Polythiophenes Containing In-Chain Cobaltabisdicarbollide Centers

Abstract

New cobalt(III) bis(dicarbollide) complexes covalently linked to two 2-oligothienyl units have been synthesized and electropolymerized in acetonitrile electrolyte in order to produce the corresponding polythiophene films containing in-chain metallic centers. The polymer films electrogenerated from the bithienyl (4b) and terthienyl (4c) derivatives display redox processes attributed to the Co(III)/Co(II) couple at ca. −1.1 V vs SCE and to the p-doping/undoping of the expected quaterthienyl and sexithienyl segments at ca. 0.8 V vs SCE. In contrast, the anodic oxidation of the thienyl (4a) derivative leads to passivation of the electrode surface. As the length of the oligothiophene substituents increases, the metallic and dicarbollide cage carbon atoms contributions in the HOMO decrease dramatically so that the highest occupied frontier orbitals of 4b and 4c can be considered as almost purely oligothiophene-based. From further UV-vis spectroscopy analysis, it is demonstrated that the polymer incorporating the sexithienyl segments is more conjugated than that with the quaterthienyl segments as the absorption maximum for the interband π-π* transition was observed at 410 and 448 nm for poly(4b) and poly(4c) respectively. Furthermore, these polymers display a more extended degree of conjugation than the parent oligothiophenes. Such features indicate a significant electronic delocalization through the cobaltabisdicarbollide moiety. Their conducting probe atomic force microscopy characterization indicates that poly(4b) and poly(4c) behave like heavily doped semiconductors rather than pure semiconductors. Mean conductivity values extracted from the current-voltage profiles are 1.4 ×10 −4 and 7.5 ×10 −4 S cm −1 for poly(4b) and poly(4c), respectively. Such materials are found to be efficient for the electrocatalytic reduction of protons to dihydrogen, as exemplified for poly(4b). The overpotential for hydrogen evolution is significantly decreased by ca. 230 mV with respect to that obtained with the bare electrode (measured for a current density of 1.4 mA cm −2 in the presence of 20 mM HBF 4 ). Supporting Information Available: High-resolution ESI mass spectra of 4a, 4b, and 4c; UV-vis spectra of 4a, 4b, and 4c (PDF). This material is available free of charge via the Internet at

Synthesis and electropolymerization of a series of 2,2′-(ortho-carboranyl)bisthiophenes

“…-(6) was used as doping agent for the electropolymerization of monomers; [16][17][18][19] (ii) pyrrole and thiophene monomers were modified by functionalization at the 2-position [20] and the N-position (e.i. 7) [21] with anion (6), followed by electropolymerization to form the self-doped polymers under suitable conditions; (iii) monomers were modified by using neutral carboranes (o-, m-, p-) at the 2-position [22,23] and at the 3 and/or 4-positions (e.g.…”

“…Such intriguing effects of the film thickness on the electroactivity of the surface-confined reducible couple have already been reported by us with polythiophenes containing in-chain cobaltabisdicarbollide centers. [20] It must be kept in mind that the cathodic process occurs within a potential range where the polymer is in its neutral reduced state, i.e. in its electronically insulating state.…”

Metal‐containing Polymers via Electropolymerization

“…Hence, the obtained polymer films could be used successfully for the catalysis of Suzuki‐, Sonogashira‐, and Heck‐type reactions. The electrocatalytic reduction of protons to hydrogen, with an overpotential reduction of 230 mV by using electrodes coated with the electropolymerized cobalt(III) bis (dicarbollide) complexes 10 ( Figure ), was presented by Vicente and co‐workers 69. Electrocatalytic oxidation of methanol was studied by Ojani et al The authors coated the surface of a carbon paste electrode with an electrochemically synthesized poly(1,5‐diaminonaphthalene) and coordinated nickel(II) ions by dipping into a nickel chloride solution.…”

Electrochemical behaviour of oxygen reduction on polymer carbon electrodes in alkaline media

“…The maximum pyrolysis temperature of the electrodes preparation is 700°C. Cobalt/carbon electrodes for the oxygen reduction are well docu mented in the open literature [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44]. The activity of the prepared PC electrodes in comparison to that of a platinum (Pt) electrode is also illustrated.…”