Formation of Red Elemental Selenium from Seleniferous Oxyanions: Deoxygenation by a Homogeneous Iron Catalyst

Seleniferous oxyanions are groundwater contaminants from both anthropogenic and natural sources, while pure amorphous selenium nanoparticles have a variety of industrial applications. Biology can achieve the multicomponent 6 e^-/8 H⁺ reduction of selenate to amorphous selenium using multiple metalloenzymes, like selenate and selenite reductase. Inspired by biology, we developed a new homogeneous system that can generate pure elemental selenium with no caustic waste. The stoichiometric reductions of selenate, selenite, and selenium dioxide with an iron(II) complex produced an iron(III)-oxo and red elemental selenium, the latter of which has been characterized by a variety of spectroscopic techniques. The catalytic reduction of SeO₄^2- and SeO₃^2- directly to amorphous Se and isolated as Se=PPh₃ is reported with a turnover number of 12 and 7, respectively.