Macrocyclic trinucleating ligands for the cocomplexation of two "soft" (Cu2+, Ni2+, or Zn2+) metal centers and one "hard" (Ba2+ or Cs+) metal center
作者:Frank C. J. M. Van Veggel、Martinus Bos、Sybolt Harkema、Henry Van de Bovenkamp、Willem Verboom、Jan Reedijk、David N. Reinhoudt
DOI:10.1021/jo00001a043
日期:1991.1
Macrocyclic heterotrinucleating ligands that have one compartment for complexation of alkaline or alkaline earth cations and two compartments for transition-metal cations have been synthesized. The Ba2+-templated (2 + 2) macrocyclization of the dialdehydes 3a and 3b with the diamine 8 yielded the barium complexes (9b, 9e) in high yield. The Cs+-templated (2 + 2) macrocyclization of the dialdehyde 3a and the diamine 8 gave the cesium complex 9c. The mononuclear complexes were converted into the heterotrinuclear complexes 10a-h by reaction with 2 equiv of copper, nickel, or zinc acetate. The barium complex 9b, the dicopper/barium complex 10a, and the dinickel/barium complex 10b have been analyzed by X-ray crystallography. In all three crystal structures the O10 cavity is folded around the barium cation. The copper-copper distance in the dicopper/barium complex 10a is 3.50 angstrom and the nickel-nickel distance in the dinickel/barium complex 10b is 3.42 angstrom. The electrochemistry of the copper-containing heterotrinuclear complexes 10a, 10d, and 10g and the nickel-containing heterotrinuclear complexes 10b, 10e, and 10h has been studied by polarography, cyclic voltammetry, and coulometry in DMSO. The dinickel/barium complex 10b was also studied by Kalousek polarography. The dicopper/metal complexes 10a, 10d, and 10g all show a copper-copper interaction, which is the strongest for the dicopper/barium complex 10a. Coulometry revealed that the complexes 10a, 10d, and 10g undergo a reduction with two electrons, and cyclic voltammetry showed that the reduction/oxidation processes of 10a, 10d, and 10g are chemically reversible. The reduction/oxidation processes of the nickel-containing heterotrinuclear complexes 10b, 10e, and 10h are complicated by adsorption phenomena. Frozen EPR spectra of 10a and 10g exhibit typical triplet spectra with a zero-field splitting of about 0.04 cm-1. This behavior is typical for Cu(II) dimers and confirms that both Cu(II) cations are also exchange coupled in solution. A Cu-Cu distance in solution of 3.6 angstrom agrees best with the spectra. Attempts to add exogenous bridging ligands like F- and imidazolate were unsuccessful.