Rapid and Selective Oxidation of Metallo-Sulphophthalocyanines Prior to Their Usefulness as Precatalysts in Oxidation Reactions

Two metallosulfophthalocyanines, RuPcS and FePcS, used in many catalytic oxidation reactions, were readily oxidized by hydrogen peroxide or monopersulfate, under acidic or neutral conditions in water, to form novel metal complexes derived from the facile oxidation of the PcS ring. Meso-nitrogen-oxide derivatives and metal-biliverdin-like derivatives were identified among the products at early reaction times, whereas at longer times fragmentation of the phthalocyanine ring occurred, with formation of sulfophthalimide and metal complexes containing the resulting tridentate ligand. The oxidative degradation of the MPcS complexes has been investigated by ESI-MS, UV/Vis-NIR and H-1, C-11 and N-15 NMR spectroscopy. These rapidly formed, coordinatively unsaturated complexes represent the dominant species in oxidizing media, at least in the case of the Ru derivative, and must be the real catalyst precursors in previously published oxidation reactions using MPcS complexes. The oxidative degradation reactions occurred with selective mono-denitrogenation of one meso-nitrogen atom and formation of ammonia, thus recalling the celebrated selective degradation of heme to verdoheme and/or biliverdin and CO.