An increase in fertilization since the dawn of the Industrial Revolution has caused extensive eutrophication leading to aquatic dead zones, which can be attributed to the large amounts of NO3- that are washed downstream before being absorbed by crop roots. Thus, the reduction of NO3-, and subsequently NO2-, is a critical yet unresolved problem that is necessary to restore balance to the natural nitrogen cycle. While some success for the reduction of NO3- and NO2- has been seen in hetereogenous systems, we target less expensive and more efficient homogenous catalysis. The use of a redox active pincer ligand, bis-tetrazinyl-pyridine (btzp), allows for the storage of both protons and electrons that can be delivered to high oxidation state nitrogen oxyanions. Functionalizing btzp into H4btzp yields a pre-reduced ligand that can provide four electrons and four protons. When bound to iron, H4btzp spontaneously reduces NO2-, to give a dinitrosyl iron complex, Fe(NO)2btzp. In the case of ZnCl2H4btzp, we see similar reactivity to give a product with a formula of Zn(N2O2)btzp. Attempts at further reduction of the nitrosyl ligands, as well as the nature of the reduced NO2- product with zinc will be described. Nitrate reduction does not proceed spontaneously, and attempts to use both chemical reductants and oxygen atom transfer reagents to deoxygenate nitrate bound to both iron and zinc is discussed.

Reduction of high oxidation state nitrogen oxyanions using a pre-reduced redox active pincer ligand

256th National Meeting (2018)

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