Cryptate inclusion complexes, effects on solute-solute and solute-solvent interactions and on ionic reactivity

Cryptation of a suitable metal cation by inclusion into a macrobicyclic ligand leads to a large organic cation presenting much weaker interactions with the environment. As a result solute-solute and solute-solvent interactions are markedly decreased. The present account discusses the nature and properties of cryptate cations; the available information indicates that for a suitable cryptandcation pair, the enclosed metal cation is effectively shielded from the environment. Cryptate formation allows the stabilization of unusual species (metal anions, unstable oxidation states, etc) and markedly influences chemical reactivity, either inducing anion activation or inhibiting cation participation. It represents a tool for studying ionic reactions in solution, while a the same time strongly affecting the usual course of reactions like acid-base equilibria, phase transfer catalysis, alkylations, additions to carbonyl groups, nucleophilic substitutions, carbanion reactions, anionic polymerizations, etc.