Definitive Proof for the Operation of Isotopically Sensitive Branching (‘Metabolic Switching’) in FeI-Mediated C?H Bond Activation in the Gas Phase Short Communication

Rigorous regio- and stereospecific labeling experiments are performed to demonstrate the operation of the previously suggested operation of ‘isotopically sensitive branching’ in Fe^I-mediated C? H bond activation. For the hexane-1,6-diol/Fe⁺-complex, it is shown that dehydrogenation involves specifically the central C(3)/C(4) position, and the study of the stereospecifically labeled D ,L - and meso-[3,4-D₂]-isotompomers 1e and 1f demonstrates that dehydrogenation proceedes via two competing pathways (i.e. ‘anti’- vs. ‘syn’-route). The contribution of these routes to the product formation is – due to a kinetic isotope effect – controlled by the relative configuration at the labeled positions C(3)/C(4). For the D ,L -form 1e , we estimate a ratio of 49:1 in favor of the ‘anti’-route; due to an isotope effect, this ratio drops to 4.3:1 for the meso-form 1f .     

Substituent Effects on Fe+-Mediated [4+2] Cycloadditions in the Gas Phase

The Fe⁺-mediated [4+2] cycloaddition of dienes with alkynes has been examined by four-sector ion-beam and ion cyclotron resonance mass spectrometry. Prospects and limitations of this reaction were evaluated by investigating several Me-substituted ligands. Me Substitution at C(2) and C(3) of the diene, i.e., 2-methylbuta-1,3-diene, 2,3-dimethylbuta-1,3-diene, hardly disturbs the cycloaddition. Similarly, variation of the alkyne by use of propyne and but-2-yne does not affect the [4+2] cycloaddition step, but allows for H/D exchange processes prior to cyclization. In contrast, Me substituents in the terminal positions of the diene moiety (e.g., penta-1,3-diene, liexa-2,4-diene) induce side reactions, namely double-bond migration followed by [3+2] and [5+2] cycloadditions, up to almost complete suppression of the [4+2] cycloaddition for 2,4-dimethylhexa-2,4-diene. Similarly, alkynes with larger alkyl substituents (pent-1-yne, 3,3-dimethylbut-1-yne) suppress the [4 + 2] cycloaddition route. Stereochemical effects have been observed for the (E)- and (Z)-penta-1,3-diene ligands as well as for (E,E)- and (E,Z)-hexa-2,4-diene. A mechanistic explanation for the different behavior of the stereoisomers in the cyclization reaction is developed. Further, the regiochemical aspects operative in the systems ethoxyacetylene/pentadiene/Fe⁺ and ethoxyacetylcne/isoprene/Fe⁺ indicate that substituents avoid proximity.     

Regioselectivity and Stereoselectivity in the Intramolecular Nitrile Oxide-Olefin Cycloaddition (INOC) Reaction and the Intramolecular Silyl Nitronate-Olefin Cycloaddition (ISOC) Reaction

Both INOC and ISOC reactions of 1 which has two different double bonds in a molecule (allylic and homoallylic double bond) showed high regioselectivity for allylic double bond to make [5,5] ring system. INOC reactions of 1 and 6 showed high diastereoselectivity for 4-substituents, whereas ISOC reaction did for 6-substituents of tetrahydrofuroisoxazolines.     

A convenient preparation of (1R,2S,7S,8R)-3,5-diaza-2,7-dimethyl-1,8-diphenyloctan-1,8-diol and its enantiomer

The synthesis of (1R,2S,7S,8R)-3,5-diaza-2,7-dimethyl-1,8-diphenyloctan-1,8-diol 6 and its enantiomer 7 are described utilising (-)-(1R,2S)- or (+)-(1S,2R)-norephedrine, respectively.     

气相中La催化乙烯脱氢及C-C键耦合的理论研究

采用密度泛函理论中的B3LYP方法研究了气相中过渡金属La在二、四重态势能面上催化C2H4的反应机理。全参数优化了二、四重态势能面上各个驻点的几何构型,同时对过渡态进行了频率分析,使用内禀反应坐标（IRC）方法验证了过渡态的准确性,通过AIM理论和NBO分析方法对主要的驻点进行了键分析,并对2IM1、2IM3进行了态密度分析。结果表明：La与C2H4的反应存在两种可能的路径,反应在二重态势能面上进行且均为放热反应。键分析表明初始复合物中La与C2H4分子之间为共价作用。     

