Iridium(III) Complexes Bearing Chelating Bis‐NHC Ligands and Their Application in the Catalytic Reduction of Imines

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  • Francisco Aznarez
    Institut für Anorganische und Analytische Chemie Westfälische Wilhelms‐Universität Münster Corrrensstrasse 30 48149 Münster Germany
  • Manuel Iglesias
    Departamento de Química Inorgánica‐ISQCH Universidad de Zaragoza‐CSIC Plaza San Francisco S/N 50009 Zaragoza Spain
  • Alexander Hepp
    Institut für Anorganische und Analytische Chemie Westfälische Wilhelms‐Universität Münster Corrrensstrasse 30 48149 Münster Germany
  • Benjamin Veit
    Institut für Anorganische und Analytische Chemie Westfälische Wilhelms‐Universität Münster Corrrensstrasse 30 48149 Münster Germany
  • Pablo J. Sanz Miguel
    Departamento de Química Inorgánica‐ISQCH Universidad de Zaragoza‐CSIC Plaza San Francisco S/N 50009 Zaragoza Spain
  • Luis A. Oro
    Departamento de Química Inorgánica‐ISQCH Universidad de Zaragoza‐CSIC Plaza San Francisco S/N 50009 Zaragoza Spain
  • Guo‐Xin Jin
    Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials Department of Chemistry Fudan University 220 Handan Road 200433 Shanghai P. R. China
  • F. Ekkehardt Hahn
    Institut für Anorganische und Analytische Chemie Westfälische Wilhelms‐Universität Münster Corrrensstrasse 30 48149 Münster Germany

抄録

<jats:p>The Ir<jats:sup>III</jats:sup> complexes <jats:bold>4</jats:bold> and <jats:bold>5</jats:bold> bearing bis‐NHC ligands (NHC = N‐heterocyclic carbene) composed of one classical NR,NR NHC and one N,NR NHC donor were prepared by the reaction of the azolium/azole compounds <jats:bold>2</jats:bold>I and <jats:bold>3</jats:bold>Br, respectively, with [{Cp*IrCl(µ‐Cl)}<jats:sub>2</jats:sub>] (Cp*=η<jats:sup>5</jats:sup>‐C<jats:sub>5</jats:sub>Me<jats:sub>5</jats:sub>) in the presence of NaOAc as base. Most likely, the salts <jats:bold>2</jats:bold>I and <jats:bold>3</jats:bold>Br were first selectively deprotonated at the C2 position of the disubstituted (NR,NR) diazaheterocycle to generate an NHC donor, which then coordinated to the Ir<jats:sup>III</jats:sup> center. Subsequently, NaOAc promoted C–H bond activation at the pendant imidazole moiety of the intermediate Ir<jats:sup>III</jats:sup> mono‐NHC complexes led to the formation of the six‐membered iridacycles <jats:bold>4</jats:bold> and <jats:bold>5</jats:bold>, which bear a chelating, doubly <jats:italic>C</jats:italic>‐metalated C(NHC)<jats:sup>^</jats:sup>C(NHC′) bis‐NHC ligand. The Ir<jats:sup>III</jats:sup> complexes <jats:bold>4</jats:bold> and <jats:bold>5</jats:bold> were tested as precatalysts for the reduction of imines with molecular hydrogen. Moderate to good activity was observed at a catalyst loading of 5 mol‐% and an H<jats:sub>2</jats:sub> pressure of 3 bar in MeOH.</jats:p>

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