Metal mediated self-assembled porphyrin metallacycles: Synthesis and multipurpose applications

Over the last two decades the metal-mediated directional-bonding has established as an efficient tool for the construction of complex and functional supramolecular architectures. The success of this approach has strongly benefited from design principles based on the known and fixed ligand and metal coordina- tion geometry, thus ensuring a high level of control on the topology and energetics of the supramolecular adducts. Among them, self-assembled pyridylporphyrin metallacycles have attracted considerable atten- tion due to their symmetric structure, to their peculiar optical and redox properties, to their large inner cavity, that can be easily addressed by axial ligation to metal ions inserted in the porphyrin ring. This review is focused on this particular subset of metal–organic architectures and in particular on discrete metallacyclic system with a 4 + 4 and 2 + 2 metal/ligand stoichiometry formed by coordination of 4-pyr- idylporphyrins with different metal ions (Pd(II), Pt(II), Ru(II), Re(I)). Their synthesis, characterization and applications in the field of catalysis, molecular recognition, sensing and ionophoric behavior will be reviewed with the aim to stimulate further interest on these versatile supramolecular systems.