Gas-phase reactivity of lanthanide cations with fluorocarbons: C-F versus C-H and C-C bond activation

The gas-phase reactivity of the fluorinated hydrocarbons CF4, CHF3, CH3F, C2F6, 1,1-C2H4F2, and C6F6 with the lanthanide cations Ce+, Pr+, Sm+, Ho+, Tm+, and Yb+ and the reactivity of C6H5F with all lanthanide cations Ln+ (Ln = La-Lu, with the exception of Pm+) have been examined by Fourier-transform ion cyclotron resonance mass spectrometry. The perfluorinated compounds tetrafluoromethane and hexafluoroethane as well as trifluoromethane do not react with any lanthanide cation. Selective activation of the strong C-F bonds in fluoromethane, 1,1-difluoroethane, hexafluorobenzene, and fluorobenzene appears as a general reaction scheme along the 4f row. Experimental evidence is given for a 'harpoon'-like mechanism for the F atom abstraction process which operates via an initial electron transfer from the lanthanide cation to the fluorinated substrate in the encounter complex Ln+RF. The most reactive lanthanides La+, Ce+, Gd+, and Tb+ and also the formal closed-shell species Lu+ exhibit additional C-H and C-C bond activation pathways in the reaction with fluorobenzene, namely dehydrohalogenation as well as loss of a neutral acetylene molecule. In the case of Tm+ and Yb+ the formation of neutral LnF3 is observed in a multistep process via C-C coupling and charge transfer. 17 refs., 2 figs., 2 tabs