Diphenylphosphine, also known as diphenylphosphane, is an organophosphorus compound with the formula (C6H5)2PH. This foul-smelling, colorless liquid is easily oxidized in air. It is a precursor to organophosphorus ligands for use as catalysts.
Diphenylphosphine can be prepared from triphenylphosphine by reduction to lithium diphenylphosphide, which can be protonated to give the title compound:
In the laboratory, diphenylphosphine is a common intermediate. It can be deprotonated to give diphenylphosphide derivatives:
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.
Compared to tertiary phosphines, diphenylphosphine is weakly basic. The pKa of the protonated derivative is 0.03:
Diphenylphosphine readily oxidizes.
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.