酸催化及竞争吸附对CeY分子筛吸附脱硫性能的影响

采用液相离子交换(LPIE)法制备了CeY分子筛,并研究烯烃和芳烃对其吸附脱硫性能的影响. 利用固定床穿透曲线技术研究吸附剂的脱硫性能,结果表明：烯烃和芳烃的存在均导致吸附剂吸附硫容量减少,然而,烯烃的影响明显强于芳烃. 采用原位傅里叶变换红外(FTIR)光谱技术研究噻吩、环己烯和苯的吸附行为,结果发现：烯烃和芳烃降低吸附剂脱硫性能的实质分别为吸附剂表面酸性导致的酸催化反应和π-络合吸附的芳烃分子与硫化物分子的竞争吸附. 另外,烯烃的影响取决于吸附剂的表面酸性,尤其是强B酸(Brönsted 酸)中心.这是由于B酸中心会导致烯烃和噻吩发生质子化反应,且质子化物种易于进一步发生低聚反应. 生成的低聚物覆盖吸附活性中心导致吸附剂对其它噻吩分子的吸附能力降低.     

Metal Olefin Complexes: Revisiting the Dewar−Chatt−Duncanson Model and Deriving Reactivity Patterns from Carbon‐13 NMR Chemical Shift

Metal olefin complexes that are ubiquitous intermediates in catalysis are investigated by a detailed analysis of their ¹³C‐NMR chemical shift tensors. This analysis allows evidencing specific electronic features, namely the olefin‐to‐metal σ‐donation and the metal‐to‐olefin π‐backdonation as proposed in the Dewar?Chatt?Duncanson model. Apart from these interactions, the chemical shift tensor analysis reveals an additional ligand‐to‐metal π‐donation of the olefin σ(C=C) orbital in systems with suitably oriented vacant d‐orbitals. This interaction which is not accounted for in the Dewar?Chatt?Duncanson model explains the reactivity of this type of metal olefin complexes towards oxidative cyclization (olefin insertion) and protonolysis.     

工业Fe-Mn催化剂上基于详细反应机理的F-T合成动力学模型Ⅱ.不同校正方法的动力学模型分析

 通过平衡闪蒸模拟催化剂孔道液体组成、烯烃物理吸附和虚拟烯烃分压等方法,考察了化学反应以外的非本征因素对F-T合成动力学模型的校正. 平衡闪蒸模拟催化剂孔道中烯烃组成的校正计算结果表明,在烯烃浓度出现峰值前,溶解度效应对烯烃再吸附及参与二次反应起主导作用,而在烯烃浓度出现峰值后,烯烃的扩散和物理吸附等效应可能起主导作用. 分析烯烃添加的反应器模拟结果发现,考虑烯烃物理吸附作用的动力学模型校正方法不能够正确反映烯烃添加实验的定性规律,而虚拟烯烃分压校正方法能够正确反映烃分布规律并可定量预测烯烃添加对产物分布规律的影响,这对需要尾气循环的F-T合成工业操作具有重要意义.     

Copper(I) nitrile complexes,part III. Reversible olefin complex formation with acetonitrilecopper(I) trifluoromethanesulfonate

Summary Acetonitrilecopper(I) trifluoromethanesulfonate, CuTAN, reversibly forms liquid olefin complexes of composition olefin:CuTAN and olefin: (CuTAN)₂. The complex formation constants of CuTAN with cyclohexene in anisole have been studied based on the observation that CuTAN exists as a dimer in anisole.     

Nanocomposite membranes containing positively polarized gold nanoparticles for facilitated olefin transport

Positively polarized gold nanoparticles have been demonstrated for use as stable olefin carriers for facilitated olefin transport membranes. The formation and size of gold nanoparticles stabilized by 4-dimethylaminopyridine (DMAP) were monitored using X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–visible spectroscopy. Nanocomposite membranes that deliver high separation performance for olefin/paraffin mixtures were prepared by dispersing gold nanoparticles stabilized by DMAP in a polymer matrix, poly(vinyl pyrrolidone) (PVP). X-ray photoelectron spectroscopy (XPS) and zeta potential measurements revealed that gold nanoparticles stabilized by DMAP exhibited a high positive polarity, which is responsible for the reversible interaction between the gold nanoparticles and olefin molecules. Compared to neat PVP membranes, the composite membranes consisting of PVP and the polarized gold nanoparticles showed stable and enhanced separation of olefin/paraffin mixtures.     

