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Synthesis of partially and fully fused polyaromatics by annulative chlorophenylene dimerization

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Science  26 Jan 2018:
Vol. 359, Issue 6374, pp. 435-439
DOI: 10.1126/science.aap9801

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How to get two bonds for the price of one

For more than a century, we have known how to couple aryl chlorides at the sites of their C-Cl bonds to form a single C-C bond. Koga et al. found that palladium catalysis can instead activate these C-Cl bonds to attack nearby aromatic C-H bonds in a terphenyl molecular framework. The reaction thereby produces a new ring, fused to the original rings on either side. Polycyclic compounds of this sort are of particular interest in optoelectronics research because of their expansive electron delocalization.

Science, this issue p. 435

Abstract

Since the discovery by Ullmann and Bielecki in 1901, reductive dimerization (or homocoupling) of aryl halides has been extensively exploited for the generation of a range of biaryl-based functional molecules. In contrast to the single-point connection in these products, edge-sharing fused aromatic systems have not generally been accessible from simple aryl halides via annulation cascades. Here we report a single-step synthesis of fused aromatics with a triphenylene core by the palladium-catalyzed annulative dimerization of structurally and functionally diverse chlorophenylenes through double carbon-hydrogen bond activation. The partially fused polyaromatics can be transformed into fully fused, small graphene nanoribbons, which are otherwise difficult to synthesize. This simple, yet powerful, method allows access to functional π-systems of interest in optoelectronics research.

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