Fosfens

Fosfens, known in English as phosphines, are a class of organophosphorus compounds characterized by a phosphorus atom bonded to three substituents and bearing a lone pair. The general formula is PR3, where R can be hydrogen or alkyl or aryl groups. Subclasses include primary phosphines (RPH2), secondary phosphines (R2PH), and tertiary phosphines (PR3). The simplest member is phosphine, PH3.

Phosphines vary widely in volatility, odor, and air sensitivity. Many tertiary phosphines are colorless liquids or solids, while primary and secondary phosphines are often volatile and malodorous. They are typically air- and moisture-sensitive and can be oxidized to phosphine oxides (OPR3). The electronic and steric properties of phosphines can be tuned by changing the nature of the R groups, affecting their behavior as ligands and reagents.

Phosphines are especially important as ligands in coordination chemistry and homogeneous catalysis. They are strong sigma-donor ligands and can be tuned to modify the reactivity and selectivity of metal centers, enabling a wide range of transformations such as hydrogenation, hydroformylation, cross-coupling, and various polymerization processes. Common examples include triphenylphosphine (PPh3), tri-tert-butylphosphine, and trimethylphosphine (PMe3).

Preparation and handling of phosphines often require air-free techniques, as many are sensitive to oxidation and moisture. They can be toxic and flammable; exposure may cause irritation or other health effects, and proper laboratory precautions are necessary.

See also: phosphine oxide; organophosphorus chemistry.