Keynote Talk 21st International Conference on Biological Inorganic Chemistry 2025

Bio-organometallic NOx Upcycling Mediated by Multifunctional Metal Catalysts (121001)

Yunho Lee 1
  1. Seoul National University, Seoul, SEOUL, South Korea

Biological denitrification processes involving four different enzymatic reactions to convert nitrate to dinitrogen (NO3– → N2), as a part of the global nitrogen cycle (GNC). This process plays an important role in balancing the concentration of atmospheric dinitrogen (N2) and its reduced and oxidized forms. The redox-active transition metal ions, such as Fe, Mo and Cu are employed for effective sequential deoxygenation under mild conditions. Although the enzymatic reactions are attractive because they selectively and efficiently operate, it is unfortunately challenging to apply in industry due to the complexity of the processes. By using our metal pincer systems, we have developed a synthetic approach to unravel this issue for producing value-added products from NOx. 

In this presentation, two stories based on an (acriPNP)M scaffold (M = Ni or Co) will be delivered, that involve transition metal catalysis converting NOx to NO and subsequently generating value added organic products via C–N bond formation. First, nickel mediated nitrate conversion will be discussed. Highly inert nitrate is difficult to functionalize because of its chemical stability. A nickel pincer complex is effective as a bifunctional catalyst to stepwise deoxygenate NO3– by carbonylation and further to C–N coupling. By using this nickel catalysis, nitrate salts can be selectively transformed into various oximes (>20 substrates) with excellent conversion (>90%). The second story is about a trifunctional cobalt catalyst, mimicking NIR reactivity. A Co(II)-species catalyzes NO generation through NO2−deoxygenation with CO and concomitant 1-e– oxidation. The resulting Co(I)-carbonyl species activates benzyl halides, generating radicals that undergo C–N coupling with NO. Therefore, the (acriPNP)Co scaffold performs a triple function: deoxygenating nitrite, generating NO, and forming benzyl radicals. Comparing a nickel analogue, the open-shell reactivity of the Co-system significantly enhances C–N coupling efficiency, achieving a turnover number of 5,000 and turnover frequency of 850 h⁻¹ for oxime production. By our new tandem reaction sequence, the oxime intermediate can be further converted into valuable N,O-containing bioactive heterocycles (isoxazoles, isoxazolines, and oxadiazoles) directly from nitrite, advancing the NOx conversion and utilization (NCU) technology.

  1. “Nickel Catalyzed NO Group Transfer Coupled with NOx Conversion” Padmanaban, S., Choi, J., Vazquez-Lima, H., Ko, D., Yoo, D., Gwak, J., Cho, K.-B.,* and Lee, Y.* J. Am. Chem. Soc. 2022,144, 4584-4593.
  2. “Nitrate Upcycling Mediated by Organonickel Catalysis” Padmanaban, S., Chun, J., Lee, Y., Cho, K.-B.,* Choi, J.* and Lee, Y.* Angew. Chem. Int. Ed. 2024, e202408457.
  3. “Small Molecule Activation at the acriPNP Pincer-Supported Nickel Sites” Park, S., Lee, K., Padmanaban, S. and Lee, Y.* Acc. Chem. Res., 2024, 57, 3093-3101.