Nitrate and Perchlorate Reduction by a Dinuclear Mo(V) Complex

Nitrate (NO₃^-) and perchlorate (ClO₄^-) are persistent groundwater contaminants due to their high stability and solubility. Microorganisms reduce these anions using molybdenum-containing enzymes such as nitrate reductases and perchlorate reductases. Reported here is a bioinspired dinuclear Mo(V) catalyst, [Mo₂O₃(L^Br)₂(THF)₂] (<b>2</b>), where L^Br = 5-Bromo-2-hydroxybenzaldehyde thiosemicarbazone, and its reactivity with nitrate and perchlorate. Compound <b>2</b> was previously speculated to be an inactive byproduct formed when its monomeric Mo(VI) analog, [Mo^VIO₂(L^Br)(MeOH)] (<b>1</b>), catalyzes an oxygen atom transfer (OAT) between dimethyl sulfoxide (DMSO) and PPh₃. This work reports the synthesis, spectroscopic and crystallographic characterizations, and catalytic reactivity of <b>2</b>. Contrary to earlier expectations, <b>2</b> catalyzes OAT from DMSO to PPh₃, and also reduces nitrate and perchlorate, making it one of the few homogeneous molybdenum catalysts known to do so. With nitrate, <b>2</b> performs two OAT steps per NO₃^- to generate <b>1</b> and N₂O, likely via nitrite and nitroxy intermediates. With perchlorate, <b>2</b> catalyzes four OAT events per ClO₄^-, yielding Cl^- and <b>1</b>. The effect of Sc³⁺ as a cocatalyst was also investigated; it significantly enhances the rates for perchlorate reduction but has minimal impact on nitrate reduction.