PPh3

Triphenylphosphine, abbreviated PPh3, is an organophosphorus compound with the formula C18H15P. It is a tertiary phosphine that functions as a common ligand in homogeneous catalysis. As a two-electron σ-donor (L-type) through the phosphorus atom, PPh3 binds to many transition metals, stabilizing low-oxidation-state centers and shaping reactivity.

Physically, PPh3 is a solid at room temperature, typically colorless to pale yellow, with a distinctive odor. It is soluble in nonpolar organic solvents such as benzene, toluene, and diethyl ether, and is less soluble in water. The solid is relatively air-stable, but the compound can slowly oxidize in air to triphenylphosphine oxide (OPPh3), especially in solution or upon exposure to light; solutions are frequently prepared under inert atmosphere.

In coordination chemistry, PPh3 is one of the most common monodentate phosphine ligands. It forms well-known complexes such as Pd(PPh3)4, RhCl(PPh3)3, and related species. The ligand’s electronic donation and moderate steric demand influence catalytic activity in reactions including hydrogenation, hydroformylation, and cross-coupling (Suzuki–Miyaura, Heck, Negishi). It can be displaced by substrate or stronger-binding ligands during catalytic cycles and is often used in excess or paired with other phosphines to tune selectivity.

Synthesis and availability: PPh3 is commercially available and widely used in laboratories. It can be prepared or purified from triphenylphosphine oxide via reduction routes; various industrial production routes exist.

Safety notes: PPh3 has relatively low acute toxicity but can be irritating; handle with appropriate precautions. Oxidation to OPPh3 reduces donor strength and is typically avoided in catalytic preparations.