Understanding alkali-metal driven hydrophosphorylation: mechanism and challenges in the Pudovik reaction

Abstract

The addition of H–P(V) bonds of phosphane oxides across alkynes (hydrophosphorylation reaction) presents an effective synthetic strategy to generate alkenylphosphane oxides. This reaction requires a strong P-nucleophile, such as phosphinite, which can be generated by the reaction of a phosphane oxide with alkali metal amides, such as hexamethyldisilazanides (M-HMDS). Hydrophosphorylation exemplifies an important synthetic reaction facilitated by s-block metal bases. Extensive experimental studies have demonstrated the crucial impact of both the alkali cation and the P-bound substituent on reaction rates, product distribution, and the regio- and stereoselectivity of phosphane oxide addition. This study aims to provide a comprehensive mechanistic interpretation of the alkali metal-catalysed hydrophosphorylation reactions, employing density functional theory (DFT) calculations to clarify experimental findings. Our analysis focuses on two critical stages: 1) formation of the active alkali metal phosphinite species through the metalation–deprotonation of phosphane oxide by M-HMDS, and 2) the subsequent H–P addition onto the alkyne. Additionally, the study addresses side processes that may deactivate the active species by lowering its concentration in solution, potentially impacting the overall reaction efficiency. Computational modelling of reaction mechanisms involving s-block metal cations has been less explored than those with transition metal complexes and faces solvation and speciation as major challenges. This article also discusses the computational requirements necessary for accurate chemical modelling of these systems, as well as the limitations inherent in the employed approach.