Increasing attention has been paid to four-coordinate pentavalent organophosphorus compounds with a PSe group because of their wide applicability to a range of research fields.¹  The phosphorus atom of their PSe group could have three different substituents, which provide numerous substitution patterns. For example, phosphine selenides have three carbon-containing substituents on the phosphorus atom (P–C bonds). In general, they are synthesized from trivalent phosphines and elemental selenium. Treating phosphines 1 with selenium powder in benzene gave the corresponding phosphine selenides 2 in good yields (Scheme 8.1).² 

Phosphine selenides have been utilized for various purposes. For instance, tri(n-octyl)phosphine selenide provided the selenium atom to Cd oleate to synthesize CdSe quantum dots.^3,4  Likewise, the reaction of [Ni(1,5-COD)₂] with Et₃PSe gave a [Ni₂₃Se₁₂Cl₃(PEt₃)₁₀] cluster in which selenium atoms constructed the main cluster shell.⁵  Cocrystallization of triphenylphosphine selenide (3) with iodobenzenes (1,3-F₄DIB, IF₅B) revealed their unique intermolecular interactions (Scheme 8.2).