Diphenylphosphine oxide

Diphenylphosphine oxide is an organophosphorus compound with the formula (C6H5)2P(O)H. It is a white solid that soluble in polar organic solvents.

Synthesis
Diphenylphosphine oxide can be prepared by the reaction of phosphonic esters, such as diethylphosphite, with Grignard reagents followed by acid workup:
 * (C2H5O)2P(O)H +  3C6H5MgBr  →  (C6H5)2P(O)MgBr  +  C2H5OMgBr
 * (C6H5)2P(O)MgBr +  HCl →  (C6H5)2P(O)H  + MgBrCl

Alternatively, it may be prepared by the partial hydrolysis of chlorodiphenylphosphine or diphenylphosphine.

Reactions
Diphenylphosphine oxide exists in equilibrium with its minor tautomer diphenylphosphinous acid, ((C6H5)2POH:
 * (C6H5)2P(O)H <->  (C6H5)2POH

Diphenylphosphine oxide is used in Buchwald-Hartwig coupling reactions to introduce diphenylphosphino substituents.

Thionyl chloride converts diphenylphosphine oxide to chlorodiphenylphosphine.

Organophosphinous acids are deoxygenated with DIBAH. The resulting secondary phosphines are precursors to phosphine ligands.