Both-faces hindered porphyrins. Part 5. Synthesis and characterization of iron(III) basket handle porphyrins having multiple secondary amide groups inserted in the superstructures
The synthesis of basket handle porphyrins in a cross-trans configuration (27) and (28) derived from 5,10,15,20-tetrakis(o-aminophenyl)porphyrin, and their hydroxy-iron(III) complexes, in which one of the faces is hindered by a bridge substituted by one or two amino-acids (L-phenylalanine or L-valine) and with the other face protected by a hanging-imidazole chain is described. The synthetic methodology for these compounds allows the preparation of other superstructured porphyrins containing several amino acids in the handles; this gives an increasing number of secondary amide groups in the vicinity of the metallic centre. Structural assignments for the various compounds were made on the basis of the 1H n.m.r. spectra of the free bases. The optical purity of the compounds was established by g.i.c. on a chiral phase. Absorption spectra of hydroxy-iron(III) derivatives of hanging imidazole basket handle porphyrins display an unusual pattern consistent with the presence of water partially co-ordinated to the metallic ion and stabilized in the distal cavity by a hydrogen bond formed between water proton(s) and the carbonyl group of the ‘peptide’ bond.