Synthesis, purification, and characterization of phosphine oxides and their hydrogen peroxide adducts

Reactions of the tertiary phosphines R3P (R= Me, Bu, Oct, Cy, Ph) with 35% aqueous H2O2 gives the corresponding oxides as the H2O2 adducts R3P=O center dot(H2O2)(x) (x = 0.5-1.0). Air oxidation leads to a mixture of products due to the insertion of oxygen into one or more P-C bonds. P-31 NMR spectroscopy in solution and in the solid state, as well as IR spectroscopy reveal distinct features of the phosphine oxides as compared to their H2O2 adducts. The single crystal X-ray analyses of Bu3P=O and [Cy3P=O center dot(H2O2)](2) show a P=O stacking motif for the phosphine oxide and a cyclic structure, in which the six oxygen atoms exhibit a chair conformation for the dimeric H2O2 adduct. Different methods for the decomposition of the bound H2O2 and the removal of the ensuing strongly adsorbed H2O are evaluated. Treating R3P=O center dot(H2O2)(x) with molecular sieves destroys the bound H2O2 safely under mild conditions (room temperature, toluene) within one hour and quantitatively removes the adsorbed H2O from the hygroscopic phosphine oxides within four hours. At 60 degrees C the entire decomposition/drying process is complete within one hour.