Reductive and Oxidative Transformations of Nitrite at Nickel(II): Insights into the Generation, Electronic Structure, and Reactivity of {NiNO} 10

The diverse redox transformations of nitrite (NO 2 - ) link key signaling molecules like nitric oxide (NO) and enable precise regulation of NO flux in physiology. This report employs structurally-characterized mononuclear [Ni]-NO x complexes to illustrate nitrogen-oxide redox chemistry, including conversions between nitrite, NO, and nitrate. Reduction of [( Me 2 PzQu ) 2 Ni II (nitrite)](ClO 4 ) 1-Qu by p-methylthiophenol ( Me ArSH) leads to a {NiNO} 10 species [( Me 2 PzQu )Ni(NO)(ClO 4 )] 3-Qu through the intermediacy of HNO 2 and Me ArSNO. 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 H 2 S and nitrite at nickel(II) site results in reductive nitrosylation to afford the {NiNO} 10 species. This study uniquely employs a phosphine-mediated deoxygenation strategy to demonstrate intermediacy of HNO 2 during thiol reactions of [( Me 2 PzQu ) 2 M II (nitrite)] + (M = Ni/Zn). In addition, NO and NOligand 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 yield [Ni II ]-nitrate 2-Qu , thereby outlining a stepwise O-atom transfers (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 relevant to the terminal steps of nitrification.