Origin of Reactivity Difference between Phosphines and Phosphinites in Ru-Catalyzed Phosphorus-Directed sp2C–H Borylation: Mechanistic Study and Improvement of Reaction Conditions

The reaction mechanism of Ru-catalyzed phosphorus-directed ortho sp2C–H borylation of triarylphosphines and aryl phosphinites was investigated. Competition experiments and time course analyses clarified the existence of an induction period when using [RuCl2(p-cymene)]2 as a catalyst, which was attributed to substitution of the p-cymene ligand by phosphorus compounds to generate a reactive species. These studies have reasonably explained the origin of the reactivity difference between triarylphosphines and aryl phosphinites. Dramatic improvement of reaction conditions for aryl phosphinites was achieved by employing RuCl2(dmso)4 as a new catalyst based on the mechanistic insights, realizing borylation of aryl phosphinites at room temperature. Mechanistic investigations on the [RuCl2(p-cymene)]2-catalyzed phosphorus-directed ortho sp2C–H borylation clarified the reactivity difference between triarylphosphines and aryl phosphinites as substrates and the existence of an induction period to generate a p-cymene-free active Ru species. Based on these results, improvement of reaction conditions for aryl phosphinites was achieved by employing RuCl2(dmso)4 as a new catalyst.