M. Bera, Shivajirao L. Gholap, Paul Hommes
Nov 25, 2013
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Journal
Advanced Synthesis & Catalysis
Abstract
Starting from easily accessible precursors we describe the preparation of a series of branched oligo(2-thienyl)- and oligo(2,2′-bithienyl)-substituted pyridine derivatives. With palladium-catalyzed cross-coupling reactions of pyridyl nonaflates/triflates as key steps we synthesized 2,6-di(2-thienyl)pyridines bridged by thiophene or benzene rings. By selective bromination of 2,6-di(2-thienyl)pyridine and 2,4,6-tri(2-thienyl)pyridine and subsequent coupling reactions an access to oligo(2,2′-bithien-5-yl)-substituted pyridine derivatives was gained. The constitution and solid state conformation of 2,6-bis(2,2’-bithien-5-yl)pyridine was determined by X-ray analysis. This series of new pyridine-thiophene conjugates was systematically investigated by UV/vis spectroscopy. Large Stokes shifts in the neutral and protonated form were observed. The electrochemical oxidation of two typical compounds was studied, however, these oxidations were irreversible forming a polymeric film at the anode. As a selected example, a thiophene-bridged 2,6-di(2-thienyl)pyridine derivative was also investigated by scanning tunneling microscopy showing an interesting self-assembly into a highly ordered monolayer on highly oriented pyrolytic graphite.