Tetraalkylammonium salts as promoters for Suzuki-Miyaura reactions catalyzed by a palladium allyl complex containing a thioether-1,2,3-triazole ligand. Influence of the cation and anion of the ammonium salt on the catalytic activity

The novel cationic palladium–allyl complex [Pd(C3H5)(1-(2-(methylthio)ethyl)-4-phenyl-1H-1,2,3- triazole)](BF4) (2) is a precatalyst for the Suzuki–Miyaura reaction. Good turnover numbers are obtained in the reaction between different aryl bromides and phenylboronic acid in toluene with K2CO3 as the base. No reaction is instead observed with aryl chlorides due to catalyst decomposition to palladium black. Catalyst decomposition can be circumvented by adding tetraalkylammonium salts in the presence of which reasonably good reaction rates are obtained in the coupling of different aryl chlorides with phenylboronic acid. The beneficial effect of tetraalkylammonium salts is found to depend on the nature of the additive as well as the additive to substrate molar ratio. A systematic study allows to delineate the roles played by the cation and the anion of the promoter.