1,3,5-tricorannulenylbenzene: stereochemistry, reduction and supramolecular dimerization of a branched oligocorannulene David Eisenberg a , Jennifer M. Quimby b , Lawrence T. Scott b ** and Roy Shenhar a * Oligocorannulenes are polyarenes composed of several corannulene units that are covalently linked. Their behavior arises both from the diverse properties of each corannulenyl unit and from the interactions between them. In this paper, we pres- ent the synthesis, stereochemistry, reduction, and self-assembly properties of a novel type of oligocorannulene: branched 1,3,5-tricorannulenylbenzene. Several stereodynamical elements combine to give rich stereochemistry: bowl-to-bowl in- version, rotation about the aryl-aryl single bonds, and residual stereoisomerism of molecular propellers. Reduction with lithium metal yields an intermediate hexaanion and ultimately produces a highly charged dodecaanion. Self-diffusion NMR demonstrates that the dodecaanion undergoes supramolecular dimerization through charged polyarene stacking, wherein two molecules are linked at all three contact points. The preference for dimerization over dendrimerization is attributed to an entropic effect. The dimer is found to undergo complex structural dynamics, as well as ion-pairing dynamics, as revealed by variable-temperature 1 H- and 7 Li-NMR. Copyright © 2012 John Wiley & Sons, Ltd. Supporting information may be found in the online version of this paper. Keywords: anions; charged polyarene stacking; corannulene; nuclear magnetic resonance; oligocorannulenes; stereochemistry; supramolecular chemistry INTRODUCTION Buckybowls – curved polyarenes that can be mapped on fullerene surfaces – constitute an important class of carbon-rich compounds, exhibiting unique chemistry which arises from the interplay between aromatic stabilization and steric strain. [1–4] Corannulene (C 20 H 10 , 1, Fig. 1) is the smallest curved fragment of fullerene C 60 and the archetypal buckybowl. [5] The appealing properties of corannulene, which arise from its curvature and high symmetry, span across several branches of chemistry and include organometallic complexation by transition [6–8] and main group [9,10] metals, supramolecular self-assembly in the neu- tral, [11–14] anionic [15–18] and surface-bound states, [19,20] rapid structural dynamics of bowl-to-bowl inversion, [21,22] special 2D crystallization modes, [23–25] interesting photophysical proper- ties, [26–28] and rich redox chemistry. [29–32] Redox chemistry is a significant feature of corannulene in particular, and symmetric polyarenes in general (for which the latter are known as ‘ syn- thetic metals’). [4,33–35] Upon reduction, polyarenes might exhibit various transformations, such as reorganization of bonding patterns, [36–38] anisotropic distribution of charge, [39–41] and ring closure reactions. [42,43] Furthermore, some polyarene anions self-assemble into larger structures, by interactions of varying strength. These interactions range from covalent dimeriza- tions, [44,45] through coordinative binding by localized C–Li–C bonds, [46] to charged polyarene stacking, where non-localized p–M + –p bonds allow a layer of alkali metal cations (M + ) to ‘ glue’ together highly charged anionic decks. [15–18] In the particular case of corannulene, varying its charge between +2 and 4 causes drastic changes in ring currents. [47,48] Reduction of 1 leads to gradual flattening of the bowl, [32,49] and to supramolecular dimerization through charged polyarene stacking, when reduced by lithium metal to a tetraanion. [15,18] The self-assembly of corannulene tetraanion has recently been utilized as a construction mechanism leading to novel supramolecu- lar architectures (Fig. 2). [16,17,50] Based on this mechanism, we have demonstrated the formation of supramolecular polymers with two dicorannulenylic monomers: bicorannulenyl [17] and 1,4-dicorannule- nylbenzene [50] (Fig. 1, compounds 2 and 3, respectively). Employment of the corannulene unit for supramolecular poly- mer design necessitates the utilization of oligocorannulenes – polyarenes composed of several tethered corannulenyl units – as monomers. The chemistry of oligocorannulenes ranges from multiplication of the properties of corannulene (e.g. multiple occurrences of charged polyarene stacking) to novel phenomena which emerge from the interaction between the corannulenyl * Correspondence to: R. Shenhar, Institute of Chemistry and the Lise Meitner- Minerva Center for Computational Quantum Chemistry, The Hebrew Univer- sity of Jerusalem, Edmond J. Safra Campus, Jerusalem 91904, Israel. E-mail: roys@huji.ac.il **Correspondence to: L. T. Scott, Department of Chemistry, Merkert Chemistry Center, Boston College, Chestnut Hill, MA 02467, USA. E-mail: lawrence.scott@bc.edu a D. Eisenberg, R. Shenhar Institute of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Jerusalem 91904, Israel b J. M. Quimby, L. T. Scott Department of Chemistry, Merkert Chemistry Center, Boston College, Chestnut Hill, MA 02467, USA Research Article Received: 15 December 2011, Accepted: 30 March 2012, Published online in Wiley Online Library: 2012 (wileyonlinelibrary.com) DOI: 10.1002/poc.2951 J. Phys. Org. Chem. (2012) Copyright © 2012 John Wiley & Sons, Ltd.