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

The particularly basic phosphines 1a-c readily form isolable, zwitterionic Lewis base adducts with SO2 that were fully characterized including by X-ray diffraction studies. Computational and reactivity studies show that these adducts readily release SO at room temperature driven by the formation of the corresponding phosphine oxides.