Reaction of a redox-active ligand complex of nickel with dioxygen probes ligand-radical character.

Bis(imino)pyridine complex [Ni{2,6-(ArN=CMe)(2)C(5)H(3)N}Cl] (where Ar = 2,6-(i)Pr(2)C(6)H(3)) was synthesized by reduction of the corresponding dichloride complex and characterized as a ligand-radical complex of Ni(II). Reaction of this complex with O(2) caused intraligand C-C bond cleavage to afford the Ni complex of the new iminoethylpyridylcarboxamidato ligand, which also was isolated as the corresponding carboxamide, 6-(ArN=CMe)C(5)H(3)N-2-C(O)NHAr. This reaction serves as an example of small-molecule activation effected directly at the redox-active bis(imino)pyridine ligand without an overall oxidation state change at the Ni center.