Syntheses and Electropolymerization of Carboranyl-Functionalized Pyrroles and Thiophenes

A series of 3- and 3,4-substituted pyrroles and thiophenes with electron-withdrawing carboranylmethylphenyl groups has been synthesized in high yields via the coupling of either pyrrole- and thiopheneboronic acids with carboranylmethylphenyl halides or bromo-functionalized pyrroles with carboranylmethylphenylboronic acid. Some of these compounds were efficiently electropolymerized in acetonitrile or dichloromethane. The resulting conducting polymer films were reversibly p-doped in the range 0.0–0.25 V vs Ag/Ag⁺ 10⁻² M for the pyrrole-based polymers and p-/n-doped at ca. 0.60 and −1.90 V for the thiophene-based polymers. As a consequence of the presence of the carborane cages, the electroactivity of the polythiophenes was not degraded when highly oxidizing potentials (up to 2.0 V) were applied. In contrast, the polypyrrole derivatives were rendered totally electroinactive under similar conditions. The UV–vis spectroscopy analysis of the electrogenerated polymers revealed that the introduction of carborane cages resulted in either an enhancement or a stabilization of the mean conjugation length of the resulting polymers in comparison with the reference phenyl-substituted polypyrrole and polythiophene. In addition, these functionalized materials show unusual thermal stability for conducting polymers with a mass loss less than 10% up to 500 °C, under an inert atmosphere.