REACTION OF METALLOPORPHYRINS WITH NITROGEN-DIOXIDE

The octaethylporphyrin(OEP) complexes of iron(III) chloride, iron(III) acetate, thallium(III) hydroxide, zinc(II), and cobalt(II) and the mesoporphyrin IX dimethyl ester (MPDME) complexes of zinc(II) and iron(III) chloride were reacted with a 20:1 ratio of NO2 to metalloporphyrin in CH2Cl2. The +3 metalloporphyrins gave products which had a nitromethyl group in each of the four meso positions of the porphyrin ring and a chloride ion bound to the metal atom. The products of +2 metalloporphyrin reaction had a nitro group bound in each of the meso positions. The spectral and electrochemical properties of some of the products were measured. 36Cl labelled OEPFeCl was reacted with NO2 in CH2Cl2. The product, meso-tetranitromethyl OEPFeCl, had 17% of the original activity which indicates that the chloride ion bound to the iron is exchanged with chloride ions formed in the reaction. The nitromethylation reaction appears to involve initially the displacement of chloride from iron(III) by NO2 and solvent attack on the bound NO2. The meso-nitration of the +2 metalloporphyrin by NO2 has been proposed to proceed by a π-cation radical mechanism (E.C. Johnson and D. Dolphin, Tetrahedron Letters 2197 (1976). © 1979.