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) have 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.

Electrochemistry of Poly(3,4‐alkylenedioxythiophene) Derivatives

“…[25] Similar behavior has been observed in the chemical polymerization (Ullmann coupling) of the first three N-BOC protected oligopyrroles. [26] The electropolymerization results were confirmed by the blue shift of k max corresponding to the p±p* transition obtained. This behavior is explained by the decreasing reactivity of the oxidized starting monomers with an increasing number of EDOT units leading to entrapment of shorter oligomers in the matrix during the polymerization.…”

A facile and novel approach toward synthetic polypyrrole oligomers functionalization of multi-walled carbon nanotubes as PtRu catalyst support for methanol electro-oxidation

“…The absorption peak at 222 nm is due to theinteractions of benzenoid transitions of the pyrrole ring of PPO, while the peak at 358 nm elucidates that the polymerization degree was not very high [32]. Compared to the absorption peak of pyrrole (212 nm), a blue shift was detected, which further illustrated that PPO was formed [37]. Interestingly, the absorption spectra of the PPO-MWCNTs dispersed in ethanol solution show a significantly peak at around ca.…”

Linear Monodisperse π-Conjugated Oligomers: Model Compounds for Polymers and More

“…Nevertheless, this reaction protocol can be useful if high yielding cross-coupling reactions, which are required in the iterative binomial synthesis, are simply not available or if rapid access to an entire series of monodisperse oligomers is desirable and subsequent chromatographic separations are applicable. Such a strategy has been used in our group and by others for the synthesis, for example, of monodisperse poly(triacetylene) oligomers (see Section 4.3), [34±39] for the synthesis of oligo(pyrrole)s, [40] or for the preparation of linear (1,3-diethynylcyclobutadiene)cyclopentadienylcobalt oligomers. [41] The practical limit of this method often lies in difficulties encountered during the chromatographic separation (such as by size-exclusion chromatography (SEC)) of oligomers with relatively low differences in molecular weight.…”