Metal ion binding by laterally non-symmetric macrobicyclic oxa–aza cryptands
Macrobicyclic cryptands incorporating amine groups along with oxygen donors that are laterally non-symmetric constitute an important class of organic compounds. These molecules can form inclusion complexes with different transition and main group metal ions. It is also possible to modify the binding characteristics of these compounds through attachment of different groups. Some of these metal complexes can be useful homogeneous catalysts in different organic transformations. If there are chiral centers present in the cryptands, they can be useful in asymmetric syntheses. The three secondary amine groups present in the bridges can be partially or completely derivatized with different fluorophores for fluorescence signaling of transition, inner-transition and heavy metal ions. It is also possible to sequentially attach different fluorophores to study single- as well as multi-step Förster resonance energy transfer. Different donor/acceptor groups can be attached to study second and third order optical nonlinearity. The present article describes several aspects of the chemistry of laterally non-symmetric cryptands and provides future directions for research in this area.