Low-spin organoiron(III) N-confused pyriporphyrin

Oxidation of (PyPH)(FeBr)-Br-II, an iron(II) complex of 6,11,16,21-tetraaryl-3-aza-m-benziporphyrin (N-confused pyriporphyrin, (PyPH)H) has been followed, in the presence of pyridine, by H-1 and H-2 NMR spectroscopy. One-electron oxidation with dioxygen, accompanied by deprotonation of a C(22)H fragment and formation of a Fe-C(22) bond, produced a low-spin, six-coordinate iron(HI) complex [(PyP)Fe-III(py)(2)](+) as confirmed by combination of H-1 NMR, EPR and structural data. The characteristic patterns of H-1 NMR pyrrole and meso-aryl resonances resemble features assigned to the less common, low-spin ground electronic state ((d(xz)dy(yz))(4)(d(xy))(1)) of iron(III) regular porphyrins. A conformational rearrangement process has been detected which involves two structures differentiated by macrocyclic ruffling. The structure of {H[(PyP)Fe-III(py)(2)](2)}(FeBr4)-Br-III)(3).CH2Cl2 has been determined by X-ray crystallography. The cationic complex involves a six-coordinate iron atom bound to the N-confused pyriporphyrin through its three nitrogens (Fe-N(23) = 1.924(7), Fe-N(24) 1.979(7), Fe-N(25) = 1.9343(7) angstrom) and the pirydyl trigonal C(22) atom (Fe(1)-C(22) = 1.972(10) angstrom). The porphyrin is strongly ruffled, defining two deep grooves along C-meso-C-meso axes at right angles to each other. Two axial pyridine ligands are located in the prearranged equatorial ligand grooves. The iron lies in the N3C plane of the macrocycle defined by coordinating nitrogen and carbon atoms. In the solid, pairs of molecules are positioned along the fine defined by Fe(1)-C(22) and Fe(2)-C(91) bonds. The structure demonstrates the head-to-head arrangement of two [(PyP)Fe-III(py)(2)](+) subunits revealing the adjacency of the two perimeter nitrogen atoms (the N(3)...N(72) distance = 2.587(10) angstrom) linked by the N...H...N hydrogen bond. Copyright (c) 2007 Society of Porphyrins & Phthalocyanines.