Zn(II), Ni(II), Cu(II), and Fe(III) complexes of potentially bimetalating tris(pyridine- and imidazole-appended) picket-fence naphthylporphyrins with benzyl ether spacers: implications for cytochrome c oxidase active-site modeling

Two new unsymmetrical picket-fence naphthylporphyrin ligands, 1 and 2, and several of their metalated porphyrinato complexes have been synthesized as precursor model compounds for the binuclear (Fe/Cu) cytochrome c oxidase (CcO) active site. 1 and 2 have a naphthylporphyrin superstructure that has been specifically incorporated to confer long-term configurational stability to the atropisomeric products. The two picket-fence porphyrin ligands also bear covalently linked, axially offset tris(heterocycle) coordination sites for a copper ion, much like that found in the native enzyme. Monometallic porphyrin complexes M = Zn(II), Ni(II), Cu(II), and Fe(III)] of the pyridine-appended ligand 1 have been prepared and spectroscopically and magnetically characterized. An unusual monomeric iron(III) hydroxo porphyrin complex was isolated upon workup of the compound formed under ferrous sulfate/acetic acid reflux conditions. There is general difficulty in forming binuclear complexes of 1, which is attributed to the conformational flexibility of the benzyl ether type picket spacers. The potential of ligands such as 1 and 2 for future CcO active-site modeling studies is considered.