Trioctylphosphine is an organophosphorus compound with the formula P(C<sub>8</sub>H<sub>17</sub>)<sub>3</sub> sometimes abbreviated TOP. It is usually encountered as a syrup. The compound is colorless.
Trioctylphosphine reacts with oxygen to form trioctylphosphine oxide. For this reason it is usually handled with air-free techniques.
TOP reacts with elemental selenium to give trioctylphosphine selenide (TOPSe), which is a reagent for the preparation of cadmium selenide and related semiconductors.