Terminal high-valent metal oxo species have long been identified as key intermediates involved in the operation of the ubiquitous Cytochrome P450 and Photosystem II metalloenzyme families. Over the past decades, a plethora of synthetic analogs of these systems have been developed, some of them demonstrating impressive efficiency in C-H bond activation and oxygen atom transfer (OAT) reactions. Perhaps the most studied metal-oxo compounds are those of iron -exhibiting catalytic abilities unrivaled by other metaloxos. In contrast, high-valent manganese-oxo systems are less explored, primarily due to their poor stability and complicated reactivity, often significantly deviating from the established 'rebound' mechanism, which dominates the Fe-oxo chemistry. Of the several oxidation states reported for terminal Mn-oxo complexes (III, IV, and V), Mn(IV)-oxo is by far the most elusive, making its study beyond spectroscopic techniques and computational methods highly challenging. To better understand the structure-function relationship of this important intermediate, a significant body of work on such systems was carried out, first by Suslick with the "picketfence" porphyrins (complex I, Figure ), and later by Fukuzumi and Nam , along with various other poly-pyridyl ligands first reported by the same authors and later modified and extensively studied by Jackson and others (complexes II and III, Fig. ).