R?ntgenstrukturanalyse als unentbehrliches Hilfsmittel bei der absoluten Konfigurationszuordnung einiger Iridoidglucoside sowie daraus synthetisierter 12-epi-Prostaglandine

Ohne Zusammenfassung

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X-ray-structure-analysis as indispensable tool in structure elucidation of some iridoidglucosides as well as 12-epi-prostaglandines derived from them

Abkürzungen C(OH)₄ -d-Glucopyranosyl - Ac CH₃—CO - Ts p-CH₃—C₆H₄—SO₂ - Cin C₆H₅—CH=CH—CO - HCin C₆H₅—CH₂—CH₂—CO—O - DME Dimethoxyethan     

Studies on interaction of isocyanide with transition metal complexes : XI. Photochemical reactions of isocyanide complexes of iron

The photochemical reaction of π-C₅H₅Fe(CO)(CNC₆H₁₁)COCH₃ (I) gave the heterocyclic compound π-C₅H₅Fe(CO)[(C=NC₆H₁₁)₂(CH₃)] (II) involving N-coordination to the iron atom. The analogous complex is obtained by the photo-induced reaction of π-C₅H₅Fe(CO)₂CH₃ with C₆H₁₁NC. A similar reaction of π-C₅H₅Fe(CO)[CNC(CH₃)₃]CH₃ with C₆H₁₁NC gave π-C₅H₅Fe(CO)[(C=NC₆H₁₁) {C=N(CH₃)₃}(CH₃)] (IV) involving different N-substituted imino groups. The possible pathways leading to formation of II are discussed. The mass spectra of these complexes were also investigated.     

Oberflächenverbindungen von Übergangsmetallen. XXX. Fischer-Tropsch-analoge Umsetzung von CO/H2 bzw. CO2/H2 an Oberflächen-Chrom(II)

Surface Compounds of Transition Metals. XXX. Fischer-Tropsch Analogous Reactions of CO/H₂ and CO₂/H₂ on Surface Chromium(II) Surface chromium(II)/silicagel catalyzes the reduction of CO and CO₂ by hydrogen to CH₄, C₂H₆ and C₃H₈. The catalyst is partially desactivated by this reaction, but a permanent activity of ca. 30% remains. – The reaction can be formulated via the sequence formaldehyde complex → <CH₂>-complex → alkane. If cycloalkenes or chlorobenzene are added simultaneously, these scavenger molecules are methylated by <CH₂>.     

Mechanism of the radiolytic transformation of cellulose

The formation under -irradiation of volatile products in cellulose preparations with different degrees of crystallinity has been studied. The volatile products of the radiolysis of cellulose have been found to contain H₂, CH₄, H₂O, CO, and C0₂. According to the results obtained, these products can be divided into two groups, the first of which (H₂, H₂O, and CO) is formed as the result of the splitting out of hydrogen atoms and of —OH and —CH₂OH groups from the macromolecule, while the second (CH₄ and CO₂) is the result of radiation-chemical reactions between the components of the volatile products of the first group.Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 921–927, November-December, 1996. Original article submitted February 26, 1996.     

Kinetics of hydrolysis of amino acid esters in the presence of aquocomplexes involving ethylenediamine,diethylenetriamine and triethylenetetramine ligands. Part 2. Cobalt(II), cobalt(III), platinum(II) and palladium(II)

Summary Aquocomplexes of cobalt(II), cobalt(III), palladium(II) and platinum(II) involving (H₂NCH₂)₂, [H₂N(CH₂)₂]₂NH and [H₂N(CH₂)₂NHCH₂]₂ as ligands were prepared and characterized. The kinetics of base hydrolysis of the amino acid esters H₂NCH₂CO₂Me·HCl, HOC₆H₄CH₂CH (NH₂)CO₂Me·HCl, MeS(CH₂)₂CH(NH₂)CO₂Me·HCl, HSCH₂CH(NH₂)CO₂Et·HCl, C₃H₃N₂CH₂CH(NH₂)-CO₂Me·2HCl and [—SCH₂CH(NH₂)CO₂Me]₂·2HCl in the presence of these complexes have been studied. The rate of hydrolysis is influenced substantially by these complexes and the second order rate constants are some 10–90 times greater than those obtained in the presence of simple metal ions.     

