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Activation of Molecular Oxygen by a Cobalt(II) Tetra-NHC Complex** |
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| Authors: | Jonas F. Schlagintweit Dr. Philipp J. Altmann Alexander D. Böth Benjamin J. Hofmann Dr. Christian Jandl Clemens Kaußler Linda Nguyen Dr. Robert M. Reich Dr. Alexander Pöthig Prof. Dr. Fritz E. Kühn |
| Affiliation: | 1. Molecular Catalysis, Catalysis Research Center and Department of Chemistry, Technische Universität München, Lichtenbergstraße 4, 85747 Garching bei München, Germany;2. Molecular Catalysis, Catalysis Research Center and Department of Chemistry, Technische Universität München, Lichtenbergstraße 4, 85747 Garching bei München, Germany Single Crystal XRD Laboratory of the Catalysis Research Center, Technische Universität München, Ernst-Otto-Fischer-Str. 1, 85747 Garching bei München, Germany These authors contributed equally to this work.;3. Single Crystal XRD Laboratory of the Catalysis Research Center, Technische Universität München, Ernst-Otto-Fischer-Str. 1, 85747 Garching bei München, Germany;4. Molecular Catalysis, Catalysis Research Center and Department of Chemistry, Technische Universität München, Lichtenbergstraße 4, 85747 Garching bei München, Germany Ausbildungszentrum der Technischen Universität München, Technische Universität München, Lichtenbergstraße 4, 85747 Garching bei München, Germany |
| Abstract: | The first dicobalt(III) μ2-peroxo N-heterocyclic carbene (NHC) complex is reported. It can be quantitatively generated from a cobalt(II) compound bearing a 16-membered macrocyclic tetra-NHC ligand via facile activation of dioxygen from air at ambient conditions. The reaction proceeds via an end-on superoxo intermediate as demonstrated by EPR studies and DFT. The peroxo moiety can be cleaved upon addition of acetic acid, yielding the corresponding CoIII acetate complex going along with H2O2 formation. In contrast, both CoII and CoIII complexes are also studied as catalysts to utilize air for olefin and alkane oxidation reactions; however, not resulting in product formation. The observations are rationalized by DFT-calculations, suggesting a nucleophilic nature of the dicobalt(III) μ2-peroxo complex. All isolated compounds are characterized by NMR, ESI-MS, elemental analysis, EPR and SC-XRD. |
| Keywords: | cobalt dioxygen activation dioxygen ligands macrocyclic ligands N-heterocyclic carbenes |