Syntheses, crystal structures and electrochemical properties of bis(catechol)s with acetylene group

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[Abstract] Three bis(catechol) compounds 5,5'-(buta-1,3-diyne-1,4-diyl) bis(3-tert-butylcatechol) (Biscat 1), 5,5'-(2,5-dimethoxy-1,4-phenylene)bis(ethyne-2,1-diyl)bis(3-tert-butyl-catechol) (Biscat 2) and 5,5'-(1,3-phenylene)bis(ethyne-2,1-diyl)bis(3-tert-butylcatechol) (Biscat 3) were obtained from cross-coupling reactions. Biscat 1 and Biscat 2 were characterized by X-ray crystal analysis and cyclic voltammetry (CV). The results from Xray crystal analysis shows that Biscat 1 and 2 possess a rod like structure with molecular lengths 14.7Å for Biscat 1 and 19.3Å for Biscat 2. In Biscat 1, the two catechol rings are not in the same plane and the dihedral angle of terminal catechol rings is about 25°. CVs for Biscat 1 and 2 were measured under alkaline conditions. An oxidation wave was observed corresponding to Sq-Sq (Sq: semiquinone)→Bq-Bq (Bq: benzoquinone) at around -300 mV. However, the redox waves disappeared when the CV scan was repeated. In contrast, Biscat 3 showed stable redox waves in the range from -1 V to ＋1.5 V even in alkaline conditions. These results suggest that Biscat 1 and 2 were converted into polymer or oligomer compounds (insoluble materials) through the Bq-Bq structures during repeat of the CV scans.