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

Facile nitrite reduction was achieved using [Fe(II)(HCTPPH)NO] as the starting compound to react with NaNO(2). Stoichiometric studies allow the isolation of both {Fe(NO)}(6) and {Fe(NO)}(7) nitrosyl complexes and provide insight into the proton and electron transfer processes during the nitrite reduction. Treating [Fe(CTPP)NO] with acid or oxidizing [Fe(HCTPP)NO] with AgClO(4) yields intermediate [Fe(HCTPP)NO](+). The conversion cycles starting from {Fe(NO)}(6) [Fe(CTPP)NO] to {Fe(NO)}(6) [Fe(HCTPP)NO][ClO(4)] then to {Fe(NO)}(7) [Fe(HCTPP)NO] and vice versa were constructed.