First Water-Soluble μ-Nitrido Dimer of Iron Phthalocyanine

Abstract

The μ-nitrido dimer of Fe-phthalocyanine μ-N(FePc)2 was first reported and actively studied in the middle of the 1980s.[1,2] Recently it was established that its tert-butyl substituted derivative μ-N(FePcBu4)2 catalyses the oxidation of methane by H2O2 under very mild conditions (25-60 oC),[3] and then a high catalytic activity was also demonstrated in the oxidation of other organic substrates.[4] It has been shown in theoretical work[5] that the ability of the μ-nitrido moiety to serve as a remarkable charge reservoir and to stabilise the lower spin-states can enhance the catalytic activity of μ-nitrido dimers of Fe-porphyrazines in comparison with the corresponding μ-oxo species. The water-soluble FeIIItetrasulfophthalocyanine in its μ-oxo form, μ-O(FeTSPc)2, catalyses various redox-reactions in aqueous medium.[6] Among μ-nitrido dimers so far only μ-N(FePcBu4)2 and other species well-soluble in organic solvents due to presence of alkyl residues were studied, including alkoxy[7] and alkylsulfonyl[8] substituted derivatives. We report here the synthesis of the first water-soluble derivative – the μ-nitrido dimer of Fe-tetrasulfophthalocyanine, μ-N(FeTSPc)2, which was prepared by two alternative routes (Scheme 1). In the first approach Fe-tetrasulfophthalocyanine, which was prepared by cyclotetramerization of 4-sulfophthalic acid,[9] was used as a starting material. In neutral or basic water solutions this species exists as μ-oxodimer μ-O(FeTSPc)2, [6]