GAS-PHASE REACTIVITY OF COORDINATIVELY UNSATURATED TRANSITION METAL COMPLEX IONS TOWARD MOLECULAR OXYGEN

Electrospray mass spectrometry is used to investigate the reactivity of the coordinatively unsaturated ions [M(bipy)2]2+ (M = Cr, Ru, Os) and [M(bipy)]+ (M = Co, Ni) toward O2 to give the dioxygen adducts [M(bipy)2O2]2+ (M = Cr, Ru, Os) and [M(bipy)O2]+ (M = Co, Ni). CID experiments with the [M(bipy)2O2]2+ and [M(bipy)O2]+ adducts show that the loss of a mass equivalent to two oxygen atoms is the predominant process for [M(bipy)2O2]2+ (M = Cr, Ru) and [M(bipy)O2]+ (M = Ni, Co). In contrast, weak signals assigned to [Os(bipy)O2]+, [Os(bipy)O2]2+, and bipy+• indicate loss of a bipyridine ligand from [Os(bipy)2O2]2+ rather than O2 loss. This result may have structural implications and a dioxo Os(VI) complex cation, [Os(bipy)2(O)2]2+, is proposed for the Os−dioxygen adduct. This assignment is consistent with the known solution and solid-state chemistry of osmium. Formation of [OsVI(bipy)2(O)2]2+ involves a formal oxidation of the Os(II) to an Os(VI) and concomitant O2 four-electron reduction of O2. Even thoug...