Application of a zwitterionic palladium complex as a metal precursor of recyclable palladium nanoparticles for catalyzing Suzuki-Miyaura coupling reactions

An efficient recyclable catalyst system for Suzuki-Miyaura coupling reactions in water was developed based on a zwitterionic palladium complex bearing an imidazolium-based carbon donor and tricyclohexylphopshine. The complex served as an effective metal precursor for the formation of catalytically active palladium nanoparticles. The addition of excess n-tetrabutylammonium bromide (TBAB) was essential for stabilizing the nanoparticles in water. After several catalytic runs, a phase separation was observed and TBAB became an ionic liquid phase, supporting the palladium nanoparticles. The nanoparticles was recyclable, which allowed up to nine consecutive catalytic runs to be completed without significant loss of activity. The recyclable catalyst system allowed the use of unreactive aryl chlorides as substrates, changes of substrates between catalytic runs, manipulation of the reactions in air, and upscaling of the catalytic reaction.