Endogenous and exogenous ligand-dependent formation of a superoxide-bridged dicobalt(III) complex and mononuclear Co^III complexes with amide-based macrocyclic ligands

We report superoxide-bridged dicobalt(III) complex 1 supported by 13-membered amide-based macrocyclic ligand H₂L^H. Complex 1 displays a sharp radical-type EPR spectrum (g = 2.031) and a short O-O distance (1.303 Å). Complex 1 can be synthesized by the reaction of in situ generated [Co²⁺(L^H)] species with O₂ or KO₂ as well as by the reaction of (Et₄N)[Co³⁺(L^H)(Cl)₂] (2) with KO₂. In contrast, analogous macrocyclic ligands carrying Cl and CH₃ substituents on the aromatic ring produced the mononuclear Co³⁺ complexes [Co(L^Cl)(Cl)(dmf)] (3) and [Co(L^Me)(Cl)(dmf)] (4) under identical reaction conditions. Furthermore, the reaction of H₂L^H with Co(OAc)₂ yielded the mononuclear Co³⁺ complex [Co(L^H)(η²-OAc)] (5) with a unique bidentate acetate group and a highly distorted six-coordinate geometry around the metal. Steric factors induced by the endogenous and exogenous ligands are believed to control the formation of the distinct cobalt complexes.