Phosphines are an important class of organophosphorus compounds. They are often used as ligands in metal complex catalysis and they have become a popular reagent for organocatalysis. The methods most widely used for the synthesis of phosphines include the reaction of organometallic compounds with halophosphines, the reaction of metal phosphides with alkyl halides, the reduction of other phosphorus compounds and the hydrophosphination. Research in the past years has focused on the catalytic synthesis of phosphines. The asymmetric catalytic synthesis of chiral phosphines has only recently emerged and is under full development. Chiral phosphines are interesting ligands for the preparation of transition metal complex catalysts for asymmetric synthesis. Only a minor part of the chiral phosphines are chiral at the phosphorus atom (P-stereogenic).
A major drawback of phosphines is their highly oxidizable nature. They are easily converted to the corresponding phosphine oxide which makes the isolation difficult. To prevent losses during purification, the phosphines are sometimes deliberately transformed into the corresponding oxides (or sulfides). However, this requires an additional reduction step afterwards to get the phosphine back. Therefore phosphines are sometimes protected by generation of the corresponding phosphine– borane complex. The phosphine–borane complex is a stable intermediate toward the free phosphine. If necessary the boranato group can be removed by treatment with an excess of amine. However, not all phosphines are prone to oxidation and show good air-stability. This review will provide a general overview on phosphine synthesis over the last 10 to 15 years. Only reactions establishing a C–P bond will be discussed.
The full review article, Preparation of phosphines through C–P bond formation, is published online in Beilstein Journal of Organic Chemistry and is free to access.
Beilstein J. Org. Chem. 2014, 10, 1064–1096.