Reactivity of Reduced Nitroprusside, [Fe(CN)5NO]3-, toward Oxygen

VIDELA, M.; RONCAROLI, F.; SLEP, L. D.; OLABE, J. A.

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY

American Chemical Society

Año: 2007 vol. 129 p. 278 - 279

0002-7863

In the reaction of [Fe(CN)5NO]3- with O2 (4:1 stoichiometry), the nitroprusside ion [Fe(CN)5NO]2- (NP) was quantitatively produced. The rate law was -1/4d[Fe(CN)5NO3-]/dt = k2[Fe(CN)5NO3-][O2], with k2 = (3.5 ± 0.2) × 105 M-1 s-1 at 25.0 C. The rate was insensitive to pH (range 9-11) and ionic strength (I = 0.1-1 M). Excess cyanide was used for minimizing the production of [Fe(CN)4NO]2-, which appeared to be much less reactive. Addition of O2 to the NO group is proposed to generate peroxynitrite bound to Fe(III), which reacts rapidly with [Fe(CN)5NO]3- to yield [Fe(CN)5NO2]3-. Reaction between the latter radical ions leads to the final product, NP. Comparison with the autoxidation rates for other NO complexes reveals that the rate constants decrease with an increase in ENO+/NO, the redox potentials of the bound NO+/NO couples. Six-coordination appears to be necessary for attaining reasonable electrophilic rates for the NO ligand, as with other heme and non-heme complexes.