Temperature-programmed desorption/pulse surface reaction (tpd/tpsr) studies of CH4, C2H6, C2H4, and CO over a cobalt/MWNTs catalyst

Summary Temperature-programmed desorption (TPD) of CH₄, C₂H₆, C₂H₄, and CO and temperature-programmed pulse surface reactions (TPSR) of CH₄, C₂H₆, C₂H₄, CO, and CO/H₂ over a Co/MWNTs catalyst have been investigated. The TPD results indicated that CH₄ and C₂H₆ mainly exist as physisorbed species on the Co/MWNTs catalyst surface, whilst C₂H₄ and CO exist as both physisorbed and chemisorbed species. The TPSR results indicated that CH₄ and C₂H₆ do not undergo reaction between room temperature and 450^oC. Pulsed C₂H₄ can be transformed into CH₄ at 400 ^oC whilst pulsed CO can be transformed into CO₂ at 100 or 150^oC. In gaseous mixtures of CO and H₂ containing excess CO, the products of pulsed reaction were CH₃CHO and CH₃OH. When the ratio of CO and H₂ was 1:2, pulsed CO and H₂ were transformed into CH₃CHO, CH₃OH and CH₄. In H₂ gas flow, pulsed CO was transformed into a mixture of CH₃CHO and CH₄ between 200 and 250^oC and was transformed into CH₄ only above 250^oC.     

Kinetics of hydrolysis of amino acid esters in presence of aquocomplexes involving ethylenediamine,diethylenetriamine and triethylenetetramine ligands. Part 1-copper(II) and nickel(II)

Summary Aquocomplexes of copper(II) and nickel(II) involving (H₂NCH₂)₂, H₂NCH₂CH₂NHCH₂CH₂NH₂ and H₂NCH₂CH₂NHCH₂CH₂NHCH₂CH₂NH₂ as ligands were prepared and characterised. Using a pH-stat method, the kinetics of the base hydrolysis of amino acid esters such as H₂NCH₂CO₂CH₃·HCl (GE), (HO)C₆H₄CH₂-(NH₂)CO₂CH₃·HCl (TE), CH₃S(CH₂)₂CH(NH₂)CO₂CH₃· HCl (ME), HSCH₂CH(NH₂)CO₂C₂H₅·HCl (CE), (HE) and [—SCH₂CH(NH₂)CO₂CH₃]₂·2HCl (CysE) was studied. These complexes substantially enhance the rate of hydrolysis, the values of the second-order rate constants being some 10–30 times greater than those obtained in the presence of simple metal ions.     

Calcination of SiO2-Aerogel in Inert Atmosphere

Thermal treatment of SiO₂-aerogel in inert atmosphere, in contrary to oxidizing atmosphere, yields a series of gas products with great range of mole masses (12–154 g mol^–1) and every product has specific way of evolving. These substances are represented by CO, CO₂, CH₄, CH₃OH, C₂H₆, C₂H₄ and aromates. Part of evolving products, which are formed during catalytic condensation, is trapped under the surface and after carbonisation it causes opacity of surface layer of aerogel.This revised version was published online in November 2005 with corrections to the Cover Date.     

A Theoretical Investigation of the Decomposition Reactions of Ethyl Formate in the S0 State

This study revisits the stability of the possible conformations and the decomposition reactions of ethyl formate in the S₀ state using the (U)MP2, MP4SDTQ, CCSD(T), and (U)B3LYP methods with various basis sets. The transition states of the decomposition channels to HCOOH + C₂H₄, CO + CH₃CH₂OH, CH₂O + CH₃CHO, HCOH + CH₃CHO, C₂H₆ + CO₂, and H₂ + CH₂CHOCHO are determined. The microcanonical rate constants derived from the RRKM theory are calculated for each of the decomposition reactions. The high‐pressure limit rate constants are calculated for the decomposition channels to HCOOH + C₂H₄, CO + CH₃CH₂OH, and CH₂O + CH₃CHO.     

