Metal Complexes ofmeso-Amino-octaethylporphyrin and the Oxidation of NiII(meso-amino-octaethylporphyrin)

Abstract

The crystal structures of meso-NH2−OEPH2, NiII(meso-NH2−OEP), and CuII(meso-NH2−OEP) (where OEP is the dianion of meso-amino-octaethylporphyrin) have been determined to examine the effects of the meso-substituent on the geometry of the ligand. CuII(meso-NH2−OEP) has a nearly planar geometry while the free ligand itself and NiII(meso-NH2−OEP) have ruf conformations. NiII(meso-NH2−OEP) is much less reactive toward oxidation than are (py)2FeII(meso-NH2−OEP), ClFeIII(meso-NH2−OEP), or NiII(meso-HO−OEP), which all undergo oxidation in pyridine solution when exposed to dioxygen. Treatment of NiII(meso-NH2−OEP) with iron(III) chloride in chloroform solution does result in oxidation of the ligand in two separate processes. One involves oxygenation at the trans-meso position, while the other results in ring cleavage and removal of the amino function. The open-chain tetrapyrrole complex, NiII(OEB−CO2Et), has been characterized by single-crystal X-ray diffraction and shown to contain a helical ligand with a four-coordinate nickel ion.