Organophosphines

Organophosphines are a class of organophosphorus compounds characterized by carbon–phosphorus bonds. They include primary, secondary, and tertiary phosphines with the general formula PRn, most commonly PR3 for tertiary phosphines. These compounds are typically colorless liquids or solids. Many are air- and moisture-sensitive and some are pyrophoric; they can be toxic and malodorous.

The phosphorus center bears a lone pair and can act as a soft, strong σ-donor ligand in metal complexes. Substituent choice on the phosphorus atom tunes electronic and steric properties, allowing a wide range of ligands from small and hard to very bulky and soft. They are widely used as ligands in homogeneous catalysis and coordination chemistry.

Synthesis methods: organophosphines are most commonly prepared by substitution of phosphorus trichloride or related chlorophosphines with organometallic reagents (such as Grignard reagents or organolithiums), giving PR3 after workup. They can also be prepared by reduction of phosphine oxides or by other multi-step routes from primary precursors.

Reactivity and applications: due to their strong σ-donor ability, organophosphines form stable complexes with transition metals and act as key ligands in catalysis. They enable hydroformylation and hydrogenation with rhodium or cobalt catalysts, cross-coupling reactions with palladium or nickel catalysts, and enantioselective transformations when employed as chiral ligands (for example BINAP, dppe derivatives). Simple phosphines like PPh3 remain widely used, while bulky and bidentate ligands offer fine control of selectivity.

Safety: many organophosphines are air-sensitive and some are toxic or flammable; handling typically requires inert atmosphere techniques.