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

• Published in: Angewandte Chemie (International ed.) 2014-09, Vol.53 (39), p.10403-10407
• Main Authors: Hong, Seungwoo, Pfaff, Florian F., Kwon, Eunji, Wang, Yong, Seo, Mi-Sook, Bill, Eckhard, Ray, Kallol, Nam, Wonwoo
• Format: Article
• Language: English
• Subjects: Binding; Biological evolution; Biology; Bonding; cobalt; Cobalt - chemistry; Coordination Complexes - chemistry; Formations; Ions - chemistry; Lewis acids; Mathematical analysis; Metal ions; Metals - chemistry; Oxidation-Reduction; oxo ligands; Oxygen - chemistry; Oxygen atoms; oxygenation; Quantum Theory; redox tautomerization; Spectroscopy
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201405874

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) CoIV‐oxo species in the presence of redox‐inactive metal ions, such as Sc3+, Ce3+, Y3+, and Zn2+, 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)CoIII(O.)]2− species to a more stable [(TAML)CoIV(O)(Mn+)] 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. What is the metal's role? Cobalt(IV)‐oxo complexes binding redox‐inactive metal ions, such as Sc3+, Ce3+, Y3+, and Zn2+, are investigated in oxygenation reactions. Theory predicts that the binding of metal ions to the cobalt‐oxo core increases the electrophilicity of the oxygen atom. This result supports the role of 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. CAN=cerium ammonium nitrate.