Bile pigment studies. Part 4. Some novel reactions of metalloporphyrins with thallium(III) and cerium(IV) salts. Ring cleavage of meso-tetraphenylporphyrin

Treatment of zinc(II)meso-tetraphenylporphyrin (5) with thallium(III) trifluoroacetate or nitrate, or cerium(IV) ammonium nitrate gives a mixture of the 5,15-dihydroxy-5,10,15,20-tetraphenylporphodimethenes (7), the 5-hydroxy-15-methoxy-derivatives (8), and the ring-opened bilinone (10) after acidic demetallation. An extra product when thallium(III) trifluoroacetate is employed is the trifluoroacetyl derivative (12) or (13). When thallium(III) nitrate or cerium(IV) ammonium nitrate are used, the β-nitro-meso-tetraphenylporphyrin (14) is also isolated. Nitration of zinc(II) octa-alkylporphyrins with these two salts is shown to be a general reaction which can be controlled to give mono- or di-nitration at the meso-positions. Mechanistic implications of the ring-cleavage and nitration reactions are discussed.