Lewis Acid Activation of the Ferrous Heme-NO Fragment toward the N-N Coupling Reaction with NO to Generate N₂O

Bacterial NO reductase (bacNOR) enzymes utilize a heme/non-heme active site to couple two NO molecules to N₂O. We show that BF₃ coordination to the nitrosyl O-atom in (OEP)Fe(NO) activates it toward N-N bond formation with NO to generate N₂O. ¹⁵N-isotopic labeling reveals a reversible nitrosyl exchange reaction and follow-up N-O bond cleavage in the N₂O formation step. Other Lewis acids (B(C₆F₅)₃ and K⁺) also promote the NO coupling reaction with (OEP)Fe(NO). These results, complemented by DFT calculations, provide experimental support for the cis:b₃ pathway in bacNOR.