Thermal dehydration kinetics of disaccharides

The vacuum decomposition of sucrose and cellobiose has been observed in the 150–250°C temperature range. The predominant decomposition product of both sugars is H₂O with less than 5% CO, CO₂, CH₂O, CH₃CHO, CH₃OH, and C₂H₅OH formed. The detailed rates and temperature dependences suggest that with the possible exception of C₂H₅OH, the minor products are formed in secondary reactions of the dehydration products. Further it is shown that the so-called “melting with decomposition” of a sugar is in reality a high-temperature dissolution of the disaccharide in the eliminated water.     

The reaction of carbon monoxide with platinum ylids

The platinum(II) ylids [X₂Pt{CH(py)CH₂CH₃}(py)] (X = Cl, Br; PY = pyridine) react with carbon monoxide to give the platinum carbonyls [CO(X₂)Pt{CH(py)CH₂CH₂CH₃}] which lose CO on heating or in solution. The platinum(IV) ylids [Cl₄Pt{CH(py)CH₂CH₃}(py)] and[Cl₂I(CH₃)Pt{CH(py)CH₂CH₃}(py)] also react with CO to give Pt(CO)-ylid compounds.     

Adsorption of small molecules on helical gold nanorods: A relativistic density functional study

We study the adsorption of a variety of small molecules on helical gold nanorods using relativistic density functional theory. We focus on Au₄₀ which consists of a central linear strand of five gold atoms with seven helical strands of five gold atoms on a coaxial tube. All molecules preferentially adsorb at a single low‐coordinated gold atom on the coaxial tube at an end of Au₄₀. In most cases, there is significant charge transfer (CT) between Au₄₀ and the adsorbate, for CO and NO₂, there is CT from the Au₄₀ to adsorbate while for all other molecules there is CT from the adsorbate to Au₄₀. Thus, Au₄₀‐adsorbate can be described as a donor–accepter complex and we use charge decomposition analysis to better understand the adsorption process. We determine the adsorption energy order to be C₅H₅N >NO₂ > CO > NH₃ > CH₂?CH₂ > CH₂?CH? CHO > NO > HC?CH > H₂S > SO₂ > HCN > CH₃OH > H₂C?O > O₂ > H₂O > CH₄ > N₂. We find that the Au? C, Au? N, Au? S, and Au? O bonds are surprisingly strong, with clear implications for reactivity enhancement of the adsorbate. The Au? H bond is relatively weak but, for interactions via an H atom that is bonded to a carbon atom (e.g., CH₄), we find that there is large charge polarization of the Au? H? C moiety and partial activation of the inert C? H bond. Although the Au? S and Au? O bonds are generally weaker than the Au? C and Au? N bonds, we find that adsorption of H₂S or H₂O causes greater distortion of Au₄₀ in the binding region. However, the degree of distortion is small and the helical structure is retained, demonstrating the stability of the helical Au₄₀ nanorod under perturbations. © 2014 Wiley Periodicals, Inc.     

