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The preparation of the title compound, a model for the active site of oxygen carrier hemoproteins, is described and the kinetic parameters of the CO and O2 adducts show the importance of the co-ordinated imidazole in stabilization.

The observation of a new resonance in the 13C n.m.r. spectrum of a high spin iron(III)meso-tetraphenylporphyrin, the resolution of previously unresolved spin–spin splittings, and the synthesis of a 13C enriched porphyrin permit a complete reassignment of the spectrum which shows unexpectedly large paramagnetic shifts of the ortho phenyl carbon resonances previously assigned to pyrrolic carbon signals.

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.

The synthesis of the ‘both-faces’ hindered porphyrins using two different methods is reported. These so-called ‘basket-handle’ porphyrins (BHP) are derived from 5,10,15,20-tetraphenylporphyrin in which two opposite phenyl groups are bridged by alkylene or arylene-p-bisalkylene chains. In addition to the desired compounds [the cross-trans-linked isomer (7)], two other isomers were obtained [adjacent-trans-linked (8) and adjacent-cis-linked (9)]. These were separated by t.l.c. on silica gel and then individually characterized. The structural assignment of the three isomers in the five series studied was based on the 1H n.m.r. spectra of the free bases and of their iron(II) complexes.