Star-Shaped Polyaromatic Ethers

Dendrimers and star polymers containing redox active sites have been utilized in the design of new types of catalysts, sensors, bioelectronic devices, and molecular batteries. Highly branched polymers containing arenes coordinated to oiganometallic moieties have been prepared witii chromium tricarbonyl, cyclopenta-dienyliron, and pentamethylcyclopentadienylrutheniiun moieties. Astruc and 

POLYMERS CONTAINING NEUTRAL AND CATIONIC CYCLOPENTADIENYLIRON MOIETIES IN THEIR STRUCTURES 

Figrae 26 shows the H and C NMR spectra of polymer 51e. The H NMR spectrum shows two peaks at 4.52 and 4.73 ppm, corresponding to the ferrocenyl cyclopentadienyl protons, Miile the singlet at 5.11 ppm corresponds to the cyclopenta-dienyl protons coordinated to the cationic iron center. In addition, the presence of two sets of doublets between 7.49 and 7.63 ppm confirms the incorporation of the 

CH carbons of the ferrocenyl cyclopentadienyl rings resonate at 70.89 and 72.68 ppm, while the quaternary cyclopentadienyl carbons can be seen at 71.3 7 ppm, and the cyclopentadienyl carbons pendent to the polymer backbone appear at 79.03 ppm. 

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The synthesis of a water-soluhle metallodendrimer containing six cationic cyclopentadienyliron moieties was also reported (249). This dendrimer was examined as a redox catalyst for the cathodic reduction of nitrates and nitrites to ammonia. Star-shaped polyaromatic ether complexes of cyclopentadienyliron were recently reported hy Ahd-El-Aziz and co-workers (250). These complexes contained up to 15 cationic cyclopentadienyliron moieties pendent to aromatic rings in the star branches (111). Electrochemical analysis of these star polymers showed that the iron centers underwent reversible reduction processes. 

Abd-El-Aziz and coworkers have reported the synthesis of star-shaped polyaromatic ethers containing up to 15 cyclopentadienyliron cations pendent to aromatic rings. Polymer 42 is an example of a water-soluble / exa-metallic star complex. Electrochemical studies showed that reduction processes for the inner and outer iron complexes could be distinguished for the hexa- and nonametallic stars. 

Star-shaped polyaromatic ethers complexed with cyclopentadienyliron cations (92) have been prepared, in which the metallic moieties are evenly spaced throughout the length of the macromolecular branches (Scheme 24). By altering the nature of the aromatic spacers between the complexed arenes, it was possible to alter the properties of these materials. Electrochemical analysis of these polymers demonstrated that the iron centers underwent reversible reduction processes. For the hexa-metallic stars (n=l), two distinct redox couples were observed at , /2=-1.20 and-1.30 V... 

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