The Self-Assembly of Cryptophanes

Jean-Claude Chambron

ICMUB, UMR 6302, CNRS, Univ. Bourgogne Franche-Comté, F-21078 Dijon

Cryptophanes are cage-like cyclophanes made from two triply-bridged concave substituted cyclotribenzylene (CTB) derivatives, which can encapsulate various substrates, from atoms (Xe, Cs⁺, Tl⁺) to molecules (alkanes, haloalkanes, quaternary ammoniums, fullerenes), depending on the nature of the substituents and the bridges. They are traditionally obtained by multistep organic synthesis as separable mixtures of meso and chiral diastereomers, the occurrence of complete diastereoselectivity towards either stereoisomer being frequently observed. Rare, however, are examples of cryptophanes obtained under thermodynamic control, using either reversible covalent or labile coordination bonds.

            In this lecture we shall present our own contribution to the latter approaches, that is, the generation of cryptophanes by tripod-tripod coupling of original functionalized CTBs using disulfide bridges on the one hand, and metal-nitrogen coordination bonds on the other hand. Template effects as well as stereochemical issues will be discussed, labile coordination bonds will also be compared to inert coordination bonds, the inorganic pendant of classical covalent bonds. Finally, dynamic combinatorial chemistry experiments based on either approach will be presented and commented.