Double-Concave Binding of Bicorannulenyl Dianion: Cesium vs Lithium Salts Natalie J. Sumner, † Sarah N. Spisak, † Alexander S. Filatov, † Andrey Yu. Rogachev, ‡ Alexander V. Zabula, § and Marina A. Petrukhina* ,† † Department of Chemistry, University at Albany, State University of New York, Albany, New York 12222, United States ‡ Department of Biological and Chemical Sciences, Illinois Institute of Technology, Chicago, Illinois 60616, United States § Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, United States * S Supporting Information ABSTRACT: The first X-ray structural characterization of bicorannulenyl dianion has been accomplished for two alkali metal salts, [Li + (THF) 4 ] 2 [C 40 H 18 2- ] (1) and [Cs + (18-crown-6)] 2 [C 40 H 18 2- ] (2). This crystallographic study revealed the biaryl stereochemistry, geometry transformation upon acquiring two electrons, and different binding preferences of Li + vs Cs + ions in the solid-state products. T he design and synthesis of extended π-systems utilizing bowl-shaped polyarenes as functional building units has become a new research direction in recent years. 1,2 Varying the length and nature of the linkage between the curved fragments is effectively used to alter the electronic coupling and supramolecular oligomerization behavior, giving rise to new properties and interesting applications of the resulting carbon- rich compounds. The small bowl-shaped polyarene corannu- lene (C 20 H 10 ) is commonly used for such applications due to its availability based on the well-developed preparation methods. 3 Using corannulene pincers, remarkable molecular receptors have been prepared with unique molecular recognition toward fullerene binding based on complementary convex-concave π-π stacking interactions. 4 Fusion of corannulene units to anion-responsive π-conjugated molecules afforded novel self- organized molecular materials with enhanced charge carrier mobility. 5 Self-assembly of π-bowls coupled with redox-active organometallic spacers in corannulenylferrocenes and suma- neylferrocenes has also been explored. 6 Direct aryl-aryl coupling of two corannulene bowls affords bicorannulenyl (C 40 H 18 , Scheme 1), which exhibits a novel chirality and unique dynamic stereochemistry elucidated by Shenhar’s group using variable-temperature NMR spectroscopy and DFT calculations. 7 Recently, such isomerism was also found by Hirao and co-workers for bisumanenyl, having two linked sumanene (C 21 H 12 ) bowls. 8 The redox properties of such extended aromatic systems composed of coupled bowl- shaped fragments, known to be excellent individual reservoirs for multiple electrons, 9 are especially interesting. 10 The reduction of bicorannulenyl has been previously investigated using solution NMR spectroscopy augmented by DFT calculations. 11 The in-depth investigation of the stereodynamics of bicorannulenyl dianion revealed 13 stable conformations: six pairs of enantiomers and a single achiral isomer (PM 180 ). Such flexibility led to problems with unequivocal interpretation of NMR data for the in situ formed bicorannulenyl dianion. While there are three stable diastereomers that are more energetically favorable, the PM 180 isomer was proposed to be the major species existing in solution. On the basis of the bond-order considerations, it was also predicted that the single bond tethering two corannulene units in bicorannulenyl should gain substantial double-bond character upon acquisition of two electrons, converting it to a charged overcrowded ethylene (Scheme 1). 11 Until now, no solid-state products of charged bicorannulenyl have been reported to give further insights on the stereochemistry and geometry transformation of C 40 H 18 upon acquiring extra electrons. In this work, we targeted the isolation of crystalline products of bicorannulenyl dianion in order to perform its first crystallographic investigation and to evaluate its metal-binding properties. We selected lithium and cesium for this study, as these two alkali metals show distinctly different binding preferences toward corannulene anions. While lithium ions Received: April 14, 2014 Published: May 21, 2014 Scheme 1. Transformation of Bicorannulenyl upon Reduction to Dianion Article pubs.acs.org/Organometallics © 2014 American Chemical Society 2874 dx.doi.org/10.1021/om500396m | Organometallics 2014, 33, 2874-2878