Porphyrin-containing molecular capsules : metal mediated dimerization of a bis-porphyrin cavity

Molecular systems that can enclose space in a controlled fashion are receiving active attention in the current literature.2 Noncovalent interactions and self-assembly protocols are emerging as alternatives superior to assemblies largely prepared by covalent synthesis. In particular, capsule systems that reversibly form have been predominantly based on hydrogen bonds. These include Rebeks' "sportsballs" which stem from the glycoluril building block; urea-functionalizedcalixarene dimers reported independently by Rebek, Bohmer, Reinhouldt and de Mendoza;2 and giant sperical arrays constructed from calizarene units.3 Metal ion coordination has also been explored as a means of host assembly and has been reviewed.4