A stereodynamic tripodal ligand with three different coordinating arms: Synthesis and zinc(II), copper(I) complexation study

Abstract

A tetradentate tripodal ligand containing a chiral center and three different coordinating arms was designed and synthesized. Its complexation properties with Zn(II) and Cu(I) were studied by NMR and optical spectroscopy. NMR experiments demonstrated the formation of two diastereomers, indicating the stabilization of the central tertiary amine configuration by metal coordination. The inversion of pyramidalization of the central tertiary amine of the ligand was found to be highly dependent upon metal ion, solvent, and temperature. Dynamic NMR measurements were used to estimate the energy of activation required for nitrogen atom inversion. Finally, absorption and circular dichroism measurements confirmed the expectation that metal complexes of the ligand gave rise to circular dichroism but that such spectra were not characterized by exciton-coupling, in contrast to previously described ligands containing two identical arms with strong chromophores.