Synthesis and O₂-binding properties of tetraphenylporphyrinato- iron(II) derivatives bearing a proximal imidazole covalently bound at the β-pyrrolic position

5,10,15,20-Tetrakis(o-pivalamidophenyl)porphyrins (TPVP) and their iron(II) derivatives bearing a proximal imidazole covalently bound at the 2-(β-pyrrolic) position have been synthesized. The visible absorption maxima (λ_max) of the 2-substituted TPVP with an electron withdrawing group attached is shifted toward the red region (7-11 nm) compared with that of the original TPVP. The iron(II) complexes having an imidazolyl group at the β-pyrrolic position were five coordinated species with an intramolecularly bound base under argon and reversibly formed a stable dioxygen adduct in response to O₂-pressure in toluene at 25 °C. These molecules act as efficient dioxygen carrying molecules. The kinetics of O ₂ binding to the 2-substituted Fe(TPVP) complexes are described.