Catalytic oxidations of organic compounds with atom-efficient, inexpensive, and readily available oxygen sources are widely recognized as the most economical and ecological routes to produce valuable oxygenated products and intermediates for organic synthesis. [[1], [2], [3], [4], [5]] In Nature, the ubiquitous monooxygenase cytochrome P-450 enzymes (P450s) contain an iron porphyrin core and catalyze a wide range of oxidation reactions with remarkable reactivity and selectivity. [[6], [7], [8]] Over decades, significant scientific efforts have been directed to synthesize various metal complexes, such as metalloporphyrins and metallocorroles, to function as biomimetic models and catalysts for diverse catalytic transformations. [[9], [10], [11], [12], [13], [14], [15]] Among these bioinspired catalysts, metal phthalocyanines (MPcs) also stand out in view of their structural similarity to heme-containing macrocycles and their ease of large-scale synthesis, making MPcs highly accessible. [16,17] Notably, MPcs feature rich redox chemistry along with desirable optical absorption and emission properties, leading to a range of applications in catalysis, organic electronics and optics, sensors, and industrial pigments. [[18], [19], [20], [21]] Additionally, MPcs are also easily modified to achieve enhanced steric and electronic control, offering advantages in comparison to related porphyrin counterparts. As a result, MPcs have been extensively employed as redox catalysts, [[22], [23], [24]] including in large-scale industrial processes such as the Merox process, which involves Co(II)Pc complexes for the catalytic aerobic oxidation of mercaptans to remove sulfur from petroleum products. [25] More recently, MPcs have been shown to catalyze a high chemo-, site-, and regioselective allylic C − H amination of olefins. [[26], [27], [28]]

In both biological and chemical oxidation processes, high-valent transition metal-oxo intermediates exhibit a wide range of reactivities and play crucial roles in serving as active species responsible for oxygen atom transfer (OAT). [[29], [30], [31], [32]] However, their high reactivity and low concentrations at which they are formed present many challenges for detailed studies. [33] In this regard, extensive research has focused on metalloporphyrins as P450 enzyme models, leading to the production and characterization of various active metal-oxo species to elucidate heme-mediated oxidation mechanisms. [[34], [35], [36], [37], [38], [39], [40]] In contrast, the mechanistic understanding of MPc-catalyzed oxidations lags behind that of their metalloporphyrin counterparts, primarily due to the limited studies on Pc-metal-oxo intermediates and their reactivities. [21] In 2012, Sorokin and colleagues reported the first high-valent iron(IV)-oxo radical cation species on a phthalocyanine framework. [41] The formation of a diiron(IV)–oxo species was also indicated in μ-nitrido bis-phthalocyanines. [42] More recently, we utilized a photochemical approach to generate a reactive manganese(IV)-oxo phthalocyanine [43], providing further insight into the versatility and reactivity of metal-oxo species within the phthalocyanine platform. These findings suggest that the mechanistic features of MPc-mediated oxidations may parallel those of their porphyrinoid analogs. However, the reactivity and mechanistic understanding of metal-oxo species within phthalocyanine complexes remains largely unexplored. In this paper, we present our comprehensive studies on the reactivity of manganese-oxo phthalocyanines generated by photochemical and chemical methods in two systems (Scheme 1). The kinetic studies conducted with various organic substrates offered valuable insights into the structure-function relationship and oxidation mechanism of these intermediates, enhancing our understanding of their role in catalytic oxidation reactions.