Reactions of nucleophiles with cyclopentadienyliron complexed halotoluenes

η⁶-o-Chlorotoluene-η⁵-cyclopentadienyliron hexafluorophosphate undergoes nucleophilic substitution of the chlorine atom with anions generated (K₂CO₃/DMF) from methyl thioglycolate, diethyl malonate, dimethyl malonate, methyl acetoacetate and 2,4-pentanedione. The compounds prepared were o-CH₃C₆H₄SCH₂CO₂CH₃FeCp⁺PF₆⁻, o-CH₃C₆H₄CH(CO₂C₂H₅)₂FeCp⁺PF₆⁻, o-CH₃C₆H₄CH(CO₂CH₃)₂FeCp⁺PF₆⁻, o-CH₃C₆H₄CH(COCH₃)CO₂CH₃FeCp⁺PF₆⁻ and o-CH₃C₆H₄CH₂COCH₃FeCp⁺PF₆ . Similarly, the reaction of diethyl malonate, dimethyl malonate, methyl acetoacetate anions and methylamine with η⁶-2,6-dichlorotoluene-η⁵-cyclopentadienyliron hexafluorophosphate yielded monosubstitution of one of the chloro groups. The complexes prepared in this study were η⁶-diethyl(3-chloro-2-methyl) phenylmalonate- η⁵-cyclopentadienyliron hexafluorophosphate, η⁶-dimethyl(3-chloro-2-methyl)phenylmalonate-η⁵-cyclopentadienyliron hexafluorophosphate, η⁶-methyl(3-chloro-2-methyl)phenylacetoacetate-η⁵-cyclopentadienyliron hexafluorophosphate and η⁶-3-chloro(2-methyl-N-methyl)aniline-η⁵-cyclopentadienyliron hexafluorophosphate. Reaction of η⁶-2,6-dichlorotoluene-η⁵-cyclopentadienyliron hexafluorophosphate with excess methanol as well as methyl thioglycolate in the presence of K₂CO₃ resulted in disubstitution of both chloro groups to yield new complexes, η⁶-2,6-dimethoxytoluene-η⁵-cyclopentadienyliron hexafluorophosphate and η⁶-methyl[(2-methylphenyl)1,3-dithio] diacetate-η⁵5-cyclopentadienyliron hexafluorophosphate, respectively. Complexes o-CH₃C₆H₄CH(CO₂C₂H₅)₂FeCp⁺PF₆⁻, o-CH₃C₆H₄CH(CO₂CH₃)₂FeCp⁺PF₆⁻ and o-CH₃C₆H₄CH₂ COCH₃FeCp⁺ PF₆⁻ react with excess K₂CO₃ and benzyl bromide in refluxing methylene chloride to give 80–90% yields of complexes o-CH₃C₆H₄C(CH₂C₆H₅)(CO₂C₂H₅)₂FeCp⁺PF₆⁻, o-CH₃C₆H₄C(CH₂C₆H₅)(CO₂CH₃)₂FeCp⁺PF₆⁻ and o-CH₃C₆H₄CH(CH₂C₆H₅)COCH₃FeCp⁺PF₆⁻, respectively. Reaction of complex, o-CH₃C₆H₄C(CH₂C₆H₅)(CO₂C₂H₅)₂FeCp⁺PF₆⁻ with one molar equivalent of t-BuOK followed by acidic work-up gives o-(C₂H₅CO₂CH₂)C₆H₄CH(CO₂C₂H₅)CH₂C₆H₅FeCp⁺PF₆⁻. Similarly, reactions of complexes o-CH₃C₆H₄C(CH₂C₆H₅)(CO₂C₂H₅)₂FeCp⁺PF₆⁻ and o-CH₃C₆H₄C(CH₂C₆H₅)(CO₂CH₃)₂FeCp⁺PF₆⁻ with t-BuOK in THF followed by alkylation with methyl iodide gave the new complexes, o-(C₂H₅O₂C(CH₃)CH)C₆H₄CH(CH₂C₆H₅)CO₂C₂H₅FeCp⁺PF₆⁻ and o-(CH₃O₂C(CH₃)CH)C₆H₄CH(CH₂C₆H₅)CO₂CH₃FeCp⁺PF₆⁻, respectively. Vacuum sublimation of the new complexes, o-CH₃C₆H₄C(CH₂C₆H₅)(CO₂C₂H₅)₂FeCp⁺PF₆⁻ and o-(C₂H₅O₂CCH₂)C₆H₄CH(CH₂C₆H₅)CO₂C₂H₅FeCp⁺PF₆⁻ gives o-CH₃C₆H₄C(CH₂C₆H₅)(CO₂C₂H₅)₂ and O-(C₂H₅O₂CCH₂)C₆H₄CH(CH₂C₆H₅)CO₂C₂H₅, respectively.     

