A Merrifield resin supported Pd–NHC complex with a spacer(Pd–NHC@SP–PS) for the Sonogashira coupling reaction under copper- and solvent-free conditions

Abstract

Synthetic applications of a polymer supported air-stable palladium NHC complex with a spacer (catalyst 6, Pd–NHC@SP–PS) and without a spacer (catalyst 7, Pd–NHC@PS) have been studied for the Sonogashira cross-coupling reaction. The catalysts were prepared by immobilizing pre-formed IL on the polymer and reacting the resultant modified polymer with Pd(OAc)₂ in THF at 60 °C. Both the catalysts were characterized using IR, SEM, EDS, ICP, XPS and TGA/DTA. Catalyst 6 has been found to be more active than catalyst 7, due to the greater accessibility of active catalytic sites, for a variety of aryl bromides and terminal alkynes in solvent and copper free Sonogashira cross-coupling reactions under aerobic conditions. The effect of the spacer, nature of base, reaction temperature, the catalyst loading as well as reusability was also investigated.