~1H NMR and EPR studies of the electronic structure of low-spin iron(III) isocyanide mesotetraphenylchlorin complexes: a (d_(xz),d_(yz))~4(d_xy)~1 configuration from 293 to 4 K

摘要

Reaction of (tetraphenylchlorinato)iron(III) chloride with eight equivalents of tert-butyl isocyanide and 2,6-xylyl isocyanide inthe presence of zinc amalgam afforded Fe(TPC)(t-BuNC)_2 1 and Fe(TPC)(2,6-xylylNC)_2 2, respectively. The synthesis and characterizationof the trifluoromethanesulfonato derivatives of (tetraphenylchlorinato)iron(III) 3, bis(tert-butyl isocyanide)(tetraphenylchlorinato)iron(III) 4, and bis(2,6-xylyl isocyanide)(tetraphenylchlorinato)-iron(III) 5 are re[prted: [Fe(TPC)]CF_3SO_3 3, [Fe(TPC)(t-BuNC)_2] CF_3SO_3 4 and [Fe(TPC)(2,6-xylylNC)_2]CF_3SO_3 5. The ~1H NMR isotropic shift at 20 deg C of the pyrrole protons of the two complexes 4 and 5, varied from 5 ppm for a 4 to 8 ppm for 5 rather thanthe expected -10 to -30 ppm, based onpreviously studied bis-ligated complexes of low-spin iron(III) chlorins. EPR spectra of [Fe(TPC)(t-BuNC)_2]CF_3SO_3 4 in solution are axial, with g_perpendicular = 2.15 and g_(||) = 1.97 at 4 K, #SIGMA#G~2 = 14.7. All physical properties are consistent with a low-spin iron(III) with an unusual ground-state configuration (d_(xz),d_(yz))~4(d_(xy))~1