Gas hydrate equilibrium dissociation conditions in porous media using two thermodynamic approaches

We employ two thermodynamic approaches, based on the equal fugacities and the equal activities, to predict the gas hydrate equilibrium dissociation conditions in the porous media. The predictions are made for the hydrate systems, CH₄/H₂O, C₂H₆/H₂O, C₃H₈/H₂O, CO₂/H₂O, CH₄/CO₂/H₂O, C₃H₈/CH₄/C₂H₆/H₂O, and CH₄/CH₃OH/H₂O. For the non-hydrate phase, we used the Trebble–Bishnoi equation in the fugacity approach and the Soave–Redlich–Kwong equation in the activity approach. For the hydrate phase, the van der Waals–Platteeuw model incorporated with the capillary model of Llamedo et al. [M. Llamedo, R. Anderson, B. Tohidi, Am. Mineral. 89 (2004) 1264–1270] was used in the two approaches. The predictions are found to be in satisfactory to good agreement with the experimental data. The predictive ability of the fugacity approach is better than that of the activity approach.     

Ion cyclotron resonance studies of some reactions of C+ ions

Product distributions and rate constants for the reaction of ground state C⁺ ions with O₂, NO, HCl, CO₂, H₂S, H₂O, HCN, NH₃, CH₄, H₂CO, CH₃OH, and CH₃NH₂ have been measured. Rate constants were obtained using ion cyclotron resonance trapped ion methods at JPL, and product distributions were obtained using a tandem (Dempster-ICR) mass spectrometer at the University of Utah. Rapid carbon isotope exchange has also been observed in C⁺-CO collisions.     

Probing the pyrolysis of ethyl formate in the dilute gas phase by synchrotron radiation and theory

The thermal decomposition of the atmospheric constituent ethyl formate was studied by coupling flash pyrolysis with imaging photoelectron photoion coincidence (iPEPICO) spectroscopy using synchrotron vacuum ultraviolet (VUV) radiation at the Swiss Light Source (SLS). iPEPICO allows photoion mass-selected threshold photoelectron spectra (ms-TPES) to be obtained for pyrolysis products. By threshold photoionization and ion imaging, parent ions of neutral pyrolysis products and dissociative photoionization products could be distinguished, and multiple spectral carriers could be identified in several ms-TPES. The TPES and mass-selected TPES for ethyl formate are reported for the first time and appear to correspond to ionization of the lowest energy conformer having a cis (eclipsed) configuration of the O = C (H)– O – C (H₂)–CH₃ and trans (staggered) configuration of the O= C (H)– O – C (H₂)– C H₃ dihedral angles. We observed the following ethyl formate pyrolysis products: CH₃CH₂OH, CH₃CHO, C₂H₆, C₂H₄, HC(O)OH, CH₂O, CO₂, and CO, with HC(O)OH and C₂H₄ pyrolyzing further, forming CO + H₂O and C₂H₂ + H₂. The reaction paths and energetics leading to these products, together with the products of two homolytic bond cleavage reactions, CH₃CH₂O + CHO and CH₃CH₂ + HC(O)O, were studied computationally at the M06-2X-GD3/aug-cc-pVTZ and SVECV-f12 levels of theory, complemented by further theoretical methods for comparison. The calculated reaction pathways were used to derive Arrhenius parameters for each reaction. The reaction rate constants and branching ratios are discussed in terms of the residence time and newly suggest carbon monoxide as a competitive primary fragmentation product at high temperatures.     

Low-Dimensional Architectures in Isomeric cis-PtCl2{Ph2PCH2N(Ar)CH2PPh2} Complexes Using Regioselective-N(Aryl)-Group Manipulation

