Binding of dioxygen in a picket-fence porphyrin complex of iron. A theoretical QM/MM study

Abstract

The hybrid quantum mechanics/molecular mechanics method IMOMM is applied to the calculation of the structure of the oxygenated picket-fence porphyrin complex of iron Fe(T_pivPP)(1-MeIm)(O₂), with results in good agreement with available X-ray data. An investigation on the role of the picket-fence substituents in the binding of dioxygen through comparison with additional calculations on a system with the "‘naked’' porphyrin complex Fe(P)(1-MeIm)(O₂) shows that the presence of the amide groups of the picket-fences contribute to the binding with ca. 5 kcal mol^-1. The largest contribution to this stabilization is found to correspond to an O···H(N) interaction.