Heme and nonheme high-valent manganese(V)-oxo complexes: Synthesis, characterization, and reactivity

High-valent metal-oxo species have been proposed, and in certain instances confirmed, as the key intermediates in enzymatic and biomimetic oxidation reactions. Further, high-valent Mn-oxo species are considered as the active intermediates responsible for water oxidation in Photosystem II and catalytic water oxidation reactions by synthetic metal catalysts. Identification of these intermediates is crucial for understanding the fundamental principles of enzymatic and biomimetic reactions. However, the active intermediates in oxidation reactions, especially the high-valent metal-oxo species, have short lifetimes and are highly reactive in nature, causing significant challenges for capturing and characterizing in mechanistic studies. Therefore, synthetic high-valent metal-oxo complexes have garnered significant interest among chemists. In this review, we provide a systematic overview of the synthesis and structural and spectroscopic characterization of both heme and nonheme Mn^V-oxo complexes, along with their reactivities in hydrogen-atom transfer (HAT), oxygen-atom transfer (OAT), electron-transfer (ET), and O−O bond formation reactions. Emphasis is also placed on the influence of the ligands, the presence of axial ligands, the kinds of solvents, and the use of Lewis or Brønsted acids on the electronic structures, chemical properties, reactivities, and reaction mechanisms of the heme and nonheme Mn^V-oxo complexes.