[IL]2[PdCl4] complexes (IL = imidazolium cation) as efficient catalysts for Suzuki–Miyaura cross-coupling of aryl bromides and aryl chlorides
•Excellent catalytic activity of [IL]2[PdCl4] complexes in Suzuki–Miyaura reaction.•Efficient cross-coupling of aryl bromides and aryl chlorides with phenylboronic acid.•Positive effect of methyl substituent at the C2 carbon of imidazolium cation (IL).•TEM identification of Pd(0) nanoparticles in the reaction mixture.•Pd(0) nanoparticles act as a source of catalytically active soluble palladium species.
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 °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-dimethyl-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 °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.
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Journal: Applied Catalysis A: General - Volume 466, 10 September 2013, Pages 216–223