Syntheses and some chemistry of stable isoporphyrin systems

Abstract

Isoporphyrin zinc(II) complexes can be synthesized using the MacDonald ["2+2"] approach, with suitably substituted dipyrromethanes and 5,5-dialkyldipyrromethanes. The zinc(II) complexes are stable, show characteristic optical and1H NMR spectra, and have been characterized as perchlorate salts by X-ray diffraction. Attempts to prepare other metal salts of isoporphyrins ( Ni , Cu , Fe ), either by metalation during ring synthesis or by subsequent metalation of metal-free isoporphyrins, were unsuccessful. Evidence shows that a metal-free isoporphyrins can synthesized by demetalating the corresponding zinc(II) complexes with TFA. However, workup with base after the reaction must be avoided. The optical spectra of relatively unstable metal-free isoporphyrins (λmax( CH2Cl2) 430, 700 nm) are blue shifted relative to their zinc(II) complexes (λmax( CH2Cl2) 416, 731, 797 nm), and can be remetalated with zinc(II) acetate, to generate the fully characterized zinc(II) salts.