Ligand Effects on the Hydrogenation of Biomass-Inspired Substrates with Bifunctional Ru, Ir, and Rh Complexes

Authors

  • Eveline Jansen,

    1. van ‘t Hoff Institute for Molecular Chemistry, University of Amsterdam, Science Park 904, 1098 XH Amsterdam (The Netherlands)
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  • Linda S. Jongbloed,

    1. van ‘t Hoff Institute for Molecular Chemistry, University of Amsterdam, Science Park 904, 1098 XH Amsterdam (The Netherlands)
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  • Dr. Dorette S. Tromp,

    1. van ‘t Hoff Institute for Molecular Chemistry, University of Amsterdam, Science Park 904, 1098 XH Amsterdam (The Netherlands)
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  • Dr. Martin Lutz,

    1. Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht (The Netherlands)
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  • Prof. Dr. Bas de Bruin,

    1. van ‘t Hoff Institute for Molecular Chemistry, University of Amsterdam, Science Park 904, 1098 XH Amsterdam (The Netherlands)
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  • Prof. Dr. Cornelis J. Elsevier

    Corresponding author
    1. van ‘t Hoff Institute for Molecular Chemistry, University of Amsterdam, Science Park 904, 1098 XH Amsterdam (The Netherlands)
    • van ‘t Hoff Institute for Molecular Chemistry, University of Amsterdam, Science Park 904, 1098 XH Amsterdam (The Netherlands)

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Abstract

We herein report on the application and structural investigation of a new set of complexes that contain bidentate N-heterocyclic carbenes (NHCs) and primary amine moieties of the type [M(arene)Cl(L)] [M=Ru, Ir, or Rh; arene=p-cymene or pentamethylcyclopentadienyl; L=1-(2-aminophenyl)-3-(n-alkyl)imidazol-2-ylidine]. These complexes were tested and compared in the hydrogenation of acetophenone with hydrogen. Structural variations in the chelate ring size of the heteroditopic ligand revealed that smaller chelate ring sizes in combination with ring conjugation in the ligand are beneficial for the activity of this type of catalyst, favoring an inner-sphere coordination pathway. Additionally, increasing the steric bulk of the alkyl substituent on the NHC aided the reaction, showing almost no induction period and formation of a more active catalyst for the n-butyl complex relative to complexes with smaller Me and Et substituents. As is common in hydrogenation reactions, the activity of the complexes decreases in the order Ru>Ir>Rh. The application of [Ru(p-cym)Cl(L)]PF6, which outperforms its reported analogues, has been successfully extended to the hydrogenation of more challenging biomass-inspired substrates.

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