3相向CaMgSi2O6相的转变,陶瓷的烧结特性及介电性能出现先增加后下降的趋势；当x=0.3 时, 陶瓷体中CaSiO3相与CaMgSi2O6相共存, 克服了单相CaSiO3或CaMgSi2O6易成片长大的缺点,有效减少了陶瓷中残留的气孔, 提高烧结体致密性. (Ca0.7Mg0.3)SiO3在1320 益烧结后介电常数为6.62, 品质因数为36962 GHz.     

Preparation of surface molecularly imprinted Ru-complex catalysts for asymmetric transfer hydrogenation in water media

Molecularly imprinted Ru-complex catalysts acting in water were prepared on a SiO(2) surface by molecular imprinting of a SiO(2)-supported Ru-complex using organic polymers as surface matrix overlayers. (R)-1-(o-fluorophenyl)ethanol, which is one of the hydrogenated products of o-fluoroacetophenone, was imprinted on the supported Ru-complex as a template, and an active Ru-complex with a shape-selective reaction space (molecularly imprinted cavity) was prepared inside the wall of the hydrophobic organic polymer matrix overlayers. Structures of the SiO(2)-supported and molecularly imprinted Ru catalysts were characterized by means of solid-state NMR, XPS, XRF, ICP, UV/vis, XAFS, TGA, and SEM. The molecularly imprinted Ru catalysts exhibited fine shape selectivity and enantioselectivity for the asymmetric transfer hydrogenation of o-fluoroacetophenone and its derivatives.     

(1S,2S)-1,2-二苯基乙二胺修饰Ir/SiO2催化苯乙酮及其衍生物不对称加氢（英文）

不添加任何稳定剂,在碱性条件下制备了5%Ir/SiO2催化剂,并用于催化苯乙酮的不对称加氢反应中,详细考察了碱和手性修饰剂种类、氢气压力、反应温度、(1S,2S)-1,2-二苯基乙二胺((1S,2S)-DPEN)浓度对反应的影响.在优化反应条件下,5%Ir/SiO2催化剂表现出较好的反应活性和对映选择性.其中,苯乙酮不对称加氢反应的对映选择性达70%.该催化剂不需要任何稳定剂,制备方法简单,催化性能稳定,通过简单的离心分离即可循环使用.     

六氟化铀与卤化氢气体的反应动力学研究

研究了UF6+HX(HX=HCl, HBr和HI)反应动力学, 结果显示,UF6+HX反应速率随着HCl-HBr-HI次序增加, 在室温下它们的反应速率常数分别为2.32×10^-^6, 6.43×10^-^4, 5.89×10^-^3s^-^1.Pa^-^1。UF6+HCl和UF6+HBr反应的表观活化能分别为11.29和4.18kj/mol。以上反应速率依次增加, 表出活化能依次减小的趋向与HX的键能以HCl-HBr-HI次序减小相符合。     

SiH3+O(3P)反应机理的理论研究

The reaction for SiH3+O(3P) was studied by ab initio method. The geometries of the reactants, intermediates, transition states and products were optimized at MP2/6-311+G(d,p) level. The single point calculations for all the stationary points were carried out at the QCISD(T) /6-311+G(d,p) level using the MP2/6-311+G(d,p) optimized geometries. The results of the theoretical study indicate that the major pathway is the SiH3+O(3P)→IM1→TS3→IM2→TS8→HOSi+H2. The other minor products include the HSiOH+H, H2SiO+H and HSiO+H2. Furthermore, the products HOSi, HSiO and HSiOH(cis) can undergo dissociation into the product SiO. In addition, the calculations provide a possible interpretation for disagreement about the mechanism of the reaction SiH4+O(3P). It suggests that the products HSiOH, H2SiO and SiO observed by Withnall and Andrews are produced from the secondary reaction SiH3+O(3P) and not from the reaction SiH4+O(3P).     

