DOI: 10.1002/chem.201100443 Evidence for Fully Conjugated Double-Stranded Cycles Malte Standera, [a] Rolf Häfliger, [b] Renana Gershoni-Poranne, [c] Amnon Stanger, [c] Gunnar Jeschke, [d] Jacco D. van Beek, [e] Louis Bertschi, [b] and A. Dieter Schlüter* [a] Introduction Chemists have dreamed of fully unsaturated, double-strand- ed hydrocarbon cycles like [n]cyclacenes I, buckybelts II, cy- clo[n]phenacenes III, and Vçgtle-belts IV for several de- cades (Figure 1). [1] In addition to their aesthetic appeal, they are also important for the study of certain aspects of host– guest behavior, including hydrogen bonding between weak donors and p systems, the formation of polyrotaxanes, the endo/exo cyclic selectivity of reactions, the dynamics of tran- sition-metal fragments complexed to the p system, and their redox behavior, including the aspect of maximum charge- ACHTUNGTRENNUNGability. They would also serve as models for their open- chain linear analogues, the ladder polymers, [2] and some of them could be developed into novel, shape-persistent con- stituents for molecular constructions. [3] Finally, such com- pounds would enrich the world of larger, all-carbon struc- tures such as fullerenes, carbon nanotubes, and graphene. Although there has been significant progress in their synthe- sis, a breakthrough has not yet been achieved. Several double-stranded cycles with the appropriate carbon skele- tons have been synthesized and even a few chemical modifi- cations aimed at an expansion of the conjugated parts have been accomplished. [4] However, attempts to generate any of the above fully conjugated targets failed altogether and only recently has synthesis gotten close, specifically the work of Abstract: A chain of circumstantial evi- dence for the existence of the first fully conjugated, double-stranded cycles is presented. The products have the struc- ture of the belt-region of fullerene C 84 (D 2 ) and carry either four hexyl chains or four phenyl groups. The unsubstitut- ed parent cycle is also presented. The chain of evidence is mainly based on mass spectrometric analysis and trap- ping reactions, the latter being support- ed by quantum mechanical calcula- tions. It is also of importance that the phenyl-substituted and unsubstituted products cannot undergo a [1,5] hydro- gen shift, the only reasonable side-reac- tion that recently could not be exclud- ed for the alkyl-substituted analogue. It is concluded that the fully aromatic tar- gets truly exist in the gas phase. Whether they can be generated in solu- tion under the applied conditions cannot yet be firmly decided; theoreti- cal evidence speaks against. Keywords: aromaticity · conjuga- tion · mass spectrometry · thermo- chemistry · trapping experiments [a] Dr. M. Standera, Prof. A. D. Schlüter Laboratory of Polymer Chemistry Department of Materials, ETH Zürich Wolfgang-Pauli-Strasse 10, HCI 541, 8093 Zürich (Switzerland) E-mail : dieter.schlueter@mat.ethz.ch [b] R. Häfliger, L. Bertschi Mass Spectrometry Unit, Laboratory of Organic Chemistry Department of Chemistry and Applied Biological Sciences ETH Zürich Wolfgang-Pauli-Strasse 10, 8093 Zürich (Switzerland) [c] R. Gershoni-Poranne, Prof. A. Stanger Schulich Faculty of Chemistry and The Lise-Meitner-Minerva Center for Computational Quantum Chemistry, Technion Technion City, 32000 Haifa (Israel) [d] Prof. G. Jeschke Laboratory of Physical Chemistry, ETH Zürich Wolfgang-Pauli-Strasse 10, HCI F 231, 8093 Zürich (Switzerland) [e] Dr. J. D. van Beek Laboratory of Solid-State NMR Spectroscopy Department of Chemistry and Applied Biological Sciences ETH Zürich Wolfgang-Pauli-Strasse 10, 8093 Zürich (Switzerland) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201100443. Figure 1. Fully conjugated, belt-like compounds, [n]cyclacenes I (n = 12) and buckybelts II (shown with two repeat units), and angularly annulated congeners, the cyclo[n]phenacenes III (n = 12) and the Vçgtle belts IV (shown with six repeat units). The arrows help identify the repeat units. Chem. Eur. J. 2011, 17, 12163 – 12174  2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 12163 FULL PAPER