Autocatalytic Intermolecular versus Intramolecular Deprotonation in C[BOND]H Bond Activation of Functionalized Arenes by Ruthenium(II) or Palladium(II) Complexes

Authors

  • Indira Fabre,

    1. Ecole Normale Supérieure, Département de Chimie, UMR CNRS-ENS-UPMC 8640, 24 rue Lhomond, 75231 Paris Cedex 5 (France)
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  • Niklas von Wolff,

    1. Ecole Normale Supérieure, Département de Chimie, UMR CNRS-ENS-UPMC 8640, 24 rue Lhomond, 75231 Paris Cedex 5 (France)
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  • Dr. Gaëtan Le Duc,

    1. Ecole Normale Supérieure, Département de Chimie, UMR CNRS-ENS-UPMC 8640, 24 rue Lhomond, 75231 Paris Cedex 5 (France)
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  • Dr. Emmanuel Ferrer Flegeau,

    1. Ecole Normale Supérieure, Département de Chimie, UMR CNRS-ENS-UPMC 8640, 24 rue Lhomond, 75231 Paris Cedex 5 (France)
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  • Dr. Christian Bruneau,

    1. Institut Sciences Chimiques, UMR6226 CNRS-Université de Rennes, Campus Beaulieu, Université de Rennes, 35042 Rennes (France)
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  • Prof. Pierre H. Dixneuf,

    1. Institut Sciences Chimiques, UMR6226 CNRS-Université de Rennes, Campus Beaulieu, Université de Rennes, 35042 Rennes (France)
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  • Dr. Anny Jutand

    Corresponding author
    1. Ecole Normale Supérieure, Département de Chimie, UMR CNRS-ENS-UPMC 8640, 24 rue Lhomond, 75231 Paris Cedex 5 (France)
    • Ecole Normale Supérieure, Département de Chimie, UMR CNRS-ENS-UPMC 8640, 24 rue Lhomond, 75231 Paris Cedex 5 (France)

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Abstract

The activation of the C[BOND]H bond of 1-phenylpyrazole (2) and 2-phenyl-2-oxazoline (3) by [Ru(OAc)2(p-cymene)] is an autocatalytic process catalyzed by the co-product HOAc. The reactions are indeed faster in the presence of acetic acid and water but slower in the presence of a base K2CO3. A reactivity order is established in the absence of additives: 2-phenylpyridine>2-phenyl-2-oxazoline>1-phenylpyrazole (at RT). The accelerating effect of added acetate ions reveals an intermolecular deprotonation after C[BOND]H bond activation by a cationic RuII center (SE3 mechanism). The reactions of 1-phenylpyrazole and 2-phenyl-2-oxazoline first lead to the neutral cyclometalated complexes A2 and A3 ligated by one acetate. The latter dissociate to the cationic complexes B2+ and B3+, respectively, and acetate. A slow incorporation of one or two D atoms into 2, 3, and 2-phenylpyridine (1) was observed in the presence of deuterated acetic acid. The “reversibility” of the C[BOND]H bond activation/deprotonation takes place from the cationic complexes Bn+ (n=1–3). They are also involved in oxidative additions to PhI, which are rate-determining and lead to the mono- and bis-phenylated products at high temperatures. A general mechanism is proposed for the arylation of arenes 1–3 catalyzed by [Ru(OAc)2(p-cymene)]. In contrast, the reaction of Pd(OAc)2 with 2-phenylpyridine (1), is much faster: Pd(OAc)2>[Ru(OAc)2(p-cymene)]. Since the kinetics is not affected by added acetates, the reaction proceeds through a CMD mechanism assisted by a ligated acetate (intramolecular process) and is irreversible. A bis-cyclometalated PdII^PdII dimer D′1 is formed whose bielectronic electrochemical oxidation leads to a [PdIII^PdIII]2+ dimer, in agreement with the result of a reported chemical oxidation used in arene functionalizations catalyzed by Pd(OAc)2.

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