Gas-phase reactions of Sc+, Y+, and lanthanide metal ions (M(+)) with 1,3,5-tri-tert-butylbenzene (L) have been investigated at 10(-6) to 10(-7) Torr by means of FT/ICR mass spectrometry in the first systematic study in which all of the lanthanide series elements (except for Pm+) are included. For Sm+, Eu+, Tm+, and Yb+, sandwich complex ions, ML(2)(+), are formed by successive addition of intact ligand. The other metal ions activate C-H and C-C bonds, reacting with the tert-butyl group to form product ions with elimination of hydrogen, methane, and other neutrals. For all of the lanthanide series ions, the primary ion-molecule reaction pathway is controlled by the metal ion electronic configuration and the 4f to 5d promotion energy of the ion.