Nitric oxide (NO) plays a key role in biological systems as a cellular signaling molecule involved in many physiological and pathological processes. Nitrite (NO2-) represents a tightly regulated and important circulating reservoir for NO in biological systems. Encouraged by the production of NO from nitrite by the enzyme copper nitrite reductase, characterization of copper intermediates in enzymes and other catalysts that convert nitrite to NO may uncover new mechanisms available to biology. Here, we seek to understand factors responsible for the reversible cleavage of the O-NO bond of nitrite by employing model complexes with two different ligand scaffolds. Use of β-diketiminate ligands allows for the synthesis and interconversion of copper(I) and copper(II) nitrite complexes {[Cu]-NO2}- and [Cu](κ2-O2N), respectively. We find that the addition of reductants such as PPh3 to copper(II) complexes [Cu](κ2-O2N) triggers loss of NO with reduction to copper(I) whereas the nitrite ligand in the copper(I) complex {[Cu]-NO2}- is simply displaced by PPh3. These studies provide new insights into the oxidation state and coordination environment dependence of transformations involved in nitrite/nitric oxide chemistry at copper. Additionally, we examine the use of tris(pyrazolyl)borate ligands that possess a pendant arm capable of engaging in H-bonding interactions with ligands within the copper coordination sphere to outline the role of H+ ions in the reversible cleavage of the O-NO bond.

Nitrite to nitric oxide conversion at copper(I) and copper(II) sites

254th National Meeting (2017)

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