The synthesis of a series of thermally robust, isolable trimethylsilylmethyl complexes of the rare earth metals stabilized by 12-crown-4 [Ln(CH₂SiMe₃)₃(12-crown-4)] (Ln = Sc, Y, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) is reported. The crystallographically characterized yttrium and lutetium complexes [Ln(CH₂SiMe₃)₃(12-crown-4)] exhibit facial coordination of the crown ether at the neutral lanthanide trialkyl unit. The coordination geometry can be derived from a capped octahedron. VT NMR spectroscopic studies revealed a labile coordination of the crown ether in thf solution. Reaction of the diamagnetic derivatives with triethylammonium tetraphenylborate in thf results in the clean formation of the cationic dialkyl complexes [Ln(CH₂SiMe₃)₂(12-crown-4)(thf)_y][BPh₄] (Ln = Sc, Y, y = 0; Ln = Lu, y = 1), which also exhibit an exocyclic coordination of the crown ether to the cationic dialkyl lanthanide fragment.