A ruthenium(II) bipyridine complex with proximal phenylselenium tethers, [Ru](H2O)(2), reacted intramolecularly with O-2 in a protic slightly acidic solvent, 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), to yield an O-O bond cleaved product, [Ru](O)(2), with formation of two Ru-O-Se moieties. This stable compound was isolated, and its structure was determined by X-ray diffraction, The identification of the compound in solution was confirmed by ESI-MS and the H-1 NMR with the associated Curie plot that showed that [Ru](O)(2) was paramagnetic. The magnetic susceptibility was 2.8 mu(B) by Evan's method suggesting a ground state triplet or biradical. DFT calculations, however, predicted a ground state singlet and an oxidized Se atom. Further it was shown that [Ru](O)(2) is a potent oxygen transfer species of both O-2-derived atoms to triphenylphosphine and a nucleophilic alkene such as 2,3-dimethyl-2-butene in both HFIP and acetonitrile. UV-vis spectroscopy combined with the measured stoichiometry of PPh3:O-2 = similar to 2 in a catalytic oxidation of PPh3 suggests a dioxygenase type activation of O-2 with structural identification of the O-O bond cleavage reaction step, formation of [Ru](O)(2) as an intermediate, and the proof that [Ru](O)(2) is a donor of both oxygen atoms.