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

Abstract

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.

Graphical Abstract

Keywords:

• Pincer
• Zinc
• Ferrocenecarboxaldehyde
• Knoevenagel
• Structure

Acknowledgements

We acknowledge financial support from the National Nature Science Foundation of China [grant number 21102004], and the Natural Science Foundation of the Anhui Higher Education Institutions of China [grant number KJ2011A146], the Project-sponsored by SRF for ROCS and Special and Excellent Research Fund of Anhui Normal University.