2.2.2-Cryptand

[2.2.2]Cryptand is the organic compound with the formula N(CH₂CH₂OCH₂CH₂OCH₂CH₂)₃N. This bicyclic molecule is the most studied member of the cryptand family of chelating agents. It is a white solid. Many analogous compounds are known. Their high affinity for alkali metal cations illustrates the advantages of "preorganization", a concept within the area of supramolecular chemistry.

For the design and synthesis of [2.2.2]cryptand, Jean-Marie Lehn shared the Nobel Prize in Chemistry. The compound was originally prepared starting with the diacylation of the diamine-diether:

[CH₂OCH₂CH₂NH₂]₂ + [CH₂OCH₂COCl]₂ → [CH₂OCH₂CH₂NHC(O)CH₂]₂ + 2 HCl

The resulting macrocyclic diamide is reduced by lithium aluminium hydride. The resulting macrocyclic diamine tetraether reacts with a second equivalent of [CH₂OCH₂COCl]₂ to produce the macrobicyclic diamide. This di(tertiary)amide is reduced to the diamine by diborane.

[2.2.2]Cryptand binds K⁺ as an octadentate N₂O₆ ligand. The resulting cation K([2.2.2]cryptand)⁺ is lipophilic.

File:Cryptate of potassium cation.jpg

Structure of [2.2.2]cryptand encapsulating a potassium cation (purple) as determined by X-ray crystallography