A palladium chelating complex of ionic water-soluble nitrogen-containing ligand: the efficient precatalyst for Suzuki-Miyaura reaction in water

An ammonium-functionalized water-soluble bidentate nitrogen-containing ligand (3) and its palladium chelating complex (4) have been easily prepared from the commercial available starting materials in high overall yields. The charge distributions and molecular orbital analyses of 3, 4 and non-ionic hydrophobic analogue (2a) based on the optimized structures were implemented. The crystal structure of 4 has been established by single-crystal X-ray diffraction. The water-soluble palladium complex was a much more effective catalyst than 2a in palladium-catalyzed Suzuki-Miyaura cross-coupling reaction in air and pure water. High catalytic activity of aryl chlorides and aryl bromides was observed. The mercury drop test, poison experiments and TEM analysis of the catalytic solution showed Pd(0) were involved in catalysis. The palladium nanoparticles of 3.0 +/- 0.6 nm were formed after the catalytic reaction, they were stabilized by synergetic effect of coordination and electrostatic interactions from the ammonium-functionalized chelating ligand. No precipitate was observed when the aqueous nanoparticles were stored in air for months.