Lewis Acid Assisted Nitrate Reduction with Biomimetic Molybdenum Oxotransferase Complex

The reduction of nitrate (NO₃^-) to nitrite (NO₂^-) is of significant biological and environmental importance. While Mo^IV(O) and Mo^VI(O)₂ complexes that mimic the active site structure of nitrate reducing enzymes are prevalent, few of these model complexes can reduce nitrate to nitrite through oxygen atom transfer (OAT) chemistry. We present a novel strategy to induce nitrate reduction chemistry of a previously known catalyst Mo^IV(O)(SN)₂ (2), where SN = bis(4- tert-butylphenyl)-2-pyridylmethanethiolate, that is otherwise incapable of achieving OAT with nitrate. Addition of nitrate with the Lewis acid Sc(OTf)₃ (OTf = trifluoromethanesulfonate) to 2 results in an immediate and clean conversion of 2 to Mo^VI(O)₂(SN)₂ (1). The Lewis acid additive further reacts with the OAT product, nitrite, to form N₂O and O₂. This work highlights the ability of Sc³⁺ additives to expand the reactivity scope of an existing Mo^IV(O) complex together with which Sc³⁺ can convert nitrate to stable gaseous molecules.