Diphenylphosphine

Synthesis

Diphenylphosphine can be prepared from triphenylphosphine by reduction to lithium diphenylphosphide, which can be protonated to give the title compound: :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 (Ph2PCH2CH2PPh2) and BINAP via their respective bistriflate derivatives. Both the (R)- and (S)-enantiomers, as well as the racemate, are commercially available. One of the wide applications include chemoselective hydrogenation, where BINAP is conjugated to rhodium.

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.

References

References

1. V. D. Bianco. (1976). "Inorganic Syntheses".
2. Piotrowski, D. W.. (2001). "Diphenylphosphine". John Wiley & Sons.
3. Cai, Dongwei. (1999). "(''R'')-(+)- and (''S'')-(−)-2,2′-bis(diphenylphosphino)-1,1′-binapthyl (BINAP)".
4. C. A. Streuli, "Determination of Basicity of Substituted Phosphines by Nonaqueous Titrimetry", Analytical Chemistry 1960, volume 32, pages 985-987.{{doi. 10.1021/ac60164a027
5. Svara, J.. "Phosphorus Compounds, Organic".