Syntheses and nickel coordination properties of cyclen substituted with mixed stilbene/poly(ethylene glycol) dendritic arms

Abstract

AbstractWe synthesized a series of cyclens substituted with mixed stilbene and poly(ethylene glycol) dendritic arms. All dendrimers terminated with different peripheral groups had good solubility in common organic solvents, and dendrimers terminated with CO2H groups (CO2H‐dendrimers) were also soluble in alkaline solutions. The nickel coordination properties of these dendrimers were investigated in organic solvents. Dendrimers terminated with CN groups (CN‐dendrimers) and the second‐generation CO2H‐dendrimer [(CO2H)8L2] could produce pentacoordinated nickel complexes; the third‐generation CO2H‐dendrimer [(CO2H)16L3] could form tetra‐ and pentacoordinated nickel complexes, and the nickel complex of the fourth‐generation CO2H‐dendrimer [(CO2H)32L4] could not be obtained. This result was due to the fact that the globular surface of (CO2H)16L3 formed a hydrogen‐bond network that selectively penetrated cations and inhibited the access of anions to the core. The formation of the hydrogen‐bond network was confirmed by Fourier transform infrared, 1H NMR, and fluorescence data. The CN‐dendrimers could not form hydrogen bonds on the surface, and the first‐ and second‐generation CO2H‐dendrimers could not form intramolecular hydrogen‐bond networks. Therefore, they had no selectivity for positive nickel ions and negative chloride ions. (CO2H)32L4 could not produce a nickel complex because it had a crammed backbone structure that could not penetrate nickel and chloride ions. Therefore, it was possible to control the ion access of cations and anions with the hydrogen‐bond network of (CO2H)16L3. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5414–5428, 2005