Alkali and alkaline earth metal cryptates

This chapter discusses the alkali and alkaline earth metal cryptates. The classical approach to cryptands with bridgehead nitrogen atoms involves the high dilution reaction of a secondary bis-amine coronand with the required bis-acid chloride, followed by reduction of the resultant bisamide with diborane. Such an approach has been used to synthesize, for example, and also the related pyridinophane cryptand. The high dilution technique requires gradual mixing of reagents in order to avoid polymerization reactions, although Dye has shown that the reaction may be effected in under a minute if the reagents are efficiently mixed in a suitable flow cell. The simple approach to diazamacrocyclic ligands is in stark contrast to the rather lengthy and/or low-yielding procedures required to synthesize the cryptands with carbon atoms at the bridgehead.