Reaction of rare earth metal–alkyl complexes [Ln(CH2SiMe3)3(THF)2] (Ln = Y, Lu) with B(C6X5)3 (X = H, F) in the presence of crown ethers gives crystallographically characterized ion pairs [Ln(CH2SiMe3)2(CE)(THF)n]+[B(CH2SiMe3)(C6X5)3]– (CE = [12]-crown-4, n = 1; CE = [15]-crown-5 and [18]-crown-6, n = 0).
