A novel di-compartmental bis-(2-hydroxyisophtalamide) macrocyclic ligand and its mononuclear Cu(ii) and Ni(ii) complexes

摘要

The synthesis and characterisation of the new di-compartmental bis-(2-hydroxyisophtalamide) macrocyclic pro-ligand, LH _6, which comprises two phenol-diamide units linked by ethylene bridges, is herein reported, together with its corresponding di-phenolate salt, [NBu _4] _2[LH _4]. The three macrocyclic compounds, [LH _4(OMe) _2] (protected ligand), LH _6 and [LH _4][NBu _4] _2 were fully characterised including X-ray crystallography for [LH _4(OMe) _2] and [NBu _4] _2[LH _4]. The results of solid-state and solution studies have indicated that the macrocycle can adopt specific conformations, which are influenced by H-bonding interactions as well as the deviation of the amide carbonyl relative to the phenol plane. LH 6 reacts with M ~(II)(acetate) _2·(H _2O) _6 (M = Ni, Cu) in a 1:1 ratio in the presence of 4 eq of [NBu _4](OH) in methanol to afford the dianionic [M(LH _2)] ~(2-) complexes, 1 ~(2-) and 2 ~(2-), respectively. The X-ray crystallography, EPR, NMR and UV-vis spectroscopic data, combined with DFT calculations, indicate that 1 ~(2-) and 2 ~(2-) are unique unsymmetrical square planar mononuclear complexes that are intramolecularly H-bonded. Thus, one macrocyclic compartment contains a M ~(II)-N _2O _2 centre resulting from the tetra-anionic di-phenolato di-amidato ligation; the other compartment possesses two protonated amide N-H groups that are H-bonded the coordinated phenolate O atoms. This represents a unique example in which a phenolate is both coordinated and intramolecularly H-bonded. This H-bonding appears unusually strong as revealed by N(H/D) exchange experiments; and may be responsible for the stability of the mononuclear complex, and the difficulty in isolating the corresponding dinuclear complex [M _2(L)] ~(2-).