Polyether dendritic cores

Cho B-K, Jain A, Nieberle J, Mahajan S, Wiesner U, Gruner SM, Tuerk S, Raeder HJ. Synthesis and self-assembly of amphiphihc dendrimers based on ahphatic polyether-type dendritic cores. Macromolecules 2004 37 4227-4234. 

Dendrimers based on aliphatic polyether type dendritic cores Characterisation of columnar structure [131]... 

Fig. 21. Dendritic polyrotaxanes with mechanical branching units containing covalently linked bis-dendrons and a core imit fused to polyether macrocycles...

Porphyrin complexes are particularly suitable cores to construct dendrimers and to investigate how the behavior of an electroactive species is modified when surrounded by dendritic branches. In particular, dendritic porphyrins can be regarded as models for electron-transfer proteins like cytochrome c [42, 43]. Electrochemical investigation on Zn-porphyrins bearing polyether-amide branches has shown that the first reduction and oxidation processes are affected by the electron-rich microenvironment created by the dendritic branches [42]. Furthermore, for the third generation compound all the observed processes become irreversible. 

Dendritic molecules with a single triethylene amine core surrounded by hyperbranched polyether sectors catalyze the nitro-aldol reaction between aromatic aldehydes and nitroalkanes (Eq. 3.5).15 The activity of the catalysts decreases when the generation number increases. No significant changes in stereo-control are observed on passing from lower- to higher-generation dendrimers. 

Similar dendritic architectures were formed by fixing polyether dendrons to a terpyridine [132] core unit by means of iron(II) ions [133]. 

The dendritic bis(oxazoline) ligands used were of those of zeroth to third generation Fig. 6.31. They were made up of two components, the catalytic core unit consisting of bis-oxazoline and the dendron composed of polyether units [49]. 

Following up this work, the same group recently published the synthesis of hybrid dendritic ligands containing a combination of dendritic chiral DPEN and Frechet polyether dendrons (Scheme 7) [50]. The solubility of these hybrid dendrimers was found to be controlled by the polyether den-dron. Compared with the simple core-functionalized systems displayed in Fig. 21, the hybrid dendrimers showed similar catalytic activity but reduced recyclability. 

Hawker and Frechet [50] prepared a dendritic macromonomer using the convergent-growth route to prepare a polyether dendron. The dendron core functional group (R in Scheme 9) was a hydroxymethyl group that was reacted with chloromethylstyrene to form the styrene-functionalized dendritic macromonomer. This macromonomer was copolymerized with slyrene monomer using standard free-radical polymerization conditions. 

---