Simultaneous nitrosylation and N-nitrosation of a Ni-thiolate model complex of Ni-containing SOD.

Nitric oxide (NO) is used as a substrate analogue/spectroscopic probe of metal sites that bind and activate oxygen and its derivatives. To assess the interaction of superoxide with the Ni center in Ni-containing superoxide dismutase (NiSOD), we studied the reaction of NO and NO with the model complex, EtN[Ni(nmp)(SPh--NH--CF)] (; nmp = dianion of -(2-mercaptoethyl)picolinamide; SPh--NH--CF = 2-amino-4-(trifluoromethyl)benzenethiolate) and its oxidized analogue , respectively. The ultimate products of these reactions are the disulfide of SPh--NH--CF and the ,-bridged tetrameric complex [Ni(nmp)], a result of S-based redox activity. However, introduction of NO to affords the green dimeric {NiNO} complex (EtN)[{Ni(κ-Ph-NO--CF)(NO)}] () NO-induced loss of nmp as the disulfide and N-nitrosation of the aromatic thiolate. Complex was characterized by X-ray crystallography and several spectroscopies. These measurements are in-line with other tetrahedral complexes in the {NiNO} classification. In contrast to the established stability of this metal-nitrosyl class, the Ni-NO bond of is labile and release of NO from this unit was quantified by trapping the NO with a Co-porphyrin (70-80% yield). In the process, the Ni ends up coordinated by two -nitrosaminobenzenethiolato ligands to result in the structurally characterized -(EtN)[Ni(Ph-NO--CF)] (), likely by a disproportionation mechanism. The isolation and characterization of and suggest that: (i) the strongly donating thiolates dominate the electronic structure of Ni-nitrosyls that result in less covalent Ni-NO bonds, and (ii) superoxide undergoes disproportionation an outer-sphere mechanism in NiSOD as complexes in the {NiNO} state have yet to be isolated.