Reaction of a Co(iii)-peroxo complex with nitric oxide: putative formation of a peroxynitrite intermediate

Abstract

A Co(II) complex, [Co^II(L)₂(H₂O)₂](ClO₄)₂, 1, having a bidentate ligand L [L = bis(3,5-dimethylpyrazolyl)methane] has been synthesized. Complex 1 in acetonitrile solution at −40 °C, in the presence of H₂O₂ and NEt₃, afforded the corresponding Co(III)-peroxo species, [Co^III(L)₂(O₂²⁻)]⁺, as the transient intermediate 1a. Thermal instability precluded its isolation and further characterization. The addition of nitric oxide (NO) gas into the freshly prepared [Co^III(L)₂(O₂²⁻)]⁺ in acetonitrile at −40 °C resulted in the corresponding Co(II)-nitrato complex, [Co^II(L)₂(NO₃)](ClO₄) (2). The reaction is proposed to proceed through a putative Co(II)-peroxynitrite intermediate 1b. It was evidenced by the characteristic phenol ring nitration reaction.