Olefin Recovery by *BEA-Type Zeolite Membrane: Affinity-Based Separation with Olefin−Ag+ Interaction

Ag⁺ was introduced into *BEA-type zeolite membrane by an ion-exchange method to enhance olefin selectivity. Ag−*BEA membrane exhibited superior olefin separation performance for both ethylene/ethane and propylene/propane mixtures. Particularly, the separation factor for ethylene at 373 K reached 57 with the ethylene permeance of 1.6×10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹. Adsorption properties of olefin and paraffin were evaluated to discuss contribution of Ag⁺ to separation performance enhancement. A strong interaction between olefin and Ag⁺ in the membrane caused preferential adsorption of olefin against paraffin, leading to selective permeation of olefin. Ag−*BEA membrane also exhibited high olefin selectivities from olefin/N₂ mixtures. The affinity-based separation through Ag−*BEA membrane showed a high potential for olefin recovery and purification from various gas mixtures.     

Calorimetric investigation of the reaction of 1,5-cyclooctadiene with complexes of the type (acac)M(olefin)2 [M = Rh(I), Ir(I)]

The enthalpies of reaction of the complexes (acac)M(olefin)₂ (acac=acetyl-acetonate, M=Rh(I), Ir(I); olefin=ethylene, propene, vinyl chloride, vinyl acetate, methyl acrylate and styrene) with 1,5-cyclooctadiene in n-heptane, according to the reaction [(acac)M(olefin)₂ + 1,5COD → (acac)M(1,5COD) + 2 olefin]_n.heptane have been determined by solution calorimetry. From these results the influence of substituent R in the olefin CH₂CHR on the M---(CH₂CHR) displacement enthalpy has been derived. It is concluded that π back-bonding is slightly more important in the Ir---olefin bond than in the Rh---olefin bond. Furthermore, the data show that, as a result of steric factors which inhibit the approach of solvent molecules, solvation enthalpies are not additive.     

Etudes sur le mecanisme de la metathese des olefines : IV. Echanges d'hydrure et carbenes

The possibility of exchanging hydrogen atoms between the catalyst and the substrate in olefin metathesis was examined. Exchange was observed at a high catalyst/olefin ratio, although virtually no exchange was observed at low ratio, Alkylidenetungsten, formed from WCl₆ and dimetallic derivatives of methane (i.e. CH₂M₂), proved to be efficient catalysts for olefin metathesis. It was concluded from these experiments and from those described earlier that olefin metathesis takes place by addition of an alkylidenetungsten to an olefin followed by fission of the resulting cyclobutane. A solution was proposed to the question raised by the Chauvin mechanism, namely the initiation, which was linked to the formation of alkyltungsten by addition of alkyl- or hydrido-tungten to olefins, followed by appropriate transformation to alkylidenetungsten compounds.     

Diastereoselective Synthesis of Polysubstituted Piperidines through Visible-Light-Driven Silylative Cyclization of Aza-1,6-Dienes: Experimental and DFT Studies

A visible-light-driven radical silylative cyclization of aza-1,6-dienes featuring an acrylonitrile or acrylate moiety and an electron-neutral olefin was developed, which allows for stereoselective synthesis of densely functionalized piperidines in a highly atom-economical manner. Depending on the substitution pattern of the electron-neutral olefin, poor-to-excellent diastereoselectivity was observed. It was suggested that the 6-exo-trig cyclization was initiated by a chemoselective addition of silyl radical toward electron-deficient olefin and the geometry of the remaining olefin is closely associated with the cis-stereoselectivity. DFT calculations supported that a transition state with a cyano group locating at the axial position of the forming piperidine ring might be involved, in which either the increase of 1,3-diaxial repulsion or the lack of hydrogen bonding interaction will diminish diastereoselectivity.     

Photoinduced unzipping depolymerization of poly(olefin sulfone)s possessing photobase generator and base amplifier

The photoinduced depolymerization of poly(olefin sulfone)s was investigated. Poly(olefin sulfone)s possessing base‐amplifying groups were synthesized. A photobase‐generating compound was mixed with poly(olefin sulfone)s and irradiated with 254 nm UV light. The decomposition ratio was significantly enhanced in poly(olefin sulfone)s that possessed base‐amplifying groups. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 602–613, 2009     

A Remarkable cis‐ and trans‐Spanning Dibenzylidene Acetone Diphosphine Chelating Ligand (dbaphos)

A multidentate and flexible diolefin–diphosphine ligand, based on the dibenzylidene acetone core, namely dbaphos ( 1 ), is reported herein. The ligand adopts an array of different geometries at Pt, Pd and Rh. At Pt^II the dbaphos ligand forms cis‐ and trans‐diphosphine complexes and can be defined as a wide‐angle spanning ligand. ¹H NMR spectroscopic analysis shows that the β‐hydrogen of one olefin moiety interacts with the Pt^II centre (an anagostic interaction), which is supported by DFT calculations. At Pd⁰ and Rh^I, the dbaphos ligand exhibits both olefin and phosphine interactions with the metal centres. The Pd⁰ complex of dbaphos is dinuclear, with bridging diphosphines. The complex exhibits the coordination of one olefin moiety, which is in dynamic exchange (intramolecular) with the other “free” olefin. The Pd⁰ complex of dbaphos reacts with iodobenzene to afford trans‐[Pd^II(dbaphos)I(Ph)]. In the case of Rh^I, dbaphos coordinates to form a structure in which the phosphine and olefin moieties occupy both axial and equatorial sites, which stands in contrast to a related bidentate olefin, phosphine ligand (“Lei” ligand), in which the olefins occupy the equatorial sites and phosphines the axial sites, exclusively.     

