1D AND 2D H-1-NMR STUDIES OF IRON(III) COMPLEXES ON GEOPORPHYRINS OF THE DEOXOPHYLLOERYTHROETIO STRUCTURAL TYPE DERIVED FROM OIL-SHALE

One- and two-dimensional H-1 NMR studies of low-spin iron(III) geoporp hyrins derived from the deoxophylloerythroetioporphyrin series (the oi l shale source) resulted in an unambiguous assignment of all resonance s. Deoxophylloerythroetioporphyrin (DPEP) and its 17-desethyl homologu e were isolated from dictyonema shale as vanadyl complexes. They were demetallated and subsequently converted into iron(III) porphyrins unde r mild conditions. The 17-propionic methyl ester analogue, i.e. deoxop hylloerythrin methyl ester, was synthesized for comparative studies. A spectroscopic probe to identify iron(III) isocyclic porphyrins was es tablished. The five-membered isocyclic ring induced considerable asymm etry in the spin density distribution at the 3e(k) bonding orbitals, p lacing the unpaired electron on the d(xz) orbital located along the N- 21-N-23 axis. The temperature dependence of the hyperfine shift is con sistent with the thermal equilibrium between two non-degenerated elect ronic states (d(xz))(2)(d(yz))(1)<->(d(xz))(1)(d(yz))(2). The new stru ctural factor generating the asymmetric spin density distribution in l ow-spin iron(III) porphyrin complex was determined. The hyperfine shif t pattern of high-spin iron(III) isocyclic geoporphyrins provided usef ul probes for their detection in iron geoporphyrin mixtures by H-1 NMR prior to their separation. Valuable information is derived from the n umber of observed signals of meso-protons and characteristic, extremel y downfield resonances of isocyclic ring hydrogens. Both features may be useful for the spectral identification of iron(III) porphyrins of t he DPEP series from geological materials of relatively low purity.