The Coordination Chemistry of Planar Pentadentate “Porphyrin-Like” Ligands

The coordination chemistry of pentadentate porphyrin-like ligands is reviewed. The review is largely limited to planar or near-planar unsaturated pentaaza macrocycles and is concerned with pentadentate or potentially pentadentate systems derived from pyrrole, pyridine, bipyridine, phenanthroline, and terpyridine. Some discussion, however, is devoted to novel nonporphyrin macrocycles containing fewer than five nitrogen atoms. Specifically excluded from review are complex binucleating systems as well as saturated ligands of the aza crown ether or cryptand type.