Reversible N−N Coupling of NO Ligands on Dinuclear Ruthenium Complexes and Subsequent N2O Evolution: Relevance to Nitric Oxide Reductase

Unprecedented N−N coupling of two nitrosyl ligands on dinuclear complexes was discovered, which is proposed as a critical step in the bacterial NO reductase (NOR). The N−N coupled complex (TpRu) 2 (μ-Cl)(μ-pz){μ−κ 2 -N( O)−N( O)} ( 2a ) (Tp = BH(pyrazol-1-yl) 3 ) was prepared from the reaction of TpRuCl 2 (NO) ( 1 ) with pyrazole in the presence of Et 3 N. The curious N−N bond distance was X-ray crystallographically determined to be 1.861(3) Å for the N−N coupled analogue with a 4-methylpyrazolato bridge, and was confirmed by DFT calculation. The N−N bond of 2a was cleaved by oxidation to give [{TpRu(NO)} 2 (μ-Cl)(μ-pz)](BF 4 ) 2 ( 4a ·(BF 4 ) 2 ), which on reduction reformed 2a . It is interesting to note that the N−N coupled complex 2a was also transformed into the oxo-bridged dinuclear species 5a with the evolution of N 2 O. These findings would provide valuable information regarding the mechanism of NO reduction to N 2 O by NOR.