The Role of the Fluoro–Hydrido–Phosphorane Intermediate in Catalytic Hydrosilylation of Acetophenone: Computational Study

The fluorophosphonium cation [(C₆F₅)₃PF]⁺ (1) is used as a catalyst in many chemical transformations including the hydrosilylation of ketones. In these reactions the fluoro–hydrido–phosphorane (C₆F₅)₃PFH, which is formed upon a hydride abstraction by 1 from a hydrosilane, was proposed as the key intermediate. One of the most important features attributed to (C₆F₅)₃PFH in the catalytic hydrosilylation of ketones is its ability to transfer the hydride to an electrophile. However, (C₆F₅)₃FPH was not observed experimentally and its properties and in particular its hydride-donating ability was not studied in detail. In this work the mode of formation of (C₆F₅)₃FPH, its properties and its interactions with substrates in the catalytic hydrosilylation of acetophenone were investigated by density functional theory (DFT), and possible routes of this catalytic reaction were studied. Calculations show that (C₆F₅)₃PFH can act both as a fluoride and hydride donor, and that these processes can exist in thermodynamic equilibrium. However, only the donation of the hydride results in intermediates that allow the catalytic cycle to proceed.