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.