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Resorcinarene-Functionalised Imidazolium Salts as Ligand Precursors for Palladium-Catalysed Suzuki–Miyaura Cross-Couplings

Authors

  • Dr. Neslihan Şahin,

    1. Université de Strasbourg, Laboratoire de Chimie Inorganique Moléculaire et Catalyse, UMR 7177 CNRS, 1 rue Blaise Pascal, 67008 Strasbourg Cedex (France)
    2. Department of Chemistry, Faculty of Science, Cumhuriyet University, Sivas, TR 58140 (Turkey)
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  • Dr. David Sémeril,

    Corresponding author
    1. Université de Strasbourg, Laboratoire de Chimie Inorganique Moléculaire et Catalyse, UMR 7177 CNRS, 1 rue Blaise Pascal, 67008 Strasbourg Cedex (France)
    • Université de Strasbourg, Laboratoire de Chimie Inorganique Moléculaire et Catalyse, UMR 7177 CNRS, 1 rue Blaise Pascal, 67008 Strasbourg Cedex (France)
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  • Dr. Eric Brenner,

    Corresponding author
    1. Université de Strasbourg, Laboratoire de Chimie Inorganique Moléculaire et Catalyse, UMR 7177 CNRS, 1 rue Blaise Pascal, 67008 Strasbourg Cedex (France)
    • Université de Strasbourg, Laboratoire de Chimie Inorganique Moléculaire et Catalyse, UMR 7177 CNRS, 1 rue Blaise Pascal, 67008 Strasbourg Cedex (France)
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  • Dr. Dominique Matt,

    Corresponding author
    1. Université de Strasbourg, Laboratoire de Chimie Inorganique Moléculaire et Catalyse, UMR 7177 CNRS, 1 rue Blaise Pascal, 67008 Strasbourg Cedex (France)
    • Université de Strasbourg, Laboratoire de Chimie Inorganique Moléculaire et Catalyse, UMR 7177 CNRS, 1 rue Blaise Pascal, 67008 Strasbourg Cedex (France)
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  • Prof. İsmail Özdemir,

    1. Department of Chemistry, Faculty of Science and Art, Inönü University, Malatya, TR 44280 (Turkey)
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  • Prof. Cemal Kaya,

    1. Department of Chemistry, Faculty of Science, Cumhuriyet University, Sivas, TR 58140 (Turkey)
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  • Loïc Toupet

    1. Institut de Physique, UMR 6251 CNRS, Université de Rennes 1, Campus de Beaulieu, 35042-Rennes Cedex (France)
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Abstract

Three imidazolium salts based on a rigid resorcinarene platform (13) were synthesised and used as catalyst precursors in the Suzuki–Miyaura cross-coupling of aryl halides with phenylboronic acid. In these pro-carbene ligands, the heterocyclic moiety has one N atom connected to a C2 atom of a resorcinolic ring, and the other is substituted by an alkyl group (R=n-propyl, iso-propyl, benzyl). The methinic C atoms of the macrocyclic core are all substituted by a pentyl group. The best catalytic performances were obtained by using an imidazolium/Pd ratio of 1:1. The catalytic systems displayed high activities, which increased in the order R=n-propyl (1)<i-propyl (2)<benzyl (3). For example, the use of 3 resulted in activities up to 30 100 mol(converted ArX) mol(Pd)−1 h−1 in the arylation of bromotoluene at 100 °C in dioxane. Comparative studies showed that the performance of imidazolium salt 3 is significantly superior to that of related salts devoid of a cavity-shaped substituent. These experiments illustrate the role of the bulky resorcinarene unit, which facilitates the reductive elimination step. Modification of the cavitand structure by replacement of the pentyl substituents with phenyl groups further revealed that the catalytic outcome is influenced by the nature of the lower belt-substituents. The results strongly suggest that the Pd catalysts obtained from 13 have the metal centre preferentially located outside the cavity.

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