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  • Mild oxidative C−H functionalization of alkanes and alcohols using a magnetic core-shell Fe3O4@mSiO2@Cu4 nanocatalyst
    J. Mol. Catal. A Chem. (IF 4.397) Pub Date : 2016-06-28
    Marina V. Kirillova, Carla I.M. Santos, Wenyu Wu, Yu Tang, Alexander M. Kirillov

    A new hybrid Fe3O4@mSiO2@Cu4 material was constructed by loading a bio-inspired tetracopper(II) coordination compound [Cu4(μ4-O){N(CH2CH2O)3}4(BOH)4][BF4]2 (Cu4) onto the Fe3O4@mSiO2 core-shell nanoparticles (NPs) composed of a magnetite (Fe3O4) core and mesoporous silica (mSiO2) shell with perpendicularly aligned channels. The obtained Fe3O4@mSiO2@Cu4 magnetic nanoparticles were characterized by transmission electron microscopy (TEM), FT-IR spectroscopy, thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), and field-dependent magnetization. This hybrid material acts as a magnetically recoverable C−H functionalization nanocatalyst, namely for the mild oxidation, by t-butyl hydroperoxide at 50–70 °C in acetonitrile medium, of cycloalkanes (cyclopentane, cyclohexane, cycloheptane, and cyclooctane) to the corresponding alcohols and ketones (with up to ∼15% yields based on cycloalkane; TON 335). A related oxidation process using cyclohexanol as a more reactive substrate leads to the formation of cyclohexanone in up to ∼25% yield (TON 570). The Fe3O4@mSiO2@Cu4 nanocatalyst can be recycled five times without an appreciable loss of activity. The bond-, regio-, and stereoselectivity parameters were investigated in the oxidation of different alkane substrates (n-hexane, n-heptane, n-octane, methylcyclohexane, adamantane, cis- and trans-1,2-demethylcyclohexane), and the obtained results were compared with the homogeneous systems based on the Cu4 catalyst. In particular, the high bond selectivity parameters detected in the oxidation of methylcyclohexane (1°:2°:3° of 1:8:142) and adamantane (2°:3° of 1:21) catalyzed by Fe3O4@mSiO2@Cu4 suggest that the reactions possibly occur in hydrophobic pockets of the nanocatalyst.

    更新日期:2018-02-02
  • The interplay of catalytic and gas-phase stages at oxidative conversion of methane: A review
    J. Mol. Catal. A Chem. (IF 4.397) Pub Date : 2016-08-11
    Vladimir S. Arutyunov, Ludmila N. Strekova

    The effective functionalization of CH bond in methane, the main hydrocarbon component in Earth's crust and the most real source of energy for mankind in the nearest observable future, is undoubtedly can be regarded nowadays as one of the most important scientific and technological tasks. However, the usual practice of considering catalytic and gas-phase processes as independent technological branches seriously restricts the possibilities for a deeper understanding and technological optimization of real processes. The development of more effective technologies to convert methane and other gas-phase hydrocarbons into more valuable and demanded chemicals needs a complex approach based on the combined heterogeneous–homogeneous chemistry of these processes. A number of examples are used to illustrate the interconnection between heterogeneous catalytic and gas-phase processes in oxidative functionalization of methane. A number of potential possibilities for the optimization of the real heterogeneous–homogeneous chemistry of these processes are discussed.