Heterogeneously Catalysed Oxidative Dehydrogenation of Menthol in a Fixed-Bed Reactor in the Gas Phase

For the first time, the oxidative dehydrogenation of (−)-menthol to (−)-menthone and (+)-isomenthone in a marketable quality was carried out in a continuous gas phase reactor as a sustainable process using molecular oxygen as green oxidant and solid catalysts which do not contaminate the product mixture and which are easily to remove. The diastereomeric purity remained largely unchanged. Three types of catalysts were found to be very active and selective in the formation of menthone and isomenthone: AgSr/SiO₂, CuO distributed on a basic support and RuMnCe/CeO₂, where Ru, Mn and Ce exist in an oxidized state. The best overall yield of menthon/isomenthone obtained with an Ag-based catalyst was 58 % at 64 % selectivity, with a Cu-based catalyst 41 % at 51 % selectivity and with a Ru-based catalyst 68 % at 73 % selectivity. Reaction conditions were widely optimized.     

Cu(I) and Fe(II) complexes with N,N-dimethylthioformamide and Fe(II) complexes with N,N-dimethylformamide

The synthesis of the following Cu(I) and Fe(II) complexes with N,N-dimethylthioformamide (DMTF) and N,N-dimethylformamide (DMF) are described: Cu(DMTF)₄ClO₄, Cu(DMTF)₂Cl, Cu(DMTF)₂Br, Cu(DMTF)₂I, Fe(DMTF)₆(ClO₄)₂, Fe(DMTF)₂Cl₂, Fe(DMTF)₂Br₂, Fe(DMTF)₂I₂, Fe(DMF)₆(ClO₄)₂, Fe(DMF)₂Cl₂, Fe(DMF)Br₂ and Fe(DMF)₃I₂. Electronic absorption spectra, IR spectra, magnetic susceptibilities of the solids and in solution as well as conductivities have been measured of these compounds in order to obtain information on the nature of the interaction between the cations and the ligands, the coordination in the crystalline state, in solution and the dissociation of these compounds in the respective solvents.     

Tautomerism and Regioselectivity of the Protonation of 2-Pyrrolidone. Stereoselectivity of Complexation between Palladium(II), Chloride Ion,and 2-Pyrrolidone

According to the AM1, PM3, HF/6-31G(d,p), and MP2/6-31G(d,p)//HF/6-31G(d,p) calculations, it is the lactam tautomer of 2-pyrrolidone that is thermodynamically most stable in both the gas phase and an aqueous solution. Analysis of the PM3 data with consideration of the medium showed that the tautomeric equilibrium of 2-pyrrolidone (pyrroline-2-ol) in aqueous solution is shifted to the lactim form, which thus can be involved in complexation with palladium(II). 2-Pyrrolidone was found to be protonated at the O atom in both the gas phase and aqueous solution, in agreement with the concept of the mesomeric displacement of the electron density in the amide fragment. The aqueous medium stabilizes the lactim tautomer of 2-pyrrolidone more strongly than the lactam tautomer and the O-protonated cyclic amide than the N-protonated one. The stereoselectivity of complexation between palladium(II), chloride ion, and pyrroline-2-ol was explained. The initially formed tetragonal-pyramidal adduct with an axial organic ligand undergoes rearrangement into an intermediate with an extra axial Cl atom, which is a precursor of the cis-product. The thermodynamically less stable cis-isomer of the complex [PdCl₂(pyrrolin-2-ol)₂] is formed from the thermodynamically most favorable intermediate in associative nucleophilic substitution. At the supramolecular level, the cis-product can be stabilized by intermolecular dipole-dipole association in the crystal.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 7, 2005, pp. 523–529.Original Russian Text Copyright © 2005 by Pankratov, Borodulin, Chaplygina.     

Stereoselectivity and chiral recognition in copper(I) olefin complexes with a chiral diamine

Trigonal copper(I) complexes of the chiral bidentate ligand (1S,2S)-N,N'-Bis-(mesitylmethyl)-1,2-diphenyl-1,2-ethanediamine ((S,S)-1) have been prepared with hydrocarbon olefins, as well as with allylic alcohols and ethers. The stereochemistry of the complexes has been investigated by 1H NMR spectroscopy and by combined quantum mechanics and molecular mechanics (QM/MM) computational methods. The coordinated chiral nitrogen atoms can display equal (R, R) or opposite (R, S) configuration, the latter being disfavored if steric hindrance is present above and below the coordination plane. Although the complexes exist as rapidly equilibrated mixtures of stereoisomers, one of these is often dominant, and prochiral olefins are coordinated with high enantioface selection. In addition, the [(S,S)-1]-Cu+ fragment selectively recognizes the R enantiomer of secondary allylic alcohols and ethers, as confirmed by the X-ray crystal structure analysis of the adduct with (R)-1-buten-3-ol. The reasons for the observed selectivities have been elucidated, and lead to some implications which are consistent with the enantioselection observed in catalytic cyclopropanation reactions promoted by copper complexes of the same ligand.     

