PENDANT-CAPPED PORPHYRINS .1. THE SYNTHESIS OF A BIPHENYL PENDANT-CAPPED IRON(III) PORPHYRIN MODEL OF CATALASE

A phenol pendant-capped porphyrin ((PHPCP)H2) and its iron(III) complex ((PPCP)Fe(III)) have been synthesized. H-1 and C-13 NMR were used to characterize all intermediates leading to the final product. In addition, the heteronuclear C-13-H-1 shift correlation experiment was used to further characterize the tetraaldehyde precursor of the pendant-capped porphyrin. Proton and carbon chemical shifts for the free base porphyrin (PHPCP)H2 were assigned by using one-dimensional NMR experiments (including C-13 APT) and two-dimensional homonuclear COSY and ROESY experiments. In (PHPCP)H2, the phenol that provides the ligand is hung from the ceiling of a vaulted dome or tepee with protected walls supported by four legs that are anchored to the 2-position of the phenyl rings at the 5,10,15,20-meso-carbons of (TPP)H2. In the ground-state structure of (PPCP)Fe(III), the phenol is dissociated such that the resultant phenolate species is ligated to the high-spin (S = 5/2) iron(III). Ligation of phenolate and iron moieties is established by (i) comparison of H-1 NMR to the H-1 NMR of the phenolate complex of [(TPP)Fe(III)]+; (ii) comparison of the UV/vis spectrum to that for the phenolate complex of [(TPP)Fe(III)]+; (iii) disappearance of the O-H stretch in the IR accompanying complexation of (PHPCP)H2 with Fe(III); and (iv) laser desorption mass spectroscopy. At the active site of catalase, the protoporphyrin-IX iron(III) is ligated to the phenolate form of a tyrosine residue.