Activation of Molecular Oxygen by a Cobalt(II) Tetra‐NHC Complex

The first dicobalt(III) μ (2)‐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 Co(III) acetate complex going along with H(2)O(2) formation. In contrast, both Co(II) and Co(III) 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) μ (2)‐peroxo complex. All isolated compounds are characterized by NMR, ESI‐MS, elemental analysis, EPR and SC‐XRD.