Effect of Phosphorus Axial π-Acceptors in Iron(III) Porphyrinates: Characterization of Low-Spin Complexes [(PPh(OMe)2)2Fe(T(p-Me)PP)]CF3SO3 and [(PPh(OEt)2)2Fe(T(p-Me)PP)]CF3SO3

Abstract

The synthesis and characterization of the trifluoromethanesulfonato derivatives of bis(dimethyl phenylphosphonite)(tetrakis(p-methylphenyl)porphyrinato)ironIII, 1, and bis(diethyl phenylphosphonite)(tetrakis(p-methylphenyl)porphyrinato)ironIII, 2, are reported: [(PPh(OMe)2)2Fe(T(p-Me)PP)]CF3SO3, 1, and [(PPh(OEt)2)2Fe(T(p-Me)PP)]CF3SO3, 2, (T(p-Me)PP = tetrakis(p-methylphenyl)porphyrinato). The crystal structure of complexes 1 and 2 have been determined. Both X-ray structures show that the porphyrinate rings are strongly ruffled. The equatorial Fe−N bond distances average to 1.971 (6) A for 1 and to 1.969 (7) A for 2, which is a quite short distance for low-spin ironIII porphyrinate derivatives. The 1H NMR isotropic shifts at 20 °C of the pyrrole protons of the two complexes, varied from −2 ppm for 2 to +3 ppm for 1 rather than the expected −20 to −30 ppm, based on previously studied bis-ligated complexes of low-spin ferric porphyrins. The electron paramagnetic resonance spectra of [(PPh(OMe)2)2Fe(T(p-Me...