Hydration of Sugars in the Gas Phase: Regioselectivity and Conformational Choice in N‐Acetyl Glucosamine and Glucose

The influence of an acetamido group in directing the preferred choice of hydration sites in glucosamine and a consequent extension of the working rules governing regioselective hydration and conformational choice, have been revealed through comparisons between the conformations and structures of “free” and multiply hydrated phenyl N‐acetyl‐β‐D ‐glucosamine (βpGlcNAc) and phenyl β‐D ‐glucopyranoside (βpGlc), isolated in the gas phase at low temperatures. The structures have been assigned through infrared ion depletion spectroscopy conducted in a supersonic jet expansion, coupled with computational methods. The acetamido motif provides a hydration focus that overwhelms the directing role of the hydroxymethyl group; in multiply hydrated βpGlcNAc the water molecules are all located around the acetamido motif, on the “axial” faces of the pyranose ring rather than around its edge, despite the equatorial disposition of all the hydrophilic groups in the ring. The striking and unprecedented role of the C‐2 acetamido group in controlling hydration structures may, in part, explain the differing and widespread roles of GlcNAc, and perhaps GalNAc, in nature.     

非贵金属(Mn,Co,Fe)配合物催化醇类脱氢偶联/缩合反应研究进展

随着全球资源的可持续利用以及绿色化学的发展,近年来,利用非贵金属配合物催化反应取得了重要进展,我们主要概述非贵金属催化的以醇作为偶联试剂的脱氢反应的最新成果,重点介绍锰,钴,铁配合物的成功应用.     

Kinetic Isotope Effects and exo/endo-Face Selectivity in the Unimolecular Dehydrogenation of Norborneol Alkoxides in the Gas Phase

The study of specifically labeled alkoxides generated in the gas phase by deprotonation of epimeric norbernols demonstrates, beyond any doubt, that ‘solvated’ hydride ions are formed as intermediates in the course of enolate formation. Kinetic isotope effects and exo/endo-face selectivities for the dehydrogenation are discussed.     

New Insights into the Mechanism and an Expanded Scope of the Fe(III)-Mediated Vinblastine Coupling Reaction

A definition of the scope of aromatic substrates that participate with catharanthine in an Fe(III)-mediated coupling reaction, an examination of the key structural features of catharanthine required for participation in the reaction, and the development of a generalized indole functionalization reaction that bears little structural relationship to catharanthine itself are detailed. In addition to providing insights into the mechanism of the Fe(III)-mediated coupling reaction of catharanthine with vindoline suggesting the reaction conducted in acidic aqueous buffer may be radical mediated, the studies provide new opportunities for the preparation of previously inaccessible vinblastine analogs and define powerful new methodology for the synthesis of indole-containing natural and unnatural products.     

Internal Mobility, Phase Transition, and Ionic Conductivity in Thallium(I) Heptafluorodiantimonate(III)

The internal mobility of fluorine ions and the electrophysical properties of TlSb₂F₇ were studied by the ¹⁹F NMR method and impedance spectroscopy. Modes of ionic motions in the fluoride subsystem were determined in the temperature range 213–430 K. A structural phase transition is found to occur at 400 K, resulting in the TlSb₂F₇ modification characterized by high ionic (superionic) conductivity in the temperature range of 400–430 K 2.5·10^-3 S/cm at 430 K).     

Selective detection of Fe(III) ions in aqueous solution with a 1,8-diacridylnaphthalene-derived fluorosensor

The syn-isomer of 1,8-bis(4,4′-diisopropyl-9,9′-diacridyl)naphthalene, 1, has been prepared by two consecutive Pd(PPh₃)₄-catalyzed Stille cross-coupling steps. This highly congested sensor undergoes Fe(III)-selective fluorescence quenching in water/acetonitrile even in the presence of excess of other metal ions.