Treatment of [(Me₃tpa)Ir^II(ethene)]²⁺ (Me₃tpa = N,N,N-tri(6-methyl-2-pyridylmethyl)amine) (1²⁺) with dioxygen in weakly coordinating solvents results in formation of [(Me₃tpa)Ir^III(ethene)(superoxo)]²⁺ (4a²⁺). In the presence of DMPO (DMPO = 5,5-dimethyl-2-pyrrolidine-1-oxide) DMPO is substituted for ethene, and subsequently oxidized to DMPOX by the superoxo fragment to give [(Me₃tpa)Ir^III(DMPOX)]²⁺ (7²⁺; DMPOX = 5,5-dimethyl-2-pyrrolidone-1-oxide). In acetonitrile, in the absence of DMPO, oxygenation of 1²⁺ to [(Me₃tpa)Ir^III(formylmethyl)(MeCN)]²⁺ (2²⁺) is observed. In the presence of DMPO the formation of 2²⁺ and 7²⁺ is competing. Oxygenation of 1²⁺ to 2²⁺ may proceed via4a²⁺, involving an insertion mechanism at the metal. However, a mechanism based on olefin ligand non-innocence seems a reasonable alternative. This involves formation of acetonitrile adduct [(Me₃tpa)Ir(ethene)(MeCN)]²⁺ (3²⁺), which has a significant metalla-ethyl radical (Ir^III–CH₂CH₂˙) character, allowing attack of ³O₂directly at the ethene ligand. Both pathways are discussed on the basis of experimental observations and DFT geometry optimizations.