[IL]2[PdCl4] complexes (IL = imidazolium cation) as efficient catalysts for Suzuki-Miyaura cross-coupling of aryl bromides and aryl chlorides

Palladium complexes of the type [IL](2)[PdCl4] (IL = imidazolium cation) were found to be very active catalysts for the Suzuki-Miyaura reaction of 2-bromotoluene with phenylboronic acid carried out in 2-propanol or 2-propanol/water at 40 degrees C using normal heating or microwaves as a heating source. In 2-propanol, the highest yields (89% and 85%) were obtained for [dmiop](2)[PdCl4] and [dmdim][PdCl4] (dmiop = 1,2-dimethy1-3-propoxymethyl imidazolium cation, dmdim =3,3'-[1,7-(2,6-dioxaheptane)]bis(1,2-dimethylimidazolium) cation) containing cations substituted at the C2 carbon with a methyl group. In the presence of water, all [IL](2)[PdCl4] complexes produced ca. 90% of 2-methylbiphenyl. Very good results were also obtained in the Suzuki-Miyaura reaction of different aryl bromides and chlorides. For example, the conversion of 2-chlorotoluene was 71% at 70 degrees C. During the catalytic reaction, the formation of Pd(0) nanoparticles was evidenced by TEM. Mechanistic studies, including Hg(0) tests, showed that Pd(0) nanoparticles acted as a source of catalytically active soluble palladium species. (C) 2013 Elsevier B.V. All rights reserved.