Cyclooctatetraene-Embedded Carbon Nanorings

Cyclooctatetraene-Embedded Carbon Nanorings

Author: ChemistryViews

Carbon nanorings are conjugated macrocycles that can have interesting electronic, photophysical, and
supramolecular properties and might be useful for the bottom-up synthesis of structurally uniform carbon nanotubes (CNTs). The synthesis of carbon nanorings can be made difficult by the strain caused by the distortion of the aromatic rings. Thus, bent, v-shaped building blocks can be useful precursors in this context. Cyclooctatetraene (COT), for example, adopts a boat-like confirmation and can be fused with aromatic units (example pictured above on the left) to obtain such precursors.

Qing-Hui Guo, Zhejiang University and ZJU-Hangzhou Global Scientific and Technological Innovation Center, Hangzhou, China, Tsinghua University, Beijing, China, and colleagues have developed a method for the efficient syntheses of three COT-embedded carbon nanorings (COTCNRs, pictured), using a one-pot nickel-mediated Yamamoto coupling of 2,9-dibromodibenzo[a,e]cyclooctatetraene. This precursor was first prepared from 4-bromo-1,2-bis(dibromomethyl)benzene and then treated with Ni(COD)2 (COD = 1,5-cyclooctadiene) and 2,2′-bipyridine to induce the desired coupling reactions.

Under these conditions, macrocyclic products with different numbers of dibenzocyclooctatetraene units were formed. The team purified the products using flash column chromatography and obtained, e.g., COTCNR1, COTCNR2, and COTCNR3 (pictured) in yields of 50 %, 8 %, and 17 %, respectively. COTCNR1 and COTCNR2 are isomers with rigid structures, while the tetramer COTCNR3 has a flexible carbon skeleton. The researchers found that COTCNR3 can form host-guest complexes with fullerenes (C60 and C70). The resulting complexes form linear supramolecular wires in the solid state. The team observed that these supramolecular wires have electrical conductivities on the order of 10−7 S cm−1 (for C60COTCNR3) and 10−8 S cm−1 (for C70COTCNR3) under ambient conditions.


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