Mononuclear ruthenium complexes containing chiral aminooxazolines: Syntheses, X-ray studies and catalytic activity |
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Authors: | Javier A Cabeza Ignacio del Río Robert A Gossage Lorena Martínez-Méndez Daniel Miguel |
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Institution: | a Departamento de Química Orgánica e Inorgánica, Instituto de Química Organometálica “Enrique Moles”, Universidad de Oviedo-CSIC, E-33071 Oviedo, Spain b The David Upton Hill Laboratories of Inorganic Chemistry, 6 University Avenue, Elliott Hall, Department of Chemistry, Acadia University, Wolfville, Nova Scotia, Canada B4P 2R6 c Área de Química Inorgánica, Facultad de Ciencias, Universidad de Valladolid, E-47071 Valladolid, Spain |
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Abstract: | The synthesis and characterisation of three novel mononuclear ruthenium(II) complexes containing one of the following chiral auxiliary ligands: 2-amino-(4R)-phenyl-2-oxazoline (amphox), indanyl-2-amino-(4R,5S)-2-oxazoline (aminox) or indanyl-(2′-anilinyl)-(4R,5S)-2-oxazoline (aninox) is described using Ru2Cl4(η6-p-cym)2] (p-cym = 1-isopropyl-4-methylbenzene) as the Ru starting material. The new complexes have been identified as the neutral derivatives RuCl2(η6-p-cym)(amphox-κ1Nox)] (1), RuCl2(η6-p-cym)(aminox-κ1Nox)] (2) and the salt RuCl(η6-p-cym)(aninox-κ2N,N′)]Cl (3). These materials have been fully characterised (elemental analysis, NMR, IR, conductance, MS, etc.) and, in the case of 2 and 3, structurally elucidated in the solid-state using single crystal X-ray diffraction methods. All three complexes show good catalytic activity (max. conversion >99%, TOF = 424 h−1) but only modest enantio-selectivity (max. ee = 40%) for the transfer hydrogenation reaction of acetophenone with isopropyl alcohol. The complexes were also tested in an asymmetric Diels-Alder reaction involving cyclopentadiene and acrolein (max. conversion >99%, TOF = 42 h−1). In this case, the diastereo-selectivity was good to moderate (max. de = 84%), but the ee values were poor (max. ee = 12%). |
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Keywords: | Oxazoline Ruthenium X-ray structure Arene complex Catalysis Transfer hydrogenation [4+2] Cycloaddition |
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