Metallacycles derived from metal complexes of exo-coordinated macrocyclic ligands

• Exo-coordination of macrocyclic ligands can be employed to build extended metallo-supramolecular structures.
• These include a range of dinuclear and oligonuclear metallacyclic species.
• A number of supramolecular interactions may help stabilize such individual metallacyclic structures.
• Larger cationic metallocycles may act as hosts for guest anions in their central cavities.

The assembly of metallacyclic structures incorporating exo-coordinated macrocyclic ligand components is reviewed. The exo-coordination approach provides a means for building extended cyclic assemblies and contrasts with the use of conventional endocyclic macrocyclic coordination which generally results in metal-in-cavity products. The approach, which depends on the availability of one or more donor atoms bearing electron lone pairs that are oriented exo to their macrocyclic cavity, has been employed to produce a range of diverse metallacyclic structures; examples of such metallo-assemblies displaying cyclic dimeric, trimeric, tetrameric, and hexameric topologies are presented.

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