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

Abstract

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.