Neues aus der Chemie der niederen Schwefeloxyde

Reduction of Sulfur Dioxide to Sulfur Monoxide by Ferrous Porphyrin

The reduction of SO₂ to fixed forms of sulfur can address the growing concerns regarding its detrimental effect on health and the environment as well as enable its valorization into valuable chemicals. The naturally occurring heme enzyme sulfite reductase (SiR) is known to reduce SO₂ to H₂ S and is an integral part of the global sulfur cycle. However, its action has not yet been mimicked in artificial systems outside of the protein matrix even after several decades of structural elucidation of the enzyme. While the coordination of SO₂ to transition metals is documented, its reduction using molecular catalysts has remained elusive. Herein reduction of SO₂ by iron(II) tetraphenylporphyrin is demonstrated. A combination of spectroscopic data backed up by theoretical calculations indicate that Fe^II TPP reduces SO₂ by 2e^- /2H⁺ to form an intermediate [Fe^III -SO]⁺ species, also proposed for SiR, which releases SO. The SO obtained from the chemical reduction of SO₂ could be evidenced in the form of a cheletropic adduct of butadiene resulting in an organic sulfoxide.

Crystalline, room-temperature stable phosphine–SO2 adducts: generation of sulfur monoxide from sulfur dioxide

Particularly basic phosphines form isolable Lewis base adducts with SO₂ that readily release SO at room temperature driven by the formation of the corresponding phosphine oxides.