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

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 degrees 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.