(NHC)-Pd(II) complexes with hydrophilic Nitrogen ligands;catalytic properties in neat water

The cleavage reactions of the dimers [(NHC)PdX2]2 with hydrophilic N-donors, L, afforded the mixed-ligand complexes of the type trans-[(NHC)LPdX2] (X = Cl or Br; NHC = 1,3-dialkylbenzimidazol-2-ylidene (BIm) or bis(imino)acenaphthene-annulated bis(2,6-diisopropylphenyl)imidazol-2-ylidene (BIAN-IPr); L = diethanolamine (DEA), morpholine (MOR), and 3-pyridinecarboxylic acid (3-PCA)). The new complexes (1--3) were characterized by elemental analysis and spectroscopic methods and the molecular structure of 1a was determined by X-ray diffraction studies. These complexes were applied in the Suzuki--Miyaura cross-coupling reaction of phenylboronic acid with aryl halides in neat water. The activities of catalysts were monitored by gas chromatography--flame ionization detector and nuclear magnetic resonance. Whereas the complexes with DEA or 3-PCA ligands did not show significant difference in the activity, the BIAN-IPr complexes 1b and 3b bearing DEA and 3-PCA, displayed the highest catalytic activity at 100 °C.