Peroxo and ferryl intermediates detected by 1H NMR spectroscopy during the oxygenation of iron(II) porphycene.

The iron(III) 2,7,12,17-tetra-n-propylporphycene (TPrPc)FeIIICl is reduced using aqueous sodium dithionite or zinc amalgam to produce (TPrPc)FeII. The 1H NMR spectrum of (TPrPc)FeII (293 K; delta (ppm): pyrrole, -37.52; meso, 71.56; alpha-CH2, 27.47; beta-CH2, 8.92; gamma-CH3, 5.55) can be accounted for by the planar unligated iron(II) porphycene with an S = 1 ground electronic state. Introduction of dioxygen into a toluene-d8 solution of (TPrPc)FeII at 203 K results in the formation of the (mu-peroxo)diiron(III) porphycene (TPrPc)FeIII-O-O-FeIII(TPrPc). The value of the chemical shift of the pyrrole resonances (17.99 ppm at 203 K) of this species and its distinct non-Curie behavior imply strong antiferromagnetic iron(III)-iron(III) coupling via a mu-peroxo bridge. The (TPrPc)FeIII-O-O-FeIII(TPrPc) intermediate is stable at 203 K, but it converts into the (mu-oxo)diiron complex (TPrPc)FeIII-O-FeIII(TPrPc) upon warming above 203 K. Reaction of (TPrPc)FeIII-O-O-FeIII(TPrPc) with a nitrogen bases (B: pyridine-d5, 1-methylimidazole) results in a homolytic cleavage of the mu-peroxo bridge to form the ferryl porphycene complex B(TPrPc)FeIVO (1H NMR (223 K), delta (ppm): pyrrole, -1.32; meso, 11.80). B(TPrPc)FeIVO reacts with triphenylphosphine at 223 K to yield triphenylphosphine oxide.