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)(FeCl)-Cl-III is reduced using aqueous sodium dithionite or zinc amalgam to produce (TPrPc)Fe-II. The H-1 NMR spectrum of (TPrPc)Fe-II (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-d(8) solution of (TPrPc)Fe-II at 203 K results in the formation, of the (mu-peroxo)diiron(III) porphycene (TPrPc)Fe-III-O-O-Fe-III(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)Fe-III-O-O-Fe-III(TPrPc) intermediate is stable at 203 K, but it converts into the (mu-oxo)diiron complex (TPrPc)Fe-III-O-Fe-III(TPrPc) upon warming above 203 K. Reaction of (TPrPc)Fe-III-O-O-Fe-III(TPrPc) with a nitrogen bases (B: pyridine-d(5), 1-methylimidazole) results in a homolytic cleavage of the mu-peroxo bridge to form the ferryl porphycene complex B(TPrPc)(FeO)-O-IV (H-1 NMR (223 K), delta (ppm): pyrrole, -1.32; meso, 11.80). B(TPrPc)(FeO)-O-IV reacts with triphenylphosphine at 223 K to yield triphenylphosphine oxide.