Corannulene as a Lewis Base: Computational Modeling of Protonation and Lithium Cation Binding

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• 作者：Maxim V. Frash ; Alan C. Hopkinson ; and Diethard K. Bohme
• 刊名：Journal of the American Chemical Society
• 出版年：2001
• 出版时间：July 11, 2001
• 年：2001
• 卷：123
• 期：27
• 页码：6687 - 6695
• 全文大小：126K
• 年卷期：v.123,no.27(July 11, 2001)
• ISSN：1520-5126

文摘

A computational modeling of the protonation of corannulene at B3LYP/6-311G(d,p)//B3LYP/6-311G(d,p) and of the binding of lithium cations to corannulene at B3LYP/6-311G(d,p)//B3LYP/6-31G(d,p)has been performed. A proton attaches preferentially to one carbon atom, forming a -complex. The isomerprotonated at the innermost (hub) carbon has the best total energy. Protonation at the outermost (rim) carbonand at the intermediate (bridgehead rim) carbon is less favorable by ca. 2 and 14 kcal mol^-1, respectively.Hydrogen-bridged isomers are transition states between the -complexes; the corresponding activation energiesvary from 10 to 26 kcal mol^-1. With an empirical correction obtained from calculations on benzene, naphthalene,and azulene, the best estimate for the proton affinity of corannulene is 203 kcal mol^-1. The lithium cationpositions itself preferentially over a ring. There is a small energetic preference for the 6-ring over the 5-ringbinding (up to 2 kcal mol^-1) and of the convex face over the concave face (3-5 kcal mol^-1). The Li-bridgedcomplexes are transition states between the -face complexes. Movement of the Li⁺ cation over either face isfacile, and the activation energy does not exceed 6 kcal mol^-1 on the convex face and 2.2 kcal mol^-1 on theconcave face. In contrast, the transition of Li⁺ around the corannulene edge involves a high activation barrier(24 kcal mol^-1 with respect to the lowest energy -face complex). An easier concave/convex transformationand vice versa is the bowl-to-bowl inversion with an activation energy of 7-12 kcal mol^-1. The computedbinding energy of Li⁺ to corannulene is 44 kcal mol^-1. Calculations of the ⁷Li NMR chemical shifts andnuclear independent chemical shifts (NICS) have been performed to analyze the aromaticity of the corannulenerings and its changes upon protonation.