Spontaneous nucleophilic addition of hydroxide ions to the meso-position of high-valent antimony-ore porphyrin complexes

Bimolecular reactions of the antimony(V) porphyrin complexes SbO(tpp)OH, 1 and SbO(oep)OH. 2 with tetra-n-butylammonium hydroxide were investigated at 298 K in acetonitrile solution (tpp, dianion of 5,10,15,20-tetraphenylporp hyrin and oep, dianion of 2,3,7,8,12,13,17,18-octaethylporphyrin). Spontane ous nucleophilic addition of hydroxide ions to the non-oxidized porphyrin m acrocycle leads to novel hydroxyphlorin derivatives, which contain a satura ted meso-carbon bridge. While this process is a reversible equilibrium reac tion for the TPP derivative, the OEP complex undergoes subsequent demetalla tion and oxidative ring cleavage in the presence of dioxygen. Possible impl ications for the competitive inhibition of heme-oxygenase by high-valent me talloporphyrin therapeutics are discussed. (C) 2001 Elsevier Science B.V. A ll rights reserved.