Both-faces hindered porphyrins. Part 3. Synthesis and characterization of internally five-co-ordinated iron(II) basket handle porphyrins derived from 5,10,15,20-tetrakis(o-aminophenyl)porphyrin

Abstract

The synthesis of a series of so-called amide ‘hanging base’ porphyrins (10), (14) and (18). derived from 5,10,15,20-tetrakis(o-aminophenyl)porphyrin (αβαβ-atropisomer)(3), in which one of the faces is hindered by an alkylene or an arylene-p-bisalkylene bridge and the other face is bridged by a pyridine-3,5-diyl-bisalkyleneoran imidazolyl-alkylene chain, is described. The structural assignment of the various compounds is based on the ¹H n.m.r. spectra of the free bases, and of their zinc(II) and iron(II) complexes. Unlike the ether ‘hanging base’ metalloporphyrins, the metallic ion of amide ‘hanging base’ porphyrins is actually five-co-ordinated by the proximal base. Furthermore, not only is the equilibrium pyridine plane orientation dependent on the length of its linking chain, but the bridging forces the amide protons to point toward the centre of the macrocyle core. These structural properties are potential factors which may affect the binding of dioxygen. The synthesis of a bis-pyridine ‘basket handle’ porphyrin is also reported.