Hydrogen Bond Mediated Dioxygen Activation in a Manganese Guanidine Complex

A high‐spin manganese(II) complex supported by a guanidine‐based DIG 3 tren (tris(N’, N”‐diisopropylguanidinyl‐2‐ethyl)amine) ligand has been synthesized and investigated with respect to its dioxygen reactivity. The ligand framework is so chosen that it incorporates secondary‐sphere N−H donors capable of interacting with oxygen‐derived ligands. Upon exposure to O 2 in acetonitrile (MeCN), the Mn(II) complex undergoes aerobic oxidation to form a mixed‐valent bis‐μ‐oxo Mn(III)Mn(IV) dimer, as evidenced by UV/Vis and EPR spectroscopy displaying the characteristic 16‐line pattern of an S tot = 1/2 species. Low‐temperature studies reveal additional oxygen‐derived intermediates, and reaction with an oxygen‐atom transfer reagent affords a transient Mn(IV)=O species that thermally converges to a related Mn 2 O 2 core. Cyclic voltammetry confirms that higher oxidation states are accessible within this ligand framework, enabling the observed oxygen activation chemistry. These findings demonstrate that secondary‐sphere hydrogen‐bonding interactions facilitate dioxygen activation and enable stabilization of high‐valent manganese‐oxygen species, potentially enabling ligand participation during OO bond cleavage.