Well-Defined Oligo(pyrrole-2,5-diyl)s by the Ullmann Reaction

Abstract

The Ullmann coupling reaction has been used to polymerize N-t-BOC-2,5-dibromopyrrole into well-defined oligo(pyrrole-2,5-diyl)s. After optimization of the reaction conditions, i.e. using 1 wt equiv of Cu-bronze in DMF at 100 "C for 1 h, oligomers up to 25 repeating pyrrole units are obtained. Starting from 5,5‘- and 5,5"-dibrominated N-t-BOC protected bi- and terpyrrole as monomers, the polymerization is slower and a lower degree of polymerization is observed, yielding oligomers with an even lower molecular weight than those resulting from N-t-BOC-2,5-dibromopyrrole. The first 20 oligomers of poly(N-t-BOC-pyrrole)h ave been isolated by preparative HPLC. Characterization of the individual oligomers shows that they all are hydrogen terminated and possess a perfect 2,5-linkage: oligo(pyrro1e-2,5-diyl)s. The isolated oligomers have been used to study the optical and electrical properties of the oligomers as a function of chain length.