Mn(III)–O–Ce(IV) as a Surrogate for Highly Reactive Non-Heme Mn(IV)═O Species Supported by Benzimidazole-Based Ligand

High Resolution Image Download MS PowerPoint Slide The interaction of high-valent manganese–oxo species with Ca 2+ plays a paramount role in the catalytic water oxidation reaction within the oxygen-evolving complex of photosystem II. In artificial systems, redox-active Lewis acids like Ce 4+ have emerged as promising components when coordinated to metal–oxo complexes. Herein, we report the synthesis, detailed characterization, and reactivity of two novel complexes (L 5 )Mn III –O–Ce IV ( 2B/2M, L 5 = BnTBEN = N 1 -benzyl- N 1, N 2, N 2 -tris((1-methyl-1 H -benzo[ d ]imidazole-2-yl)methyl)ethane-1,2-diamine and MeTBEN = N 1 -methyl- N 1, N 2, N 2 -tris((1-methyl-1 H -benzo[ d ]imidazole-2-yl)methyl)ethane-1,2-diamine) in MeCN at ambient conditions. The incorporation of benzimidazole ligands enhances their reactivity in both oxygen atom transfer and hydrogen atom transfer reactions relative to pyridine analogs. Remarkably, adding HClO 4 or Sc III (OTf) 3 to 2B/2M triggers the formation of highly reactive [(L 5 )Mn IV ═O] 2+ species ( 3B/3M ). These findings are in sharp contrast with our previous report, where the reaction of (BnTPEN)Mn III –O–Ce IV with HClO 4 and Sc III (OTf) 3 resulted in the formation of (BnTPEN)Mn IV –OH and (BnTPEN)Mn IV –O–Sc III, respectively. These newly formed Mn IV ═O intermediates ( 3B/3M ) were extensively characterized by various spectroscopies and ESI-MS. Notably, [(L 5 )Mn IV ═O] 2+ exhibits superior reactivity toward thioanisole derivatives at −40 °C in MeCN, surpassing the known nonheme high-valent Mn IV ═O species reported thus far. This study advances understanding of ligand effects on high-valent manganese–oxo species and highlights their potential in oxidation catalysis.