Activation of Molecular Oxygen by a Dioxygenase Pathway by a Ruthenium Bis-bipyridine Compound with a Proximal Selenium Site

A ruthenium(II) bipyridine complex with proximal phenylselenium tethers, [Ru](H2O)2, reacted intramolecularly with O2 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 1H NMR with the associated Curie plot that showed that [Ru](O)2 was paramagnetic. The magnetic susceptibility was 2.8 μB 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 O2-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:O2 = ∼2 in a catalytic oxidation of PPh3 suggests a dioxygenase type activation of O2 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.