Cationic organoiron polyelectrolyte three-arm stars

With nucleophilic aromatic substitution and ester condensation reactions, several new first-generation dendrimers and star-shaped molecules containing cationic cyclopentadieryl iron moieties were prepared. Although the solubility of the organoiron star-shaped molecules with ether bridges in polar solvents was found to decrease with an increase in the size of the molecule, the addition of ester linkages resulted in a sharp decrease in the solubility, regardless of the size. The thermal behavior of these molecules was examined with differential scanning calorimetry and thermogravimetric analysis. The glass-transition temperatures (T-g's) of these star-shaped molecules ranged from 123 to 170 degrees C. However, the addition of the ester functionality allowed for an increase in the T-g's to 151-194 degrees C. The star-shaped molecules were thermally stable up to 200 degrees C, above which a loss of the cationic cyclopentadienyl iron moieties occurred. Degradation of the ester chains started at 321 degrees C, and degradation of the ether chains started at 408 degrees C. Electrochemical studies of the ether star-shaped molecules showed a reduction of the 18-electron iron centers to 19-electron centers. This redox system was reversible at low temperatures, whereas it was irreversible at room temperature. Moreover, an increase in the number of metal moieties caused an overlap and broadening of the redox wave. Viscosity studies showed a polyelectrolyte effect for the organoiron star-shaped molecules. (c) 2005 Wiley Periodicals, Inc.