Synthesis and Binding Properties of Dendritic Oxybathophenanthroline Ligands towards Copper(II)

Abstract

AbstractDendritic oxybathophenanthroline ligands (generation 0 to 3) have been synthesized by treatment of 4,7‐bis(4′‐hydroxyphenyl)‐1,10‐phenanthroline with the corresponding Fréchet‐type dendrons carrying a benzylic bromide function at the focal point. The complexation of copper(II) has been studied by liquid–liquid extraction using the radioisotope 64Cu and time‐resolved laser‐induced fluorescence spectroscopy (TRLFS) in organic media indicating the formation of 1:3 complexes (Cu:dendritic ligand). Electronic and EPR spectroscopy were used to characterize the copper(II) chromophore, which is shown to have the expected distorted square‐planar geometry with two phenanthroline donors coordinated to the copper(II) center. The third dendritic ligand therefore is proposed to be bound by secondary interactions. The stability constants of the 1:3 complexes were found to be in the order of log K ≈ 16 in CHCl3. On the other hand, increasing generation of the dendritic Fréchet‐type branches leads to enhanced shielding of the copper ion from the environment. Additional information about this behaviour was obtained by the fluorescence lifetimes, which are much less influenced upon addition of copper(II) salt to solutions of the higher generation ligands. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)