Disproportionation of O‐Benzylhydroxylamine Catalyzed by a Ferric Bis‐Picket Fence Porphyrin Complex

Abstract

Hydroxylamine (NH 2 OH) is an important molecule in biology that serves as an intermediate in the nitrogen cycle, and that can also be utilized as a nitric oxide donor in mammals under certain conditions. In light of this, the interaction of NH 2 OH with hemes in proteins and model systems has gained much attention recently. In this study, we use the more stable, oxygen substituted O‐benzylhydroxylamine (NH 2 OBn) as a model for NH 2 OH. Here, the reactivity of the ferric bis‐picket fence porphyrin complexes [Fe(3, 5‐Me‐BAFP)(ClO 4 )] ( 1 ) and [Fe(3, 5‐Me‐BAFP)(PF 6 )] ( 2 ) (3,5‐Me‐BAFP 2– = dianion of tetra(2, 6‐bis(3,5‐dimethylphenoxy)phenyl)porphyrin)) with NH 2 OBn is investigated. The product of these reactions is characterized by UV/Vis and EPR spectroscopy and X‐ray crystallography. We found that addition of excess NH 2 OBn to our ferric porphyrin complexes results in reduction of the heme to the ferrous oxidation state. This is followed by disproportionation of additional NH 2 OBn to yield the ferrous complex [Fe(3,5‐Me‐BAFP)(NH 3 ) 2 ] ( 3 ) as the final product. The crystal structure of ( 3 ) constitutes the first structural characterization of a bis‐ammonia complex of a ferrous heme. The stability of this complex may be facilitated by the picket fences of the porphyrin ligand used here.