Although terminal Co^IV-O, Ni^III-O and Cu^III-O intermediates have been implicated as active intermediates in a number of important chemical transformations, no spectroscopic evidences for the species are available, leaving the pathway uncertain. Evidences of the presence of terminal M-O units (M = Cu(III), Ni(III) or Co(IV)) are to date limited to mass spectrometric studies in the gas phase. Theory suggests that they should be powerful oxidants, perhaps even more reactive than the related [Fe^IV=O]²⁺ units that have been extensively studied. In this presentation, we will summarize some of our recent efforts to stabilize the elusive metal-oxo and isoelectronic metal-imido units of Cu(III), Co(IV) and Ni(III) ) in solution phase at low temperatures. The high-valent metal-oxo or metal-imido assignments are made on the basis of a variety of spectroscopic methods. The reactivity of the intermediates in hydrogen atom abstraction, oxo transfer reactions and dioxygen reduction reactions are also discussed.