Supported palladium nanoparticles: A general sustainable catalyst for microwave enhanced carbon-carbon coupling reactions

Synergism between nanocatalysts and microwave heating has emerged as a tool for sustainable organic synthesis. In the present investigation scope of palladium nanoparticle for ligand free carbon-carbon coupling reactions namely Suzuki, Hiyama, Heck and Sonogashira under microwave heating is investigated. Palladium nanoparticles of less than 10 nm dimension were impregnated onto a commercially available, non-functional, microporous polystyrene resin and were characterized by UV-vis spectroscopy, HRTEM attached with EDX, powder X-ray Diffraction (XRD) and ICP-AES. Highly pure coupled products in various reactions were obtained in 6-35 min using microwave heating in closed vials using benign mixed low boiling solvents, which otherwise require 4-30 h of inert atmosphere under conventional heating. Reaction parameters such as temperature, time and concentration of catalyst were optimized and catalyst was successfully recycled five to six times without any noticeable leaching or decrease in performance. Post reaction TEM analysis showed that size of the nanoparticles was still in the range of 3-10 nm. The catalyst was successfully used to synthesize asymmetric terphenyls in a single pot by sequential addition of aryl boronic acids. (C) 2016 Elsevier B.V. All rights reserved.