Fixation of One of Imidazole Ligands in Low Spin Bis-imidazole Ferric Porphyrin Complexes

Abstract Low spin ferric porphyrin complexes carrying rapidly rotating 1-methylimidazole and rotationally fixed 2-isopropylimidazole have been prepared. Chemical shift range of the pyrrole protons at −56 °C was nearly twice as much as that of the bis(hindered imidazole) complex. Orientation of the fixed ligand relative to the porphyrin plane was determined based on the splitting pattern of the meso-13C signals.