Remarkable paramagnetically shifted 1H and 2 H NMR spectra of iron(II) complexes of 2-aza-21-carbaporphyrin:: An evidence for agostic interaction

Iron(II) 2-aza-21-carbaporphyrins have been characterized by paramagnetically shifted H-1 and H-2 NMR spectra. The high-spin iron(II) complex (HCTPPH)(FeBr)-Br-11 displays the beta-H resonances which reflect the combination sigma and pi routes of spin density delocalization. The uniquely large isotropic shift of the inner H(21) hydrogen (812 ppm, 298 K) indicates an Fe-11-{C(21)-H} agostic interaction.