Titanium reduction in a soluble ziegler—natta catalyst

The spontaneous reduction of Ti^IV to Ti^III in soluble Ziegler—Natta catalysts of type Cp₂RTiCl·R’AlCl₂ (Cp = h⁵ -cyclopentadienyl, R and R’ = methyl or ethyl) was studied both spectrally and chromatographically. Varied were R, R’, Al/Ti ratio, total concentration, solvent, and added olefin. Kinetic order in [Ti] could be varied from zero to second order by changing solvent. This can be explained by a mechanism in which a Cp₂ RTiCl—R’AlCl₂—olefin complex forms in the rate determining step and ligand R is expelled as half alkane half olefin. The expelled olefin may either polymerize or catalyze reduction by forming the rate-determining complex. Different apparent kinetic orders arise from differences in the olefin competitive reactions. The reaction products appear to form in a rapid bimolecular reaction following the rate-determining step. Evidence is presented that neither free radicals nor Cp₂RR’Ti are reduction intermediates. The intermediate is postulated to be a Ti^IV transient hydride formed by a reverse insertion step.     

Palladium/chiral phosphine–olefin complexes: X-ray crystallographic analysis and the use in catalytic asymmetric allylic alkylation

X-ray crystallographic studies on π-allylpalladium complexes coordinated with a chiral phosphine–olefin ligand (−)-1b demonstrate that the phosphine ligand shows a larger trans-influence than the π-bound olefin. The palladium/chiral phosphine–olefin complex efficiently catalyzed asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate with 96% enantioselectivity.     

Thermal degradation of poly(olefin sulphone)s. Part I—The effect of olefin structure on the yields of volatile products

The rates and mechanisms of the thermal degradation of nine alternating poly(olefin sulphone)s with different olefin structures have been investigated at 150°C and 200°C by a novel technique which is particularly suitable for studying the initial steps of the degradation. Rapid degradation was initiated at the CS bond with depolymerisation to sulphur dioxide and olefin. The rate of thermal degradation showed a moderate correlation with the ceiling temperature for monomer-polymer equilibrium and also with the number of β-hydrogen atoms, but neither parameter provided an adequate measure of the sensitivity of all the poly(olefin sulphone)s to thermal degradation. Substantial isomerisation was observed in the formation of olefin from poly(3-methyl-1-butene sulphone).     

Fine‐Tuning the Reactivity and Stability by Systematic Ligand Variations in CpCoI Complexes as Catalysts for [2+2+2] Cycloaddition Reactions

CpCo^I‐olefin‐phosphite and CpCo^I‐bisphosphite complexes were systematically prepared and their reactivity in [2+2+2] cycloaddition reactions compared with highly active [CpCo(H₂C?CHSiMe₃)₂] ( 1 ). Whereas 1 is an excellent precursor for the synthesis of [CpCo(olefin)(phosphite)] complexes ( 2 a – f ), [CpCo(phosphite)₂] complexes ( 3 a – e ) were prepared photochemically from [CpCo(cod)]. The complexes were evaluated in the cyclotrimerization reaction of diynes with nitriles yielding pyridines. For [CpCo(olefin)(phosphite)], as well as some of the [CpCo(phosphite)₂] complexes, reaction temperatures as low as 50 °C were sufficient to perform the cycloaddition reaction. A direct comparison showed that the order of reactivity for the complex ligands was olefin₂>olefin/phosphite>phosphites₂. The complexes with mixed ligands favorably combine reactivity and stability. Calculations on the ligand dissociation from [CpCo(olefin)(phosphite)] proved that the phosphite is dissociating before the olefin. [CpCo(H₂C?CHSiMe₃){P(OPh)₃}] ( 2 a ) was investigated for the co‐cyclization of diynes and nitriles and found to be an efficient catalyst at rather mild temperatures.     

