How Charging Corannulene with One and Two Electrons Affects Its Geometry and Aggregation with Sodium and Potassium Cations

• Published in: Chemistry : a European journal Vol. 18; no. 21; pp. 6476 - 6484
• Main Authors: Zabula, Alexander V., Spisak, Sarah N., Filatov, Alexander S., Grigoryants, Vladimir M., Petrukhina, Marina A.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 21.05.2012; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: alkali metals; Anions; carbanions; Chemistry; corannulene; Diffraction; Ethers; molecular structure; Perturbation; Potassium; Single crystals; Sodium; X-ray diffraction; X-rays
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201200416

Bowl‐shaped mono‐ and dianions are prepared by reduction of corannulene (C20H10, 1) with sodium and potassium metals in the presence of [18]crown‐6 ether. Single‐crystal X‐ray diffraction studies of two sodium salts, [Na(THF)2([18]crown‐6)]+[1−] (2 a) and [Na([18]crown‐6)]+[1−] (2 b), reveal the presence of naked corannulene monoanions 1− in both cases. In contrast, the potassium adduct, [K([18]crown‐6)]+[1−] (3), shows an η2‐binding of the K+ ion to the convex face of 1−. For the first time, corannulene dianions have been isolated as salts with sodium, [Na2([18]crown‐6)]2+[12−] (4 a) and [Na(THF)2([18]crown‐6)]+[Na([18]crown‐6)]+[12−] (4 b), and potassium counterions, [K([18]crown‐6)]2+[12−] (5). Their structural characterization reveals geometry perturbations upon addition of two electrons to a bowl‐shaped polyarene. It also demonstrates η5‐ or η6‐binding of metals to the curved carbon surface of 12−, depending on the crystallization conditions. Both mono‐ and doubly‐charged corannulene bowls show the preferential exo binding of Na+ and K+ ions in all investigated compounds. Various types of CH⋅⋅⋅π interactions are found in the crystals of 2–5. The UV/Vis, ESR, and 1H NMR spectroscopic studies of 2–5 indicate different coordination environment of corannulene anions in solution, depending on the metal ion. Adding metals to a bowl: Mono‐ and dianions of corannulene have been isolated in the form of their salts with sodium and potassium ions in the presence of [18]crown‐6 ether. Single‐crystal X‐ray diffraction studies reveal the geometrical perturbations of the corannulene core upon stepwise electron acquisition and various metal‐ion binding modes. UV/Vis, ESR, and NMR spectroscopy investigations demonstrate different environments of the bowl‐shaped anions in solution (see figure).