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

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 degrees C, in the presence of H2O2 and NEt3, afforded the corresponding Co(III)-peroxo species, [Co-III(L)(2)(O-2(2-))](+), 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)(O-2(2-))](+) in acetonitrile at -40 degrees 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.