P(O)H to P–OH Tautomerism: A Theoretical and Experimental Study

Phosphinylidene compounds R1R2P­(O)H are important functionalities in organophosphorus chemistry and display prototropic tautomerism. Quantifying the tautomerization rate is paramount to understanding these compounds’ tautomerization behavior, which may impact their reactivities in various reactions. We report a combined theoretical and experimental study of the initial tautomerization rate of a range of phosphinylidene compounds. Initial tautomerization rates are found to decrease in the order H3PO2 > Ph2P­(O)H > (PhO)2P­(O)H > PhP­(O) (OAlk)­H > AlkP­(O)­(OAlk)H ≈ (AlkO)2P­(O)­H, where “Alk” denotes an alkyl substituent. The combination of computational investigations with experimental validation establishes a quantitative measure for the reactivity of various phosphorus compounds, as well as an accurate predictive tool.