Fixation of Zinc(II) Ion to Dioxygen in a Highly Deformed Porphyrin: Implications for the Oxygen Carrier Mechanism of Distorted Heme

Three saddle-type nonplanar zinc porphyrins strapped by two short alkyl linkers have been synthesized. The deformation induced by the linkers can cause a spectral red shift of >30 nm compared with the absorption maxima of regular porphyrins and can also regulate the electronic structure of the central zinc(II) ion. The zinc(II) ion then complexes and activates a free dioxygen to form a superoxide group ligand by enlarging the splitting of energy levels of d orbitals under strong core deformation. The fixation of dioxygen can be reasonably explained by the Dewar-Chatt-Duncanson model. These results indicate that this type of saddle porphyrin has the potential to be used as a new model system of heme.