Phosphine-borane

In chemistry, phosphine-boranes are organophosphorus compounds with the formula R_3−nH_nPBH₃. They are Lewis acid-Lewis base adducts derived from organophosphines (PR_3−nH_n) and borane (BH₃). They are generally colorless or white solids. Since these adducts are air-stable, they represent a protected form of the parent organophosphine.^[1][2]

Structure of Me₃PBH₃, a phosphine-borane.

Formation and decomplexation

Typically phosphine-boranes are produced by treating the parent phosphine with a source of borane:

PR_3−nH_n + BH₃ → R_3−nH_nPBH₃

Because borane solutions are expensive or dangerous, the borane is often generated in situ, e.g., by oxidation of borohydride with iodine.^[3]

Deprotection to liberate the phosphine is often achieved by treatment with a tertiary amine:^[2]

R_3−nH_nPBH₃ + R'₃N → R'₃NBH₃ + R_3−nH_nP

See also

• Frustrated Lewis pair, where the borane is often tris(pentafluorophenyl)borane
• Ammonia borane, related to phosphine-borane but with ammonia or amines in place of organophosphines