Fluoride Ion Coordination Chemistry of Iron(II) Porphyrins: Unique Spectral Properties and Associated Dioxygen Activation Chemistry of the Fluoroiron(II) Complex

Article abstract of DOI:10.1021/ja00199a013

Fluoroiron(II) porphyrin anionic complexes are generated in a variety of organic solvents by addition of tetrabutylammonium fluoride to the respective square-planar iron(II) porphyrin.The paramagnetic fluoroiron(II) tetraphenylporphyrin pyrrole proton NMR chemical shift value of 30.3 ppm resembles that for the corresponding hydroxide ion complex and is consistent with a high-spin iron(II) configuration.This even-spin complex surprisingly exhibits a broad 750 G X-band EPR signal at liquid helium temperature.Such a signal is expected only for a complex with alow-symmetry ligand field component.A very large Moessbauer quadrupole splitting parameter of 4.06 mm/s (78 K) serves to demonstrate further the strong ligand field perturbation by an axial fluoride ligand.The five-coordinate fluoroiron(II) porphyrin complex also exhibits unique reactivity with dioxygen, in that the detectable products at ambient temperature are the peroxoiron(III) porphyrin and the difluoroiron(III) porphyrin anionic complexes.This observation is in contrast to the usual dioxygen conversion of simple iron(II) porphyrins to the dinuclear oxo-bridged iron(III) porphyrin.