Spectroscopic Capture and Reactivity of a Low-Spin Gobalt(IV)-Oxo Complex Stabilized by Binding Redox-inactive Metal Ions

摘要

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 Sx~(3+), Ce~(3+), Y~(3+), and Zn~(2+), and the investigation of their reactivity in Oil 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 f(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.