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

Abstract

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−κ2-N(O)−N(O)} (2a) (Tp = BH(pyrazol-1-yl)3) was prepared from the reaction of TpRuCl2(NO) (1) with pyrazole in the presence of Et3N. The curious N−N bond distance was X-ray crystallographically determined to be 1.861(3) A 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)](BF4)2 (4a·(BF4)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 N2O. These findings would provide valuable information regarding the mechanism of NO reduction to N2O by NOR.