Donor makes the difference: The mononuclear η1‐superoxo copper(II) complex 1 undergoes dioxygen activation with the addition of hydrogen‐atom donors. Net O2‐derived O‐atom insertion into the N‐methyl group of the ligand leads to formation of a copper(II)‐alkoxide product 2. The cupric superoxo species 1 itself is not capable of the observed hydroxylation reaction.

Der Donor macht den Unterschied: Der Disauerstoff‐Ligand des einkernigen η1‐Superoxo‐Kupfer(II)‐Komplexes 1 wird durch Wasserstoffatomdonoren aktiviert. Der resultierende Einschub eines O‐Atoms aus der O2‐Gruppe in die N‐gebundene Methylgruppe des Chelatliganden führt zu dem Kupfer(II)‐alkoxid 2. Ohne Zusatz des Donors ist die Superoxospezies 1 nicht in der Lage, die beobachtete Hydroxylierung einzugehen.

A discrete peroxynitrite-copper(II) complex, [(TMG3tren)CuII(-OONO)]+ (3), has been generated in solution (ESI-MS, m/z = 565.15; tetragonal EPR) by reacting *NO(g) with superoxo complex [(TMG3tren)CuII(O2*-)]+ (2). Complex 3 undergoes a thermal transformation to give CuII-nitrite complex [(TMG3tren)CuII(-ONO)]+ (4) (X-ray) along with ca. 0.5 molar equiv dioxygen. A DFT calculation derived structure with cyclic bidentate k2-O,O'-OONO bound peroxynitrite moiety and dx2-y2 ground state is proposed. Experiments using 18O2 suggest that the adjacent peroxo oxygen atoms in 3 are derived from molecular oxygen. Further, 18O2 containing 3 undergoes O-O bond cleavage to form singly 18-O-labeled 4. The results suggest the viability of biological CuI/O2/(*NO) peroxynitrite formation and chemistry, that is, not coming from free superoxide plus *NO reaction.