Trioctylphosphine selenide (TOPSe) is an organophosphorus compound with the formula SeP(C8H17)3.

[1] TOPSe is a white, air-stable solid that is soluble in organic solvents.

The molecule features a tetrahedral phosphorus center.

[2] As a solution with trioctylphosphine oxide, TOPSe reacts with dimethylcadmium to give cadmium selenide.

The mechanism is proposed to proceed in two steps, beginning with the formation of cadmium metal followed by its oxidation with the TOPSe.