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

Reaction of 2,6-bis(dialkylaminomethyl)-3-alkylphenols (L) with ZnCl2 in ethanol leads to zwitterionic Zn(II) complexes [ZnCl2L]. An X-ray d iffraction study on the compound with L = 2,6-bis(dimethylaminomethyl) -4-tert-butylphenol reveals the presence of a mononuclear zincate comp lex, in which the distorted tetrahedral coordination of the metal cons ists of two chlorine atoms and the ligand L acting as a bidentate chel ating agent Dia the deprotonated phenol oxygen and one amino group. Mi gration of the phenolic hydrogen to the uncoordinated amino group in t he other ortho substituent generates an ammonium group whose positive charge balances the negative charge of the zincate centre. This ammoni um group forms an intramolecular N-H ... O hydrogen bond with the coor dinated phenoxide oxygen. Complex stability is enhanced by the reducti on of electron density accompanying the formation of the phenoxide 'br idge' between the Zn atom and the ammonium proton. H-1 and (13C) NMR s pectroscopies indicate that ligand dissociation does not occur and the complexes retain their solid-state structure in solution.