Reduction Rate of 1‑Phenyl Phospholane 1‑Oxide Enhanced by Silanol Byproducts: Comprehensive DFT Study and Kinetic Modeling Linked to Reagent Design

Important
stoichiometric transformations like Wittig and Appel
reactions have been implemented in a catalytic fashion in the past
decade. The phosphine oxide generated in situ can be reintroduced
as phosphine into the catalytic cycle using mild and selective silane
reagents (redox-driven catalysis). While the field of experimental
investigation has been fully expanding in the past decade, theoretical
studies are still sparse. In this present work, density functional
theory (DFT) has been used to characterize the free energy surfaces
of the reduction of 1‑phenyl phospholane 1‑oxide with
four different silanes. Found stationary points have been studied
in-depth to highlight mechanistic peculiarities, like the effect of
substituents at the silicon center and the parallel and competitive
reactivity between the precursor silanes and their semioxidized byproducts.
Calculated thermodynamic parameters in combination with “real”
values for concentrations have been used in the formulation of rate
equations for simple bimolecular and monomolecular steps of the mechanism.
The deterministic integration concentrations versus time of such rate
equations led to a realistic description of the systems under study
and paved the way to strategic and rational design of new silanes
with increased reactivity.