Merging a Negatively Curved Nanographene and a Carbon Nanoring

Abstract

Two molecular nanocarbons result from merging a negatively curved nanographene and a carbon nanoring in two constitutional isomers of D 2 and C 2v symmetry, respectively. They were synthesized by attachment o f C -s h a p e d p a r a p h e n y l e n e p r e c u r s o r s t o 2 , 1 1 , 1 8 , 2 7tetrabromooctabenzo[8]circulene and the subsequent intramolecular Yamamoto coupling and reductive aromatization reactions. The flexible nature of octabenzo[8]circulene enabled two different ways of connection in the Yamamoto coupling reactions, leading to the two constitutional isomers. The D 2 isomer is shaped like a figure eight, as revealed by X-ray crystallography, and is resolved into two enantiomers by chiral HPLC. The synthesis of the C 2v isomer is regarded as a further step toward precision synthesis of carbon schwarzites through a bottom-up approach.

Cyclooctatetraene‐Embedded Carbon Nanorings

“…Purification by flash column chromatography on silica gel employing light petroleum and CH 2 Cl 2 as eluent led to the isolation of products including COTCNR1 (50 %), COTCNR2 (8 %), and COTCNR3 (17 %) in an overall yield of up to 75 %. On account of the fast conformational inversion (Figure 2c) of compound 1/1′ at 65 °C (with a rate constant of 3.22×10 3 s −1 , Figure S29), the observed ratio of these products can be attributed to their different reaction rates during the Yamamoto couplings, according to the Curtin–Hammett principle [12] …”

“…On account of the fast conformational inversion (Figure 2c) of Angewandte Chemie compound 1/1' at 65 °C (with a rate constant of 3.22×10 3 s À 1 , Figure S29), the observed ratio of these products can be attributed to their different reaction rates during the Yamamoto couplings, according to the Curtin-Hammett principle. [12] Although the mass spectra of COTCNR1 and COTCNR2 exhibit almost the same molecular ion peaks and isotope patterns (m/z of 606.2429 and 606.2350, respectively) in accordance with the same molecular formula of C 48 H 30 (Figures S9 and S12), the 1 H NMR spectra (Figure 2b) of COTCNR1 and COTCNR2 are very different. When recorded at 298 K in CD 3 SOCD 3 , COTCNR2 is characterized by a set of five proton signals similar to those observed for monomer 1, whereas the 1 H NMR spectrum of COTCNR1 is much more complicated.…”

Cyclooctatetraene‐Embedded Carbon Nanorings

“…On account of the fast conformational inversion (Figure 2c) of compound 1/1' at 65 °C (with a rate constant of 3.22×10 3 s À 1 , Figure S29), the observed ratio of these products can be attributed to their different reaction rates during the Yamamoto couplings, according to the Curtin-Hammett principle. [12] Although the mass spectra of COTCNR1 and COTCNR2 exhibit almost the same molecular ion peaks and isotope patterns (m/z of 606.2429 and 606.2350, respectively) in accordance with the same molecular formula of C 48 H 30 (Figures S9 and S12), the 1 H NMR spectra (Figure 2b) of COTCNR1 and COTCNR2 are very different. When recorded at 298 K in CD 3 SOCD 3 , COTCNR2 is characterized by a set of five proton signals similar to those observed for monomer 1, whereas the 1 H NMR spectrum of COTCNR1 is much more complicated.…”