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