Oxygenation Patterns for Substituted meso-Tetraphenylporphyrin Complexes of Iron(II). Spectroscopic Detection of Dioxygen Complexes in the Absence of Amines

Article abstract of DOI:10.1021/ja00386a027

The reaction of dioxygen with iron(II) porphyrins in inert solvents has been studied by 1H NMR spectroscopy in order to detect the presence of reactive intermediates.Sterically hindered porphyrins have been examined in which the formation of peroxo- and oxo-bridged dimeric structure is limited.The iron(II) porphyrins studied have 1H NMR spectra characteristic of intermediate-spin (S = 1), four-coordinate species.Reduction of iron(III) chloride (Fe^IIICl) or iron(III) chloride (Fe^IIICl) with either aqueous sodium dithionite or zinc amalgam in dichloromethane solution produces Fe^II or Fe^II.The previously reported reduction of these two porphyrins with piperidine has been reexamined and shown to form the bis(pipridine) adducts of the iron(II) porphyrins.Addition of dioxygen to paramagnetic iron(II) (Fe^II) in toluene solution below -70 deg C produces a new diamagnetic complex that is formulated as FeO2. 1H NMR spectroscopic observations indicated that, on warming, this species is successively converted to Fe^IIIO2Fe^III and to Fe^IIIOFe^III.The latter has been previously isolated.Reaction of FeO2 with N-methylimidazole (N-MeIm) at -70 deg C results in the formation of (N-MeIm)FeO2.Addition of oxygen to Fe^II at -70 deg C in toluene solution results in the formation of diamagnetic FeO2.This, on warming, is converted to FeO2Fe and then to FeOH and FeOFe as the final stable products.Addition of dioxygen to Fe^II and Fe^II in dichloromethane solution at -70 deg C produces diamagnetic dioxygen adducts.On warming, these undergo dissociation to form the parent iron(II) complex and irreversible oxidation to form iron(III) porphyrin hydroxide and chloride.