Synthesis of multi-imidazolium salt ligands containing calixarene fragments and their N-heterocyclic carbene Ag(I) macrocyclic complexes

摘要

The unsymmetric bis-imidazolium salts ligands 4a and b were prepared by stepwise reactions of 2,6-bis(bromomethylene)-4-(t-butyl)anisole (1) with two different N-substituted imidazoles. Reaction of the bis-imidazolium ligands with Ag2O in acetonitrile gave the dinuclear bis(N-heterocyclic carbene) complexes 5a and b. The molecular structure of complex 5a was determined by single-crystal X-ray diffraction analysis. In complex 5a and b, the two C-carbene-AB-C-carbene axes are in a crossed conformation, two O atoms from phenoxyl groups weakly coordinate to different Ag ions and the two p-t-butylphenoxyl groups adopted a staggered conformation. To regulate the molecular shape of the N-heterocyclic carbene Ag(I) macrocyclic complexes, two tetradentate imidazolium ligands (9a and b) were prepared. The bimetallic NHC-Ag(I) complexes 10a and b were obtained by the reaction of 9a and b and Ag2O in acetonitrile. Constrained by the chain (the dioxoethylene or dioxomethylenebenzene chain in 10a or 10b, respectively) at the O-position of the phenoxyl group, the two p-methylphenoxyl groups in complexes 10a and b might be predicted to have a cone conformation. The ligands and the corresponding NHC metal complexes have been characterized by elemental analysis, H-1 NMR and C-13 NMR, HRMS spectra, as well as TGA and DTA spectra being determined for complexes 10a and b. The TGA curves show that these NHC-Ag complexes have good thermal stability. (C) 2014 Elsevier Ltd. All rights reserved.