phosphine

Phosphine (PH3) is the simplest phosphorus hydride and a colorless, highly flammable gas with a characteristic odor. It adopts a pyramidal molecular geometry, with phosphorus bearing a lone pair and three P–H bonds. The compound is a gas at room temperature, with a boiling point around −87.7°C, and is moderately soluble in water.

Phosphine is produced industrially by the reduction of phosphorus halides with hydrogen or metals, and it can also be generated in situ in fumigation or other processes. It behaves as a weak base and acts as a neutral two-electron donor ligand in coordination chemistry, forming a variety of metal complexes and serving as a precursor to many organophosphorus compounds.

Applications of phosphine and its derivatives are dominated by their role as ligands in homogeneous catalysis. Organophosphines, including simple PH3 derivatives and more complex PR3 compounds, are widely used to tune the activity and selectivity of metal catalysts employed in hydrogenation, hydroformylation, cross‑coupling, and related transformations.

Safety and handling are critical concerns. PH3 is highly toxic, with adverse effects on respiration; odor is not a reliable warning at low exposures. It is extremely flammable and can form explosive mixtures with air. Storage and use require robust precautions, including handling under inert atmospheres and in appropriate gas containment systems to exclude air and moisture.