N,N,O Pincer Ligand with a Deprotonatable Site That Promotes Redox‐Leveling, High Mn Oxidation States, and a Mn 2 O 2 Dimer Competent for Catalytic Oxygen Evolution

The new complex [Mn(bipyalk)(H 2 O)(µ‐O)] 2 (OTf) 2 {bipyalk = 2‐([2,2′‐bipyridin]‐6‐yl)propan‐2‐olate} catalyzes oxygen evolution with a TOF of 0.0055 s –1 when driven by the sacrificial oxidant KHSO 5 in water. It is proposed on the basis of EPR experiments that the catalyst proceeds through a Mn V (µ‐O) 2 Mn V =O intermediate supported by the highly donating tertiary alkoxide moiety of the ligand. The Mn(IV,IV) dimer can also be formed electrochemically from its precursor, Mn(bipyalkH)Cl 2 . A related series of bis‐ligated monomers of the type [Mn n (bipyalkH x )(bipyalkH y )](PF 6 ) 2 is also reported, where the dication features Mn II , Mn III , and Mn IV oxidation states and corresponding protonation states. Electrochemical data on this series underscore the importance of proton loss at the alcohol/alkoxide moiety during oxidation to maintain low overpotentials required for catalysis.