Calix[4]pyrrole Schiff Base Macrocycles. Novel Binucleating Ligands for μ-Oxo Iron Complexes

New bimetallic μ-oxo diferric complexes of several previously reported calix[4]pyrrole Schiff base macrocycles are
described. The synthesis of a new member of this class of macrocycles is also reported; it was prepared via an
acid-catalyzed condensation between 1,9-bisformyl-5,5-dipropyldipyrromethane and o-phenylenediamine. Reactions
of the free base macrocycles or their bis-HCl salts with Fe(II) mesitylene, followed by air oxidation, gave the
binuclear μ-oxo bis-Fe(III) compounds 6−10 in moderate yield. X-ray crystallography data reveal two different
coordination environments for the Fe−O−Fe subunit in 6−10 that it is suggested can be controlled by altering the
reaction conditions. Structural properties of these metalated pyrrolic macrocycles are also compared to those of
μ-oxo diferric porphyrins and μ-oxo diferric texaphyrin. Complexes 6−10 exhibit two distinct types of M−N bonds
that are similar in length to the bonds observed in metallotexaphyrin complexes. However, the electronics of the
present systems are very different from those of texaphyrins and porphyrins in that no delocalized bonding patterns
are observed within the ligands as a whole.