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

The interaction of high-valent manganese-oxo species with Ca²⁺ 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 Ce⁴⁺ have emerged as promising components when coordinated to metal-oxo complexes. Herein, we report the synthesis, detailed characterization, and reactivity of two novel complexes (L₅)Mn^III-O-Ce^IV (2B/2M, L₅ = BnTBEN = N¹-benzyl-N¹,N²,N²-tris((1-methyl-1H-benzo[d]imidazole-2-yl)methyl)ethane-1,2-diamine and MeTBEN = N¹-methyl-N¹,N²,N²-tris((1-methyl-1H-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 HClO₄ or Sc^III(OTf)₃ to 2B/2M triggers the formation of highly reactive [(L₅)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 HClO₄ 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, [(L₅)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.