Hydrophosphination

Hydrophosphination is a chemical transformation in which a P–H bond adds across a carbon–carbon multiple bond to form a new carbon–phosphorus bond. The reaction converts alkenes or alkynes into organophosphorus compounds bearing a phosphine or phosphide fragment. In its most common form, hydrophosphination of an alkene with a primary or secondary phosphine adds hydrogen to one carbon and a phosphine substituent to the other, yielding an alkyl phosphine. Hydrophosphination of alkynes furnishes vinyl phosphines after addition of H and PR2 across the triple bond.

Catalysis and mechanisms: The reaction can proceed via metal-catalyzed or radical pathways. A broad range of transition metals—nickel, palladium, copper, iron, and ruthenium—have supported hydrophosphination, often under light irradiation to promote radical processes. Organocatalytic and main-group approaches have also been reported. Mechanistic pictures include insertion of a metal–phosphido or hydride species into the unsaturated substrate or radical addition of a phosphinyl radical followed by hydrogen atom transfer. The outcome with respect to regio- and stereochemistry depends on the substrate and the catalyst, enabling anti-Markovnikov or Markovnikov products and, for alkynes, vinyl phosphines with defined geometry in some systems.

Scope and applications: Hydrophosphination provides a practical route to a broad set of organophosphorus compounds, including primary, secondary, and tertiary phosphines, ligands for homogeneous catalysis, intermediates for pharmaceuticals, and sites for further functionalization in polymer chemistry. The method has expanded with visible-light photocatalysis and with earth-abundant metals, enhancing functional-group tolerance and selectivity.

History: The reaction was explored in the mid-20th century and has gained renewed attention in recent decades with new catalytic strategies.

See also: hydrofunctionalization; P–H activation.