Gas-Phase Reactions of Doubly Charged Lanthanide Cations with Alkanes and Alkenes. Trends in Metal(2+) Reactivity

The gas-phase reactivity of doubly charged lanthanide cations, Ln(2+) (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), with alkanes (methane, ethane, propane, n-butane) and alkenes (ethene, propene, 1-butene) was studied by Fourier transform ion cyclotron resonance mass spectrometry. The reaction products consisted of different combinations of doubly charged organometallic ions-adducts or species formed via metal ion induced hydrogen, dihydrogen, alkyl, or alkane eliminations from the hydrocarbons-and singly charged ions that resulted from electron, hydride, or methide transfers from the hydrocarbons to the metal ions. The only lanthanide cations capable of activating the hydrocarbons to form doubly charged organometallic ions were La2+, Ce2+, Gd2+, and Tb2+, which have ground-state or low-lying d(1) electronic configurations. Lu2+, with an accessible d(1) electronic configuration but a rather high electron affinity, reacted only through transfer channels. The remaining Ln(2+) reacted via transfer channels or adduct formation. The different accessibilities of d(1) electronic configurations and the range of electron affinities of the Ln(2+) cations allowed for a detailed analysis of the trends for metal(2+) reactivity and the conditions for occurrence of bond activation, adduct formation, and electron, hydride, and methide transfers.