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Published on: April 10, 2018
Reductive and Oxidative Transformations of Nitrite at Nickel(II): Insights into the Generation, Electronic Structure,
Balakrishnan S Anju1, Neeraja R Nair1, Janavi Rajput2
1School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Thiruvananthapuram 695551, India.
Abstract:
The diverse redox transformations of nitrite (NO2 -) link key signaling molecules like nitric oxide (NO) and enable precise regulation of NO flux in physiology. This report employs structurally and spectroscopically characterized mononuclear [Ni]-NO x complexes to illustrate nitrogen-oxide redox chemistry, including conversions between nitrite, NO, and nitrate. Reduction of [(Me2PzQu)2NiII(nitrite)]-(ClO4) 1-Qu by p-methylthiophenol (MeArSH) leads to a {NiNO}10 species [(Me2PzQu)-Ni-(NO)-(ClO4)] 3-Qu through the intermediacy of HNO2 and MeArSNO. Interestingly, subtle modifications in the ligand properties distinctly influence the thiol-nitrite reactivity and the stability of the resulting {NiNO}10 species. Importantly, the crosstalk between H2S and nitrite at the nickel-(II) site also results in reductive nitrosylation to afford the {NiNO}10 species. Although the detection of transient HNO2 is challenging, this study uniquely employs a phosphine-mediated deoxygenation strategy to demonstrate intermediacy of HNO2 during thiol reactions of [(Me2PzQu)2MII(nitrite)]+ (M = Ni/Zn). In addition, NO and NO- ligand transfer reactivity of the {NiNO}10 core in 3-Qu have been evaluated. Using iodosylbenzene (PhIO) as a sacrificial O-atom donor, both 1-Qu and 3-Qu complexes have been shown to yield [NiII]-nitrate 2-Qu, thereby outlining a stepwise O-atom transfer (OAT) pathway for nitrosyl → nitrite → nitrate transformations. Taken together, these findings reveal reductive nitrosylation via nitrite-thiol/H2S crosstalk and demonstrate a stepwise OAT-dependent route for NO/nitrite oxidation using a common coordination motif.
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