Kinetics of Ag+ contained polymeric complex membranes for facilitated olefin transport

The reactions of silver ion complexes with polyethylene-graft-poly(acrylic acid) (PE-g-AA) and the olefin reversible coordinates with the PE-g-AA–Ag⁺ complex membranes were studied. Infrared and nuclear magnetic resonance spectra confirmed the complex formation between the carboxylic acid of the PE-g-AA and the Ag⁺ ion. Also, the Ag⁺ ion in PE-g-AA-Ag⁺ membrane was assumed to be a fixed carrier that adsorbs and transports olefin, thereby causing a selective olefin/paraffin separation. A theoretical model of the PE-g-AA-Ag⁺ (olefin) complex was proposed. The coordination number of Ag⁺ ion binding to the carboxylic acid of PE-g-AA is about 1.6 in glycerol solution. The coordination number of olefin binding to the Ag⁺ in the PE-g-AA–Ag⁺ complex membrane is 1. Moreover, the kinetics of olefin binding to the PE-g-AA–Ag⁺ complex membranes were studied. The equilibrium, association, and dissociation constants were also presented. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 909–917, 1997     

Ligandbewegungen in űbergangsmetallkomplexen XI 1H-NMR-spektroskopische untersuchungen an acetylacetonat-bis(olefin)-rhodium(I)-komplexen

The temperature-dependent ¹H NMR spectra of acetylacetonatebis(ethylene)-rhodium, (acac)Rh(C₂H₄)₂ (I), of some related complexes containing methoxy-substituted ethylenes have been measured in toluene-d₈ solution. Both monosubstituted [(acac)Rh(C₂H₄)(olefin), olefin = tetramethoxyethylene (II), $\text{cis}$- and $\text{trans}$-dimethoxyethylene (III and IV)] and disubstituted [(acac)Rh(olefin)₂, olefin = $\text{cis}$- and $\text{trans}$-dimethoxyethylene (V and VI), methyl vinyl ether (VII)] derivatives of I have been investigated with respect to hindered intramolecular movements of the ligands. The barriers of olefin rotation increase with an increasing number of methoxy substituents. When the olefin rotation is frozen out; the methoxy substituents of the olefins tend to be turned away from the acetylacetonate ligand unless steric interaction occurs between the two π-coordinated olefins. A hindered movement of the acetylacetonate ligand has been observed in II and V. For this movement which is independent of the olefin rotation, a degenerate rearrangement is proposed of the tetragonal-planar complexes via a tetrahedral transition state.     

Molecular modeling of the olefin metathesis by tungsten(0) carbene complexes

Density functional and second-order Moller–Plesset theory were used to model W(0) carbene mediated homogeneous metathesis reaction of propylene. The calculations show that the rate determining step of the metathesis is the initiation. After the initiation has been completed the rate determining step becomes dissociation of olefin–metallocarbene complex. The low stereoselectivity of the olefin metathesis reaction is due to the close matching of activation energies for cis and trans isomer formation and the fast cis–trans isomerization caused by the catalysts. The non-productive olefin metathesis reaction always dominates the reaction mixture owing to its very low activation energy. The electronic structure of metal carbene olefin complexes can be described as a combination of donor–acceptor interactions between HOMO of the olefin and LUMO of metal carbene located at carbene carbon on the one hand, and the Dewar, Chatt and Duncanson back donation scheme on the other.     

FeCl3‐Catalyzed Ring‐Closing Carbonyl–Olefin Metathesis

Exploiting catalytic carbonyl–olefin metathesis is an ongoing challenge in organic synthesis. Reported herein is an FeCl₃‐catalyzed ring‐closing carbonyl–olefin metathesis. The protocol allows access to a range of carbo‐/heterocyclic alkenes with good efficiency and excellent trans diastereoselectivity. The methodology presents one of the rare examples of catalytic ring‐closing carbonyl–olefin metathesis. This process is proposed to take place by FeCl₃‐catalyzed oxetane formation followed by retro‐ring‐opening to deliver metathesis products.     

Transition metal promoted reactions of unsaturated hydrocarbons : II. Insertion of bicyclic olefins into allylic-palladium and -platinum bonds

Addition of strained olefins, based on norbornene, norbornadiene,benzonorbornadiene or bicyclo [2.2.2] octene skeletons to π-allylic(hexafluoroacetylacetonato) palladium(II) complexes [(π-All)Pd(Hfacac)], gives “enyl” products derived from “insertion” of the olefin into the least substituted terminal allylicpalladium bond. The reaction involves an initial rapid and reversible formation of (gs-allyl)(π-olefin)Pd(Hfacac). The rate-determining step involves migration of a σ-allylic carbon atom from Pd to the coordinated olefin in a concerted cis—exo addition of PdC across the double bond. Remote electronegative substituents on the olefin do not affect the coordinative ability of the olefin towards Pd. They do however inhibit the migration of the σ-allylic ligand to the coordinated olefin. This observation is interpreted in terms of a small degree of polarization of the π-olefin—Pd bond in the transition state for the σ-allyl migration.