Reduction of Phosphine Oxide by Using Chlorination Reagents and Dihydrogen: DFT Mechanistic Insights

Extensive DFT calculations provide detailed mechanistic insights into the metal‐free reduction of phosphine oxide Ph 3 P=O by using chlorination reagents O=CClX (X=COCl, Cl, OCCl 3 and Ph) and H 2 . Fast electrophilic attack to the P=O group oxygen atom is favored by exergonic CO 2 release to form phosphonium Ph 3 PCl + and chloride Cl − , which may slowly cleave H 2 by an unstable HPh 3 PCl complex yielding Ph 3 PH + and Cl − ions in solution. Moderate heating is required to accelerate the slow H 2 ‐activation step and to eliminate HCl to form phosphine Ph 3 P instead of Ph 3 PH + Cl − salt as the desired product. Though partially quenched by Ph 3 P (and reactant Ph 3 P=O if present), borane B(2,6‐F 2 C 6 H 3 ) 3 can be still combined with Cl − and Ph 3 P as reactive frustrated Lewis pair (FLP) catalysts.