Woollins' reagent

Other names: 2,4-Diphenyl-1,3,2λ⁵,4λ⁵-diselenadiphosphetane-2,4-diselone

C₁₂H₁₀P₂Se₄

7/50 common

Woollins’ reagent is a selenium-based analogue of Lawesson’s reagent, used for the selenation of C=O carbonyl moieties to form C=Se selenocarbonyl derivatives. Like its sulfur counterpart, it features a four-membered phosphorus-chalcogen heterocycle that decomposes under reaction conditions to generate highly reactive phosphorus selenide species. First reported by John Woollins in the 1990s, it has since become a valuable tool in organoselenium chemistry. Woollins’ reagent forms strikingly deep red crystals, making it visually distinctive. However, this beauty is accompanied by an infamously vile odor, as the compound decays in air to unbearably pungent hydrogen selenide ("like rotting horseradish").