A multi-O₂ complex derived from a copper(I) dendrimer

The high-pressure reaction of 2-vinylpyridine with the primary amines of four consecutive generations of poly(propylene imine) dendrimers (DAB-dendr- (NH₂)(n)) (n = 4, 8, 16, 32) yielded dendrimers with bis[2-(2- pyridyl)ethyl]-amine (PY2) ligands. The complexation of the new dendrimers with metal ions was investigated by a variety of techniques. The reaction of the first- and fourth-generation dendrimers (n=4 and 32, respectively) with Zn(II)(ClO₄)₂ was studied by ¹H NMR titration, and the complexation of all new dendrimers with Cu(II)(ClO₄)₂ was investigated by UV/Vis and EPR spectroscopy. Quantitative coordination of one metal ion per PY2 group was demonstrated in all cases. A UV/Vis titration of the fourth-generation dendrimer DAB-dendr-(PY2)₃₂ in dichloromethane with [Cu(I)(CH₃CN)₄](ClO₄) in acetonitrile revealed that approximately 30 Cu(I) ions were bound. Low-temperature UV/Vis spectroscopy of this complex in dichloromethane at -85°C in the presence of dioxygen showed that approximately 60-70% of the copper centers can bind dioxygen, corresponding to 10-11 of these molecules per dendrimer molecule. This complex can be considered a synthetic analogue of hemocyanin, the copper-containing oxygen transport protein from the hemolymph of molluscs and arthropods.