Formation of a nanostructured layer on bioglass particles of different sizes immersed in tris-buffered solution. N2 adsorption and HR-TEM/EDS analysis

Morphological and structural variations of particles of Bioglass with two different grain sizes reacted in Tris-buffered solution were analyzed by means of N(2) adsorption/desorption at 77 K and HR-TEM/EDS. A remarkable increase in specific surface area (ssa) was observed after the first hour of dissolution. A plateau value corresponding to an increase of at least 2 orders of magnitude was reached after 2 days of dissolution. The ssa increase was faster for the smaller particle size sample, and the ratio between the ssa of the starting samples was not maintained during dissolution. Both micro- and mesopores were formed at different stages of the reaction for the two samples. Increasing ssa was also connected to the formation of a microcrystalline structure rich in Ca and P, as shown by TEM images. The segregation of both a SiO(2)-rich amorphous phase and a Ca/P-rich crystalline phase was observed after the first hour of dissolution. After 2 days of reaction, Ca/P-rich particles made of fine aciculate crystals were found either in close contact with SiO(2) particles or deposited on a small SiO(2)-rich core. A preliminary analysis of TEM data showed the formation, together with hydroxy carbonate apatite, of different types of calcium phosphates not detectable by powder X-ray diffraction.     

Cycloaddition of electron-deficient olefins to norbornadiene in the presence of nickel bisphosphine systems

[2+2+2] Cycloaddition of electron-deficient olefins to norbornadiene in the presence of nickel bisphosphine catalysts was studied. The influence of the bisphosphine structure on the regio- and stereoselectivity of the reaction as well as on the yields of the reaction products was investigated. New evidence for the influence of chiral bisphosphine ligands on the enantioselectivity of the reaction was obtained.     

Charge-transfer processes in the assembly of Si(n)O(m) neutral clusters

The chemical bond formation in oxygen-rich Si(n)O(m) clusters was investigated by sampling the potential energy surface of the model systems SiO + SiO(2) → Si(2)O(3) and (SiO)(2) + SiO(2) → Si(3)O(4) along a two-dimensional reaction coordinate, by density functional theory calculations. Evidence for crossing between the weakly bound neutral-neutral (SiO)(n) + SiO(2) and the highly attractive ion-pair (SiO)(n)(+) + SiO(2)(-) surfaces was found. Analysis of frontier molecular orbitals and charge distribution showed that surface crossing involves transfer of valence electron charge from (SiO)(2) to SiO(2). The sum of the natural atomic charges over the (SiO)(n) and (SiO(2)) groups of the Si(n)O(m) cluster products, gave a net positive charge on the (SiO)(n) "core" and a net negative charge on the (SiO(2)) groups. This is interpreted as the "ion-pair memory" left on the Si(n)O(m) products by the charge-transfer mechanism and may provide a way to assess the role of charge-transfer processes in the assembly of larger Si(n)O(m) neutral clusters.     

SiO2在CH3ONO→CH3O+NO解离中作用的理论研究

利用B3LYP方法,在6-31 G^ 基组下研究了在SiO2存在下的CH3ONO→CH3O NO解离反应．计算了全优化下的解离反应,以及固定SiO2的键长和键角做部分优化下的解离反应．在反应中SiO2与CH3ONO相接近,O-N键逐渐伸长,生成复合物,放出热量,进一步促进了CH3ONO中NO的解离．     

Promoter effect on the CO_2-H_2O formation during Fischer-Tropsch synthesis on iron-based catalysts

The effects of Mg,La and Ca promoters on primary and secondary CO2 and H2O formation pathways during Fischer-Tropsch synthesis on precipitated Fe/Cu/SiO2 catalysts are investigated.The chemisorbed oxygen atoms in the primary pathway formed in the CO dissociation steps reacted with co-adsorbed hydrogen or carbon monoxide to produce H2O and CO2,respectively.The secondary pathway was the water-gas shift reaction.The results indicated that the CO2 production led to an increase in both primary and secondary pathways,and H2O production decreased when surface basicity of the catalyst increased in the order Ca Mg La.