A New Look at the Halogenation of Porphyrins

The present study describes the selective halogenation at the β- or meso-position of the porphyrin macrocycle. The reactions of deuteroporphyrin IX dimethyl ester, mesoporphyrin III dimethyl ester and their Cu(II) and Ni(II) complexes with N-bromosuccinimide or phenylselenyl chloride were investigated. It could be observed that when the bromination of deuteroporphyn IX dimethyl ester using NBS took place, the isolated products were the result of an electrophilic substitution in β-free porphyrin ring positions. Employing the same reagent for halogenating mesoporphyrin III dimethyl ester, which does not possess β-free position, different derivatives were obtained from the allylic bromination of the ethyl side chain. When phenylselenyl chloride was used as halogenating agent with deuteroporphyn IX dimethyl ester or its Cu(II) complex, in both cases the replacement of β-free hydrogen atoms by phenylselenyl group was afforded. When the Ni(II) mesoporphyrin III dimethyl ester was used the desired and selective replacement of meso hydrogen atoms of aromatic ring by chlorine atoms was obtained. The structural assignment of the porphyrin derivatives thus obtained was performed by high-resolution mass spectrometry and detailed analysis of the NMR spectra.