Binding of molecular oxygen and alkenes to coordinatively unsaturated bipyridinium metal complexes in the gas phase

Unsaturated metal complexes have vacant sites for binding and may promote insertion reactions. Rate coefficients were determined for the formation of adduct ions in ion-molecule reactions between M(bipy)22+ (M = Cr, Ru, or Os; bipy = bipyridine) and dioxygen, propane, ethene, propene, and 1-butene in the cell of a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Together with estimated capture rate coefficients, these lead to efficiencies for adduct formation. Efficiencies for O2 adduct formation are small, which is indicative of a weak binding between the metal and dioxygen. The efficiency was independent of pressure, and consequently radiative emission must be responsible for cooling of the excited adducts, M(bipy)2(O2)2+*. The efficiency for addition of alkenes to Ru(bipy)22+ is higher. Reactions between Ru(bipy)2(alkene)2+ and alkene were investigated. In the case of ethene, simple addition occurred to give the Ru(bipy)2(ethene)22+ ion. In contrast, reactions with propene and 1-butene produced the ions Ru(bipy)2(C2H3)(alkene)2+ and Ru(bipy)2(C3H5)(alkene)2+ which are indicative of alkene activation. In the ion-molecule reaction between Ru(bipy)22+ and propene, a small abundance of the bis(allyl) complex, Ru(bipy)(allyl)22+, was also observed. The assignment of the products and elucidation of the detailed reaction mechanisms is based on collisional activation and supported by experiments with deuterium-labeled propene.