Preparation and structure of zinc complexes containing pincer ligands and their application for Knoevenagel condensation in water

Two zinc complexes with Pybox ligands, 2,6-bis[4,4-dimethyloxazolin-2-yl]pyridine (Dm-pybox) (1a) and 2,6-bis[4-isopropyloxazolin-2-yl]pyridine (i-Pr-pybox) (1b), have been synthesized and characterized. Reactions of zinc chloride with the pyridine-based pincer ligands result in formation of (Dm-Pybox)ZnCl2 (2a) and (i-Pr-Pybox)ZnCl2 (2b), respectively. Both complexes have been characterized by elemental analysis, NMR and IR spectra. The molecular structures of 2a and 2b have been determined by X-ray crystallography. Complex 2b is efficient in catalyzing Knoevenagel condensation of ferrocenecarboxaldehyde with activated methylene compounds in water.