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On the Importance of Decarbonylation as a Side-Reaction in the Ruthenium-Catalysed Dehydrogenation of Alcohols: A Combined Experimental and Density Functional Study

Authors

  • Dr. Nicolas Sieffert,

    Corresponding author
    1. Département de Chimie Moléculaire, UMR-5250, ICMG FR-2607 CNRS, Université Joseph Fourier Grenoble I, 301 rue de la Chimie, BP 53, 38041 Grenoble Cedex 9 (France)
    • Nicolas Sieffert, Département de Chimie Moléculaire, UMR-5250, ICMG FR-2607 CNRS, Université Joseph Fourier Grenoble I, 301 rue de la Chimie, BP 53, 38041 Grenoble Cedex 9 (France)

      Michael Bühl, EaStCHEM School of Chemistry, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9ST (UK)

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  • Romain Réocreux,

    1. Laboratoire de Chimie, Ecole Normale Superieure de Lyon, 46 Allee d'Italie, 69364 Lyon Cedex 07 (France)
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  • Patrizia Lorusso,

    1. EaStCHEM School of Chemistry, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9ST (UK)
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  • Prof. Dr. David J. Cole-Hamilton,

    1. EaStCHEM School of Chemistry, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9ST (UK)
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  • Prof. Dr. Michael Bühl

    Corresponding author
    1. EaStCHEM School of Chemistry, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9ST (UK)
    • Nicolas Sieffert, Département de Chimie Moléculaire, UMR-5250, ICMG FR-2607 CNRS, Université Joseph Fourier Grenoble I, 301 rue de la Chimie, BP 53, 38041 Grenoble Cedex 9 (France)

      Michael Bühl, EaStCHEM School of Chemistry, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9ST (UK)

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Abstract

We report a density functional study (B97-D2 level) of the mechanism(s) operating in the alcohol decarbonylation that occurs as an important side-reaction during dehydrogenation catalysed by [RuH2(H2)(PPh3)3]. By using MeOH as the substrate, three distinct pathways have been fully characterised involving either neutral tris- or bis-phosphines or anionic bis-phosphine complexes after deprotonation. α-Agostic formaldehyde and formyl complexes are key intermediates, and the computed rate-limiting barriers are similar between the various decarbonylation and dehydrogenation paths. The key steps have also been studied for reactions involving EtOH and iPrOH as substrates, rationalising the known resistance of the latter towards decarbonylation. Kinetic isotope effects (KIEs) were predicted computationally for all pathways and studied experimentally for one specific decarbonylation path designed to start from [RuH(OCH3)(PPh3)3]. From the good agreement between computed and experimental KIEs (observed kH/kD=4), the rate-limiting step for methanol decarbonylation has been ascribed to the formation of the first agostic intermediate from a transient formaldehyde complex.

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