The importance of the counter-cation in reductive rare-earth metal chemistry: 18-crown-6 instead of 2,2,2-cryptand allows isolation of [Y II (NR ₂ ) ₃ ] ¹⁻ and ynediolate and enediolate complexes from CO reactions

The use of 18-crown-6 (18-c-6) in place of 2.2.2-cryptand (crypt) in rare earth amide reduction reactions involving potassium has proven to be crucial in the synthesis of Ln( ii ) complexes and isolation of their CO reduction products.