The oxo wall revisited: Cobalt oxo vs. cobalt oxyl

Terminal oxo complexes of late transition metals are frequently proposed reactive intermediates. However, they are scarcely known beyond Groupá8. Using mass spectrometry, we prepared and characterized two such complexes: [(N4Py)Co^III(O)]⁺ (1) and [(N4Py)Co^IV(O)]²⁺ (2). Infrared photodissociation spectroscopy revealed that the CoáO bond in 1 is rather strong, in accordance with its lack of chemical reactivity. On the contrary, 2 has a very weak CoáO bond characterized by a stretching frequency of á659ácm^á1. Accordingly, 2 can abstract hydrogen atoms from nonáactivated secondary alkanes. Previously, this reactivity has only been observed in the gas phase for small, coordinatively unsaturated metal complexes. Multireference abáinitio calculations suggest that 2, formally a cobalt(IV)áoxo complex, is best described as cobalt(III)áoxyl. Our results provide important data on changes to metaláoxo bonding behind the oxo wall and show that cobaltáoxo complexes are promising targets for developing highly active CáH oxidation catalysts. It was published recently in Angewandte Chemie-International Edition.

E. Andris, R. Navrátil, J. Jaáík, M. Srnec, M. Rodríguez, M. Costas, and J. Roithová
“MáO Bonding Beyond the Oxo Wall: Spectroscopy and Reactivity of Cobalt(III)-Oxyl and Cobalt(III)-Oxo Complexes”
Angew. Chem. Int. Ed. 2019, 58, 9619-9624 [abstract]
DOI: 10.1002/anie.201904546