A Redox‐Active Ligand as a Reservoir for Protons and Electrons: O 2 Reduction at Zirconium(IV)

The [ONO] ligand {(ONO cat ) 3– = bis(3,5‐di‐ tert ‐butyl‐2‐phenoxy)amide} can be installed onto zirconium(IV) in two different protonation states. The reaction of (ONO cat ) 3– with ZrCl 4 afforded the octahedral complex (ONO cat )ZrCl(THF) 2 ( 1 ). This complex, characterized in the solid state by single‐crystal X‐ray diffraction and in solution by NMR,UV/Vis, and IR spectroscopy, is assigned as a zirconium(IV) complex coordinated to the fully reduced form of the [ONO] redox‐active ligand. When (ONO cat )H 3 was doubly deprotonated and treated with ZrCl 4 , the complex (ONHO)ZrCl 2 (THF) ( 2 ) was isolated, in which one ligand proton remains on the [ONO] ligand. Exposure of 2 to dry O 2 resulted in a four‐electron, two‐proton reaction to form the bis(hydroxo) complex [(ONO q )ZrCl 2 (μ‐OH)] 2 ( 3 ), which shows that the [ONO] ligand platform can serve as both an electron and proton reservoir in small‐molecule reactions.