Spectroscopic Capture and Reactivity of a Low‐Spin Cobalt(IV)‐Oxo Complex Stabilized by Binding Redox‐Inactive Metal Ions

High-valent cobalt-oxo intermediates are proposed as reactive intermediates in a number of cobalt-complex-mediated oxidation reactions. Herein we report the spectroscopic capture of low-spin (S=1/2) Co(IV)-oxo species in the presence of redox-inactive metal ions, such as Sc(3+), Ce(3+), Y(3+), and Zn(2+), and the investigation of their reactivity in C-H bond activation and sulfoxidation reactions. Theoretical calculations predict that the binding of Lewis acidic metal ions to the cobalt-oxo core increases the electrophilicity of the oxygen atom, resulting in the redox tautomerism of a highly unstable (TAML)Co(III)(O˙)(2-) species to a more stable (TAML)Co(IV)(O)(M(n+)) core. The present report supports the proposed role of the redox-inactive metal ions in facilitating the formation of high-valent metal-oxo cores as a necessary step for oxygen evolution in chemistry and biology.