Not Limited to Iron: A Cobalt Heme-NO Model Facilitates N-N Coupling with External NO in the Presence of a Lewis Acid to Generate N O.

Some bacterial heme proteins catalyze the coupling of two NO molecules to generate N O. We previously reported that a heme Fe-NO model engages in this N-N bond-forming reaction with NO. We now demonstrate that (OEP)Co (NO) similarly reacts with 1 equiv of NO in the presence of the Lewis acids BX (X=F, C F ) to generate N O. DFT calculations support retention of the Co oxidation state for the experimentally observed adduct (OEP)Co (NO⋅BF ), the presumed hyponitrite intermediate (P )Co (ONNO⋅BF ), and the porphyrin π-radical cation by-product of this reaction, and that the π-radical cation formation likely occurs at the hyponitrite stage. In contrast, the Fe analogue undergoes a ferrous-to-ferric oxidation state conversion during this reaction. Our work shows that cobalt hemes are chemically competent to engage in the NO-to-N O conversion reaction.