Lewis Acid Activation of the Ferrous Heme-NO Fragment toward the N-N Coupling Reaction with NO To Generate NO.

Bacterial NO reductase (bacNOR) enzymes utilize a heme/non-heme active site to couple two NO molecules to NO. We show that BF coordination to the nitrosyl O-atom in (OEP)Fe(NO) activates it toward N-N bond formation with NO to generate NO. N-isotopic labeling reveals a reversible nitrosyl exchange reaction and follow-up N-O bond cleavage in the NO formation step. Other Lewis acids (B(CF) and K) also promote the NO coupling reaction with (OEP)Fe(NO). These results, complemented by DFT calculations, provide experimental support for the cis: b pathway in bacNOR.