Mononuclear zinc(II) complexes of o-amino phenolate ligands. X-Ray structure of the zwitterionic [ZnCl2L] compound with 2,6-bis(dimethylaminomethyl)-4-tert-butylphenol

Abstract

Reaction of 2,6-bis(dialkylaminomethyl)-4-alkylphenols (L) with ZnCl₂ in ethanol leads to zwitterionic Zn(II) complexes [ZnCl₂L]. An X-ray diffraction study on the compound with L=2,6-bis(dimethylaminomethyl)-4- tert-butylphenol reveals the presence of a mononuclear zincate complex, in which the distorted tetrahedral coordination of the metal consists of two chlorine atoms and the ligand L acting as a bidentate chelating agent via the deprotonated phenol oxygen and one amino group. Migration of the phenolic hydrogen to the uncoordinated amino group in the other ortho substituent generates an ammonium group whose positive charge balances the negative charge of the zincate centre. This ammonium group forms an intramolecular N–H···O hydrogen bond with the coordinated phenoxide oxygen. Complex stability is enhanced by the reduction of electron density accompanying the formation of the phenoxide ‘bridge’ between the Zn atom and the ammonium proton. ¹H and ¹³C NMR spectroscopies indicate that ligand dissociation does not occur and the complexes retain their solid-state structure in solution.