Neutral and cationic trimethylsilylmethyl complexes of the rare earth metals supported by a crown ether: synthesis and structural characterization

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.