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Reactivities and Electronic Structures of μ-1,2-Peroxo and μ-1,2-Superoxo CoIIICoIII Complexes: Electrophilic Reactivity and O2 Release Induced by Oxidation

MPG-Autoren
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Bill,  Eckhard
Research Department DeBeer, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Zitation

Depenbrock, F., Limpke, T., Bill, E., SantaLucia, D. J., van Gastel, M., Walleck, S., et al. (2023). Reactivities and Electronic Structures of μ-1,2-Peroxo and μ-1,2-Superoxo CoIIICoIII Complexes: Electrophilic Reactivity and O2 Release Induced by Oxidation. INORGANIC CHEMISTRY, 62(43), 17913-17930. doi:10.1021/acs.inorgchem.3c02782.


Zitierlink: https://hdl.handle.net/21.11116/0000-000D-FCC6-8
Zusammenfassung
Peroxo complexes are key intermediates in water oxidation catalysis (WOC). Cobalt plays an important role in WOC, either as oxides CoOx or as {Co-III(mu-1,2-peroxo)Co-III} complexes, which are the oldest peroxo complexes known. The oxidation of {Co-III(mu-1,2-peroxo)Co-III} complexes had usually been described to form {Co-III(mu-1,2-superoxo)Co-III} complexes; however, recently the formation of {Co-IV(mu-1,2-peroxo)Co-III} species were suggested. Using a bis(tetradentate) dinucleating ligand, we present here the synthesis and characterization of {Co-III(mu-1,2-peroxo)(mu-OH)Co-III} and {Co-III(mu-OH)(2)Co-III} complexes. Oxidation of {Co-III(mu-1,2-peroxo)(mu-OH)Co-III} at -40 degrees C in CH3CN provides the stable {Co-III(mu-1,2-superoxo)(mu-OH)Co-III} species and activates electrophilic reactivity. Moreover, {Co-III(mu-1,2-peroxo)(mu-OH)Co-III} catalyzes water oxidation, not molecularly but rather via CoOx films. While {Co-III(mu-1,2-peroxo)(mu-OH)Co-III} can be reversibly deprotonated with DBU at -40 degrees C in CH3CN, {Co-III(mu-1,2-superoxo)(mu-OH)Co-III} undergoes irreversible conversions upon reaction with bases to a new intermediate that is also the decay product of {Co-III(mu-1,2-superoxo)(mu-OH)Co-III} in aqueous solution at pH > 2. Based on a combination of experimental methods, the new intermediate is proposed to have a {Co-II(mu-OH)Co-III} core formed by the release of O-2 from {Co-III(mu-1,2-superoxo)(mu-OH)Co-III} confirmed by a 100% yield of O-2 upon photocatalytic oxidation of {Co-III(mu-1,2-peroxo)(mu-OH)Co-III}. This release of O-2 by oxidation of a peroxo intermediate corresponds to the last step in molecular WOC.