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

We 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 CO 2 H groups (CO 2 H‐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 CO 2 H‐dendrimer [(CO 2 H) 8 L2] could produce pentacoordinated nickel complexes; the third‐generation CO 2 H‐dendrimer [(CO 2 H) 16 L3] could form tetra‐ and pentacoordinated nickel complexes, and the nickel complex of the fourth‐generation CO 2 H‐dendrimer [(CO 2 H) 32 L4] could not be obtained. This result was due to the fact that the globular surface of (CO 2 H) 16 L3 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, 1 H NMR, and fluorescence data. The CN‐dendrimers could not form hydrogen bonds on the surface, and the first‐ and second‐generation CO 2 H‐dendrimers could not form intramolecular hydrogen‐bond networks. Therefore, they had no selectivity for positive nickel ions and negative chloride ions. (CO 2 H) 32 L4 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 (CO 2 H) 16 L3.