NUCLEAR-MAGNETIC-RESONANCE STUDIES OF THE FORMATION OF TERTIARY ALKYL COMPLEXES OF IRON(III) PORPHYRINS AND THEIR REACTIONS WITH DIOXYGEN

Iron(III) complexes of tetra-(p-tolyl)porphyrin (TTPH2) with axial adamantyl (1-ad), camphane (4-cam), and tert-butyl ligands have been prepared and characterized by NMR spectroscopy. These have typical properties for low-spin (S = 1/2), five-coordinate complexes. Analyses of the paramagnetic NMR spectral patterns for a variety of axial ligands are made and compared with those of aliphatic amines. These spectra exhibit sizeable dipolar shifts and can show non-Curie temperature dependence, particularly for the β-protons. Treatment of TTPFeIII(4-cam), TTPFeIII(1-ad), or TTPFeIII(t-Bu) with dioxygen in toluene at-70 °C; produces a mixture of TTPFeIIIOH, TTPFeIIIOFeIIITTP, and TTPFeIIIIOOR (R = tert-butyl, 4-cam, or 1-ad). The absence of hydrogen atoms in the α-carbon of these tertiary alkyl peroxide complexes alters their reactivity so that an intermediate formed by the O-O bond-breaking step can be detected. Treatment of TTPFeIIIOO(4-cam) with pyridine at-70 ° C results in its conversion into TTPFeIv =O through homolysis of the O-O bond. © 1990, American Chemical Society. All rights reserved.