A cobalt-nitrosyl complex, [(BPI)Co(NO)(OAc)], 1 {BPI = 1,3-bis(2'-pyridylimino)isoindol} was prepared and characterized. Structural characterization revealed that the cobalt center has a distorted square pyramidal geometry with the NO group coordinated from the apical position in a bent fashion. The addition of dioxygen (O) to the dichloromethane solution of complex 1 resulted in the formation of nitro complex, [(BPI)Co(NO)(OAc)], 2. It was characterized structurally. Kinetic studies suggested the involvement of an associative mechanism. FT-IR spectroscopic studies suggested the formation of the intermediate 1a [(BPI)Co(NO)(O)(OAc)] in the reaction. The intermediate 1a decomposed to complex 2 via a presumed peroxynitrite intermediate which was implicated by its characteristic phenol ring nitration reaction.

A Co(II) complex, [Co(L)]Cl, 1 of the ligand L (L = bis(2-ethyl-4-methylimidazol-5-yl)methane) upon reaction with HO in methanol solution at -40 °C resulted in the formation of the corresponding Co(III)-peroxo complex [Co(L)(O)] (2). The addition of NO gas to the freshly generated solution of the complex 2 led to the formation of the Co(II)-nitrato complex 3 through the putative formation of a Co(II)-peroxynitrite intermediate, 2a. The intermediate 2a was found to mediate the nitration of the externally added phenol resembling the nitration of tyrosine in biological systems.

A nitrosyl complex of MnII-porphyrinate, [(F20TPP)­MnII(NO)], 1 (F20TPPH2 = 5,10,15,20 tetrakis(pentafluorophenyl)­porphyrin), was synthesized and characterized. Spectroscopic and structural characterization revealed complex 1 as a penta-coordinated MnII-nitrosyl with a linear Mn–N–O (180.0°) moiety. Complex 1 does not react with O2. However, it reacts with superoxide (O2 –) in THF at −80 °C to result in the corresponding nitrate (NO3 –) complex, 2, via the formation of a presumed MnIII-peroxynitrite intermediate. ESI-mass spectrometry and UV–visible and X-band EPR spectroscopic studies suggest the generation of MnIV-oxo species in the reaction through homolytic cleavage of the O–O bond of the peroxynitrite ligand as proposed in NOD activity. The intermediate formation of the MnIII-peroxynitrite was further supported by the well accepted phenol ring nitration which resembles the biologically well-established tyrosine nitration.

The cobalt porphyrin complex [(ClTPP)Co], 1, {ClTPP = 5,10,15,20-tetrakis(4'-chlorophenyl)porphyrinate dianion} in dichloromethane solution was subjected to react with nitric oxide (NO) gas and resulted in the formation of the corresponding nitrosyl complex [(ClTPP)Co(NO)], 2, having {CoNO} description. It was characterized by spectroscopic studies and single-crystal X-ray structure determination. It did not react with dioxygen. However, in CHCl/CHCN solution, it reacted with HO to result in the Co-nitrito complex [(ClTPP)Co(NO)], 3, with the simultaneous release of O. It induced ring nitration to the added phenol in an appreciable yield. The reaction presumably proceeds through the formation of corresponding Co-peroxynitrite intermediate.

The reaction of a cobalt porphyrin complex, [(F 8 TPP)Co], 1 {F 8 TPP = 5,10,15,porphyrinate dianion} in dichloromethane with nitric oxide (NO) led to the nitrosyl complex, [(F 8 TPP)Co(NO)], 2. Spectroscopic studies and structural characterization revealed it as a bent nitrosyl of {CoNO} 8 description. It was stable in the presence of dioxygen. However, it reacts with H 2 O 2 in acetonitrile (or THF) solution at −40 °C (or −80 °C) to result in the corresponding Co(III)-nitrate complex, [(F 8 TPP)Co(NO 3 )], 3. The reaction presumably proceeds via the formation of a Co-peroxynitrite intermediate. X-Band electron paramagnetic resonance and electrospray ionization−mass spectroscopic studies suggest the intermediate formation of the [(porphyrin)Co(III)−O • ] radical, which in turn supports the generation of the corresponding Co(IV)-oxo species during the reaction. This is in accord with the homolytic cleavage of the O−O bond in heme-peroxynitrite proposed in the nitric oxide dioxygenases activity. In addition, the characteristic peroxynitrite-induced phenol ring reaction was also observed.