O2 and CO Binding Behavior of Double-Sided Porphyrinatoiron(II) Complexes Modified by Amide Residues

New double-sided porphyrinatoiron(II) complexes having a polar cavity which includes an amide moiety (5,10,15-tris[2,6-bis(3,3-dimethylbutyryloxy)phenyl]-20-[2-[N-acetylvalyloxy]-6-(3,3-dimethylbutyryloxy)phenyl]porphinatoiron(II) (1b) and 5,10,15-tris[2,6-bis(3,3-dimethylbutyryloxy)phenyl]-20-[2-[3,5-bis(acetamido)benzoyloxy]-6-(3,3-dimethylbutyryloxy)phenyl]porphinatoiron(II) (2b)) were synthesized. 1H NMR spectroscopy indicated that the amide residues are located on the porphyrin ring plane. The O2 and CO binding affinities of 1b and 2b were higher than those of 5,10,15,20-tetrakis[2,6-bis(3,3-dimethylbutyryloxy)phenyl]porphinatoiron(II) (4b), in response to the local polarity in the cavity. The polar amide residue resulted in a decreased O2 dissociation rate. Thermodynamic parameters for the gaseous ligand bindings to the 2b complex were also determined.