IRON OCTAETHYLTETRAAZAPORPHYRINS - SYNTHESIS, CHARACTERIZATION, COORDINATION CHEMISTRY, AND COMPARISONS TO RELATED IRON PORPHYRINS AND PHTHALOCYANINES

This paper describes the synthesis and characterization of a series of iron octaethyltetraazaporphyrin complexes and a comparison of these substances to related iron porphyrins and phthalocyanines. Experimental evidence provided by magnetic susceptibility measurements, H-1 NMR, EPR, and Mossbauer spectroscopies, cyclic voltammetry, and/or X-ray crystallography indicates the tetraazaporphyrin ligand is a stronger sigma-donor and pi-acceptor than is a porphyrin ligand. Due to its high sigma-basicity, the tetraazaporphyrin ligand stabilizes the unusual S = 3/2 spin state for iron in chloroiron(III) octaethyltetraazaporphyrin. Yet the high pi-acidity of the tetraazaporphyrin ligand shifts iron III/II redox potentials 400 mV positive of those for analogous iron porphyrins. In this sense, the tetraazaporphyrin macrocycle is more like a phthalocyanine than a porphyrin. Compared to phthalocyanines octaethyltetraazaporphyrins are readily soluble. The high solubility, unusual metal spin states, and positively shifted redox potentials of octaethyltetraazaporphyrins suggest that they may have better or unique catalytic properties than porphyrins or phthalocyanines.