GREEN CONDITIONS FOR THE SUZUKI REACTIONS BY USING MICROWAVE IRRADIATION AND MODIFIED HALLOYSITE/Pd CATALYST

Abstract

Halloysite nanotube (HNT) is an emerging biocompatible material with appealing perspective for technological applications, such as in catalysis1 and in pharmaceutical research.2 Halloysite is a double-layered aluminosilicate mineral that has a predominantly hollow tubular structure. The functionalization of HNTs is a good strategy to introduce an organic moiety onto the external surface and, therefore, to obtain innovative catalyst supports.3 We have modified the external surface of halloysite nanotube with octylimidazolium moieties (HNT-IL) by microwave irradiation in solvent-free conditions and we have have employed this material as support catalyst of Pd nanoparticles. The new HNT/Pd catalyst was used as catalyst in the Suzuki reaction under microwave irradiation. A set of solvents, times and bases was screened and the best experimental conditions were obtained when the reactions were carried out for 10 minutes in water/ethanol at 120 °C in presence of K2CO3 as base. Good recyclability was observed. The new catalytic system was employed both in 1 mol% or 0.1 mol%. The palladium catalyst displays good activity allowing the synthesis of several biphenyl compounds in high yields working with only 0.1 mol% of palladium loading.