Synthesis of a bis(oxazoline)- N-carboxylate ligand and its Zn(II) complex that shows C–H⋯Cl hydrogen bonding

• Published in: Polyhedron 2006-11, Vol.25 (15), p.3025-3031
• Main Authors: Kang, Young Soon, Son, Jeong-Ho, Hwang, In-Chul, Ahn, Kyo Han
• Format: Article
• Language: English
• Subjects: Hydrogen bond; Oxazoline; Tetradentate ligand; Zn(II) complex
• ISSN: 0277-5387
• DOI: 10.1016/j.poly.2006.05.011

A novel N 3O-type chelate and its Zn(II) complex are synthesized. The chelate is a branched type N 3O ligand, ( S, S)-[Bis{(4-isopropyl-4,5-dihydrooxazol-2-yl)methyl}amino]acetic acid sodium salt, which was synthesized through a stepwise introduction of the oxazoline rings. The Zn(II) complex shows C–H⋯Cl–Zn hydrogen bonding both in the solid and solution states. A single crystal X-ray analysis of the Zn(II) complex supports the C–H⋯Cl–Zn hydrogen bonding, showing a microchannel structure. An efficient synthesis of a novel N 3O-type chelate and its Zn(II) complex is described. The Zn(II) complex shows C–H⋯Cl–Zn hydrogen bonding both in the solid and solution states. The chelate, ( S, S)-[bis{(4-isopropyl-4,5-dihydrooxazol-2-yl)methyl}amino]acetic acid sodium salt, is a new and branched type of N 3O ligand, featuring C 2-symmetric bis(oxazoline)- N-carboxylate. A key step of the ligand synthesis involved a stepwise introduction of the oxazoline rings to suppress side products otherwise resulted from one-step approach. Treatment of the sodium bis(oxazoline)- N-carboxylate with ZnCl 2 and subsequent removal of NaCl resulted in the corresponding Zn(II) complex. The Zn(II) complex showed an unusual downfield shift by the isopropyl methine protons on its 1H NMR spectrum, which suggests the C–H⋯Cl–Zn hydrogen bonding. An X-ray crystallographic analysis of the single crystals of the Zn(II) complex supports the C–H⋯Cl–Zn hydrogen bonding, showing a microchannel structure that encapsulates a linear array of chloroform molecules through other intermolecular hydrogen bonding interactions.