Oxazoline chemistry — Part IV: Synthesis and characterization of oxazoline complexes of the zinc halides

Abstract

The synthesis and characterization of 11 zinc halide derivatives that contain monodentate oxazoline ligands is described. The treatment of ether solutions of [ZnX2] (X = Cl, Br, I) with 2-aryl- or 2-methyl-2-oxazolines results in the formation of mildly hygroscopic complexes of the general formulae [ZnX2(ox)2] (ox = 2-methyl-2-oxazoline (1), 2,4,4-trimethyl-2-oxazoline (2), 2-phenyl-2-oxazoline (3), or 4,4-dimethyl-2-phenyl-2-oxazoline (4)), except in the case of ZnI2, which does not form an isolable complex — likely for steric reasons — with oxazoline 4. Treatment of [ZnBr2(4)2] with 1 reveals (1H NMR) that 1 only sluggishly displaces coordinated 4 at temperatures below 50 °C. The structural characterization, via single crystal X-ray diffraction, of six of the complexes, viz. [ZnI2(1)2], [ZnI2(2)2], [ZnX2(3)2] (X = Cl, Br, or I), and [ZnBr2(4)2], is also reported. All of these structurally characterized complexes are mononuclear zinc compounds with an overall distorted tetrahedral arrangement of the two halide and two oxazoline ligands around the zinc metal centre. The oxazoline series of complexes reported herein show little structural diversity, a facet which is in contrast to their substituted pyridine analogues.Key words: oxazoline, zinc, X-ray crystal structure, coordination complex, NMR spectroscopy, Zn(II).