The organolanthanide complexes Ln{C(SiHMe₂)₃}₃ (Ln = La, 1a; Ce, 1b; Pr, 1c; Nd, 1d) react with one or two equiv. of B(C₆F₅)₃ to yield the well-defined zwitterionic species Ln{C(SiHMe₂)₃}₂HB(C₆F₅)₃ (Ln = La, 2a; Ce, 2b; Pr, 2c; Nd, 2d) or LnC(SiHMe₂)₃{HB(C₆F₅)₃}₂ (Ln = La, 3a; Ce, 3b; Pr, 3c; Nd, 3d), respectively. These complexes are shown to contain labile, bridging Si–H⇀Ln and o-F->Ln interactions based upon the observation of low one-bond silicon-hydrogen coupling constants (¹J_SiH) in ¹H NMR spectra of 2a and 3a, the presence of one set of C₆F₅ signals in the ¹⁹F NMR spectra of 2a and 3a, the detection of only m-F and p-F resonances in ¹⁹F NMR spectra of 2b-d and 3b-d, two ν_SiH bands in IR spectra of 2a-d, and X-ray crystallography analyses of 2b and 3d. In addition, a hexametertoluene molecule is coordinated to neodymium in 3d. Reactions of 1a and (AlMe₃)₂ yield labile adducts with an approximate stoichiometry of 1a·3AlMe₃. Exchange between free and bound AlMe₃ groups was observed in EXSY NMR experiments with greater than 3 equiv. of AlMe₃. Compounds 2a-d and 3a-d, in the presence of AliBu₃, are precatalysts for polymerization of butadiene. The neodymium alkyl 3d has the highest activity of the series, and its performance is consistent with chain transfer reactions with AliBu₃.