    更新日期:2018-02-02
  • Insights on the CH Bond activation by Transition Metal Complexes from Groups 8–10 Bearing (P-N) Chelates
    J. Mol. Catal. A Chem. (IF 4.397) Pub Date : 2016-08-18
    Vanessa R. Landaeta, Rafael E. Rodríguez-Lugo

    CH bond catalytic activation/functionalization has been matter of great interest, since these transformations could establish new grounds from the synthetic perspective, and could serve to propose alternative and greener methods for the production of organic molecules. In this sense, the development of efficient catalytic systems for CH bond activation becomes of great importance, and understanding the principles that govern such transformations, either stoichiometric or catalytic, is essential. To study such processes from the mechanistic or catalytic point of view requires of the design of ligands and catalysts able of performing CH bond activation. (P,N)-chelates have arisen as alternative ligands to develop new catalytic systems, due to their combination of different donor atoms, and the ability to tune their steric and electronic characteristics and to create potential vacant sites at the metal center due to hemilability. This mini review summarizes the advances from 2005 to 2015 in the field of CH bond activation at transition metal centers from groups 8–10 bearing (P,N)-chelating ligands. Even when the examples of inter- or intramolecular CH bond activation using transition metal complexes with the (P,N) ligands described herein do not engage yet in catalytic applications, their understanding becomes of great importance and sets the basis for future developments in this field.

    更新日期:2018-02-02
  • Activation and selective oxy-functionalization of alkanes with metal complexes: Shilov reaction and some new aspects
    J. Mol. Catal. A Chem. (IF 4.397) Pub Date : 2016-08-22
    Аlbert А. Shteinman

    The quest of selective catalytic reactions for direct conversion of alkanes into valued products remains to be the most important task objective of modern chemistry and metal complex catalysis. Nowadays it is adopted that the formation of metal–alkyl intermediates (MR) is a necessary condition for activation and functionalization of alkanes on metal complexes but the mechanism of subsequent reactions of metal alkyls remain obscure, so that effective catalytic systems of this kind are still rare and uncommon. Although it is widely adopted that alkane σ-complexes (M·RH) most frequently are primary hydrocarbon intermediates in these processes, low profile in the literature is given to their reactivity and these are often considered simply just as some ‘collision complexes’. Nevertheless, theoretical and experimental studies provide more and more evidence that the СН bonds in such complexes may be markedly weakened and/or polarized, thus opening wide horizons for occurrence of subsequent direct homolytic or heterolytic reactions of alkanes. This review addresses the discussion of new routes for activation and oxygenation of saturated hydrocarbons, including those via alkane σ-complexes, without formation of metal–alkyl intermediates.

    更新日期:2018-02-02
  • Cage-like metallasilsesquioxanes in catalysis: A review
    J. Mol. Catal. A Chem. (IF 4.397) Pub Date : 2016-06-23
    Mikhail M. Levitsky, Alexey I. Yalymov, Alena N. Kulakova, Аrtem А. Petrov, Аlexey N. Bilyachenko

    The review describes catalytic properties of a unique class of metal complexes—polycyclic cage-like metallasilsesquioxanes. Article is composed in retrospective manner and reflects the progress of the investigations in the field: from classic applications to recently discovered perspectives of cage-like metallasilsesquioxanes in catalysis of oxidation of С–H compounds.

    更新日期:2018-02-02
  • Metal-catalyzed CH activation/functionalization: The fundamentals
    J. Mol. Catal. A Chem. (IF 4.397) Pub Date : 2016-09-04
    Fares Roudesly, Julie Oble, Giovanni Poli

    An isolated CH bond in a molecule has a very low reactivity owing to the large kinetic barrier associated to the CH bond cleavage and the apolar nature of this bond. For this reason, the selective reactivity of such a non-functional group is under active study since several decades and is still regarded as the Holy Grail in chemistry. Metal-catalyzed CH activation/functionalization chemistry allows the step-economical and original construction of CC as well as CO and CN bonds starting from hydrocarbons (or hydrocarbon fragments) without the need of prior non catalytic oxidation steps. Furthermore, it can be of utmost importance in the domain of multistep syntheses, and also in transformations of societal significance such as the conversion of methane into methanol. This tutorial review addresses to students and researchers who would like to become acquainted with this fascinating topic. After a brief historical introduction, the main mechanistic fundaments of metal-catalyzed CH activation are exposed. Then, a selection of seminal advances and conceptual breakthroughs are presented.

    更新日期:2018-02-02
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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