Metal mediated degradation of tripodal imine–phenol ligands: designer ligands with metal ion designers

Abstract

Hydrated metal salts, M = Cu or Zn, promoted partial hydrolysis of tripodal imine–phenol ligands N[CH2CH2NCHC6H3(R)OH-2]3 (H3L) with concomitant formation of complexes of MII with the N-bearing fragment of the ligand which remains. With zinc(II) tetrafluoroborate hydrate, complexes [Zn{N[CH2CH2NCHC6H3(R)O-2](CH2CH2NH2)2}[BF4] (hereafter [ZnL′][BF4]) where R = H 1, 3-OCH3 2, 5-Br 3 or 5-NO2 4 were obtained; the crystal structure of 3 reveals that the zinc centre has a distorted trigonal bipyramidal geometry, with an [N3] trigonal plane and the salicylidene oxygen and tertiary nitrogen atom of L′ occupying the axial positions. The corresponding reaction of H3L with copper(II) perchlorate hexahydrate proceeded with analogous hydrolysis to yield dicationic complexes [Cu(HL′)][ClO4]2 where R = H 5, 3-OCH3 6, 5-Br 7 or 5-NO2 8. The crystal structure of 8·MeOH revealed protonation at a pendant aminoethyl nitrogen atom of L′, resulting in a four-co-ordinate square planar [N3O] donor set for CuII with the salicylidene oxygen atom trans to the tertiary nitrogen atom. In addition, for R = 5-NO2, crystals of a second compound 8a·MeOH, isolated from the mother-liquor of 8, have been shown by X-ray crystallography to be a five-co-ordinate complex [CuL′][ClO4] with a trigonal bipyramidal arrangement of the [N4O] donor atoms at the copper centre, isomorphous with the zinc complexes.