Properties of Free Phosphines

Phosphines are more susceptible to oxidation than amines because P(V) is a stable oxidation state. Thus, some phosphines are air sensitive and must be handled under an inert atmosphere. Many alkylphosphines are air sensitive, but arylphosphines and phosphites, which are less electron rich than alkylphosphines, are less sensitive or are indefinitely stable to air. Also, more sterically hindered alkylphosphines are less air sensitive than less-hindered alkylphosphines.  

Barrier to Interconversion and one of the first ligands for asymmetric hydrogenation. 

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