Synthesis, crystal structures and catalytic activities of new palladium(II)-bis(oxazoline) complexes

Palladium-bis(oxazoline) complexes (Pd-BOX-A and Pd-BOX-B) were synthesized and characterized by H-1, C-13 NMR, IR and elemental analysis. The molecular structures of the complexes were confirmed by single-crystal X-ray analysis. In both cases, the palladium center is coordinated by the nitrogen atoms of the two oxazoline rings and two chloride ligands in a distorted square planar geometry. Despite the fact that the bis(oxazoline) ligand is achiral, the asymmetrical substitution on the phenyl spacer and the rigid backbone of the complex Pd-BOX-A induce inherent chirality and the compound crystallizes as a racemic mixture. Both complexes were found to be highly effective catalysts for Suzuki-Miyaura, Mizoroki-Heck and Sonogashira cross-coupling reactions. They also show excellent catalytic activities toward carbonylative coupling reactions.