A series of mononuclear Co(II) complexes with noninnocent (redox-active) ligands are prepared that exhibit metal− ligand cooperativity during the reversible binding of O 2 . The complexes have the general formula, [Co II (L S,N )(Tp R2 )] (R = Me, Ph), where L S,N is a bidentate o-aminothiophenolate and Tp R2 is a hydrotris(pyrazol-1-yl)borate scorpionate with R-substituents at the 3and 5-positions. Exposure to O 2 at room temperature results in oneelectron oxidation and deprotonation of L S,N . The oxidized derivatives possess substantial "singlet diradical" character arising from antiferromagnetic coupling between an iminothiosemiquinonate (ITSQ •− ) ligand radical and a low-spin Co(II) ion. The [Co II (Tp Me2 )-( X2 ITSQ)] complexes, where X = H or tBu, coordinate O 2 reversibly at reduced temperatures to provide Co/O 2 adducts. The O 2 binding reactions closely resemble those previously reported by our group (Kumar et al., J. Am. Chem. Soc. 2019,141, 10984−10987) for the related complexes [Co II (Tp Me2 )( tBu2 SQ)] and [Co II (Tp Me2 )( tBu2 ISQ)], where tBu2 (I)SQ represents 4,6-di-tert-butyl-(2-imino)semiquinonate radicals. In each case, the oxygenation reaction proceeds via the addition of O 2 to both the cobalt ion and the ligand radical, generating metallocyclic cobalt(III)-alkylperoxo structures. Thermodynamic measurements elucidate the relationship between O 2 affinity and redox potentials of the (imino)(thio)semiquinonate radicals, as well as energetic differences between these reactions and conventional metal-based oxygenations. The results highlight the utility and versatility of noninnocent ligands in the design of O 2 -absorbing compounds.