Pd-Catalyzed Arylation of Phosphines: Reversibility and Ligand Exchange Issues

Abstract

Our studies on the fate of the phosphine co-catalyst in the Heck arylation reaction have revealed that the quaternary tetraarylphosphonium cations which are formed from triphenylphosphine and aryl iodide under the reaction conditions undergo an aryl exchange process with the aid of the palladium catalyst Independent exchange studies as well as model Heck arylation reactions carried out in the presence of stoichiometric amounts of tetraphenylphosphonium iodide demonstrated clearly that the Pd-catalyzed aryl exchange between aryl iodide and tetraarylphosphonium cation is a facile process which can effectively compete with the Heck arylation The observed exchange process is reversible and involves triarylphosphines as discrete intermediates.