Diphenylphosphine

Synthesis

Diphenylphosphine can be prepared cheaply from triphenylphosphine.

PPh₃ + 2 Li → LiPPh₂ + LiPh LiPPh₂ + H₂O → Ph₂PH + LiOH

Uses and reactions

In the laboratory, diphenylphosphine is a common intermediate. It can be deprotonated to give diphenylphosphide derivatives:

Ph₂PH + ⁿBuLi → Ph₂PLi + ⁿBuH

The preparation of phosphine ligands, Wittig-Horner reagents, and phosphonium salts are commonly accomplished by alkylating diphenylphosphine. The hydrogen atom connected to phosphorus undergoes Michael-like addition to activated alkenes, providing products with which to produce phosphine ligands such as 1,2-bis(diphenylphosphino)ethane (Ph₂PC₂H₄PPh₂). Diphenylphosphine and especially diphenylphosphide derivatives are nucleophiles, so they add to carbon – heteroatom double bonds. For example, in the presence of concentrated hydrochloric acid at 100 °C, diphenylphosphine adds to the carbon atom in benzaldehyde to give (phenyl-(phenylmethyl)phosphoryl)benzene.

Ph₂PH + PhCHO → Ph₂P(O)CH₂Ph

Compared to tertiary phosphines, diphenylphosphine is weakly basic. The pKa of the protonated derivative is 0.03:

Ph₂PH₂⁺ ⇌ Ph₂PH + H⁺

Handling properties

Diphenylphosphine readily oxidizes.

Ph₂PH + O₂ → Ph₂P(O)OH

An intermediate in this oxidation is diphenylphosphine oxide. The use of the diphenylphosphine–borane complex, Ph₂PH•BH₃ avoids the problem of phosphine oxidation by protecting the phosphine from oxidation and is available through chemical vendors.