The solid-state behaviour of two series of isomeric, phenol-substituted, aminomethylphosphines, as the free ligands and bound to Pt^II, have been extensively studied using single crystal X-ray crystallography. In the first library, isomeric diphosphines of the type Ph₂PCH₂N(Ar)CH₂PPh₂ [1a–e; Ar = C₆H₃(Me)(OH)] and, in the second library, amide-functionalised, isomeric ligands Ph₂PCH₂N{CH₂C(O)NH(Ar)}CH₂PPh₂ [2a–e; Ar = C₆H₃(Me)(OH)], were synthesised by reaction of Ph₂PCH₂OH and the appropriate amine in CH₃OH, and isolated as colourless solids or oils in good yield. The non-methyl, substituted diphosphines Ph₂PCH₂N{CH₂C(O)NH(Ar)}CH₂PPh₂ [2f, Ar = 3-C₆H₄(OH); 2g, Ar = 4-C₆H₄(OH)] and Ph₂PCH₂N(Ar)CH₂PPh₂ [3, Ar = 3-C₆H₄(OH)] were also prepared for comparative purposes. Reactions of 1a–e, 2a–g, or 3 with PtCl₂(η⁴-cod) afforded the corresponding square-planar complexes 4a–e, 5a–g, and 6 in good to high isolated yields. All new compounds were characterised using a range of spectroscopic (¹H, ³¹P{¹H}, FT–IR) and analytical techniques. Single crystal X-ray structures have been determined for 1a, 1b∙CH₃OH, 2f∙CH₃OH, 2g, 3, 4b∙(CH₃)₂SO, 4c∙CHCl₃, 4d∙½Et₂O, 4e∙½CHCl₃∙½CH₃OH, 5a∙½Et₂O, 5b, 5c∙¼H₂O, 5d∙Et₂O, and 6∙(CH₃)₂SO. The free phenolic group in 1b∙CH₃OH, 2f∙CH₃OH_, 2g, 4b∙(CH₃)₂SO, 5a∙½Et₂O, 5c∙¼H₂O, and 6∙(CH₃)₂SO exhibits various intra- or intermolecular O–H∙∙∙X (X = O, N, P, Cl) hydrogen contacts leading to different packing arrangements.     

Rotating ring-disk voltammetry: Diagnosis of catalytic activity of metallic copper catalysts toward CO<Subscript>2</Subscript> electroreduction

Using the rotating ring (platinum)—disk (glassy carbon) electrode methodology, electrocatalytic activity of the microstructured copper centers (imbedded within the polyvinylpyrrolidone polymer matrix and deposited onto the glassy carbon disk electrode) has been monitored during electroreduction of carbon dioxide both in acid (HClO₄) and neutral (KHCO₃) media as well as diagnosed (at Pt ring) with respect to formation of the electroactive products. Combination of the stripping-type and rotating ring-disk voltammetric approaches has led to the observation that, regardless the overlapping reduction phenomena, the reduction of carbon dioxide at copper catalyst is, indeed, operative and coexists with hydrogen evolution reaction. Using the fundamental concepts of surface electrochemistry and analytical voltammetry, the reaction products (thrown onto the platinum ring electrode) could be considered and identified as adsorbates (on Pt) under conditions of the stripping-type oxidation experiment. Judging from the potentials at which the stripping voltammetric peaks appear in neutral CO₂-saturated KHCO₃ (pH 6.8), formic acid or carbon monoxide seem to be the most likely reaction products or intermediates. The proposed methodology also permits correlation between the CO₂ electroreduction products and the potentials applied to the disk electrode. By performing the comparative stripping-type voltammetric experiments in acid medium (HClO₄ at pH 1) with the adsorbates of formic acid, ethanol and acetaldehyde (on Pt ring), it can be rationalized that, although C₂H₅OH or CH₃CHO are very likely CO₂-reduction electroactive products, formation of some HCOOH, CH₃OH or even CO cannot be excluded.     

Synthesis and reactions of the transition metal substituted tin hydride HSn[Mo(CO)3C5H5]3

Reaction of HMo(CO)₃C₅H₅ and Sn(C₅H₅)₂ produces the tin hydride HSn[Mo(CO)₃C₅H₅]₃ (I). Reaction of I with CCl₄, CHCl₃, or CH₂Cl₂ gives ClSn[Mo(CO)₃C₅H₅]₃ (II). With hydrogen chloride the hydride I reacts to produce the dichloride Cl₂Sn[Mo(CO)₃C₅H₅]₂. The first step in this reaction is cleavage of the SnH bond to produce the chloride II. The hydride I reacts with acetic acid to produce the diacetate (CH₃COO)₂Sn[Mo(CO)₃C₅H₅]₂.