CO Oxidation Catalyzed by the Neutral Cluster IrAl₂O₈ with Iridium in a High Oxidation State of VI

Metals with high oxidation states (HOSs) (e.g., +V to +X) are of great interest to chemists, although it is challenging to trigger the reactivity of metals with HOSs, because they are usually highly coordinated to block the approach of reactants. Herein, benefiting from the study of a neutral iridium-aluminum oxide cluster IrAl₂O₈ that can catalytically oxidize four CO molecules, the reactivity of iridium with nearly a +VI oxidation state was identified. In heteronuclear metal oxide clusters, the exposed metal sites with oxidation states lower than +III have been commonly observed to capture reactants for subsequent reactions. However, the embedded Ir^VI+ site in the IrAl₂O₈ cluster is 4-fold coordinated by oxygen atoms, and the direct interaction between Ir^VI+ and CO is weak. The unique reactivity of Ir^VI+ toward CO oxidation has been emphasized. The crucial roles of the oxygen atoms coordinated with Ir^VI+ to modify the electronic structure of Ir during CO oxidation were highlighted.