Remarkable Paramagnetically Shifted 1H and 2H 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 1H and 2H NMR spectra. The high-spin iron(II) complex (HCTPPH)FeIIBr 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 FeII-{C(21)-H} agostic interaction.