We have demonstrated the features of curve-structured phenalenyl chemistry, for the first time. A phenalenyl-fused corannulene anion has been designed by the annelation of a six-memberd ring across peri-positions of corannulene and generated as a stable species in a degassed solution. The 1H and 13C NMR spectra have shown the highly symmetrical structure and high-field shifts of protons and carbons at the asterisked positions in the chemical structure, indicating the occurrence of large negative charge densities at these positions. These results well agree with the HOMO picture and the electrostatic potential surface, demonstrating the phenalenyl anion-type electronic structure is retained in the curved-surface pi-system. The calculated bowl-inversion barrier of the anion (11.3 kcal/mol) is larger than that of corannulene (9.2 kcal/mol) because of peri-annelation of the corannulene skeleton. The calculations of the barriers of the neutral radical (12.6 kcal/mol), radical dianion (8.1 kcal/mol), and trianion (5.4 kcal/mol) of the phenalenyl-fused corannulene have exhibited a stepwise flattening of the curvature with increase in negative charge. Therefore, we have revealed that the bowl-inversion barrier of the anion is governed by the setoff of the peri-annelation and negative charge effects.

Organic radical ions play increasingly important roles in a wide range of research fields from biochemistry to materials science.[1] o-Semiquinone is a typical organic radical anion with multistage redox ability that can form chelate salts and complexes with many kinds of metal cations. Investigation of a variety of transition-metal complexes of o-semiquinone radical could help not only to increase general knowledge of their fundamental chemistry but also to develop functional materials based on valence tautomerism phenomena. [2,3] In contrast, the alkali-metal salts have been extensively studied, and much attention has been focused on the dynamic behavior of their structure and of the electronic features of the ion pair in solution. [4,5] Solution-phase ESR spectroscopy measurements of some alkali-metal salts show significant temperature dependence in their hyperfine coupling constants (hfccs). [4b,d] The origin of this behavior has been only qualitatively interpreted as temperature-dependent positional change or migration of the alkali-metal cation to the oxygen atoms of the o-semiquinone radical.[4e,h] A quantitative discussion of such dynamic behavior has not been carried out to date.Recently, we synthesized and isolated corannulene (1) [6] -based stable neutral mono-and diradical derivatives with bowl-shaped non-alternant p-conjugated systems.[7] Their three-dimensional spin-delocalized nature and intra-and intermolecular magnetic interactions were experimentally illustrated in terms of geometrical and topological aspects. These studies have inspired us to design a novel bowl-shaped radical anion system 2C À based on corannulene with the osemiquinone moiety. Notably, 2C À is the first bowl-shaped semiquinone radical anion with non-alternant p conjugation.[8] Herein we report the synthesis of a sodium salt of 2C, which is stable in an oxygen-free solution and even in the solid state under nitrogen atmosphere. Thanks to the high stability imparted by the bulky tert-butyl groups, we could evaluate 3D molecular and electronic structures of Na + ·2C À using the curvature and electronic spin and charge distribution by ESR spectroscopy and 1 H and 23 Na ENDOR/ TRIPLE measurements as well as by DFT calculations. We emphasize that the temperature dependence of the hfccs, related to the bowl-shaped structure, can for the first time allow for a quantitative discussion of the dynamic behavior of the ion pair in a solution of Na + ·2C À with the help of sophisticated DFT calculations. These studies demonstrate the salient structural and electronic features of a bowl-shaped semiquinone radical salt with the temperature-dependent positional change of a countercation, which originates in the concave-convex dynamics of the bowl-shaped skeleton.A synthetic route for Na + ·2C À is depicted in Scheme 1. Our modified experimental conditions of the reported penta-tertbutylation of 1 [9] gave tetra-tert-butyl corannulene 3 as the major product. By bromination and subsequent coupling reaction, [10] we obtained the silyl ether der...

A new corannulene-based curved neutral π-radical bearing a tert-butylnitroxide moiety has been synthesized and isolated as an air-stable solid. Direct attachment of the spin centre to the corannulene skeleton gives rise to an extensive spin-delocalization onto the curved π-conjugated system from the nitroxide moiety. This salient electronic feature in the curved neutral radical system and its high stability have allowed us to find a dynamic electronic-spin behaviour induced by the temperature-dependent conformational change of the nitroxide moiety, as studied by liquid-phase variable-temperature electron spin resonance and 1H electron-nuclear double resonance and electron-nuclear-nuclear triple resonance spectroscopies with the help of density functional theory calculations.

Organic radical ions play increasingly important roles in a wide range of research fields from biochemistry to materials science. [1] o-Semiquinone is a typical organic radical anion with multistage redox ability that can form chelate salts and complexes with many kinds of metal cations. Investigation of a variety of transition-metal complexes of o-semiquinone radical could help not only to increase general knowledge of their fundamental chemistry but also to develop functional materials based on valence tautomerism phenomena. [2,3] In contrast, the alkali-metal salts have been extensively studied, and much attention has been focused on the dynamic behavior of their structure and of the electronic features of the ion pair in solution. [4,5] Solution-phase ESR spectroscopy measurements of some alkali-metal salts show significant temperature dependence in their hyperfine coupling constants (hfccs). [4b,d] The origin of this behavior has been only qualitatively interpreted as temperature-dependent positional change or migration of the alkali-metal cation to the oxygen atoms of the o-semiquinone radical. [4e,h] A quantitative discussion of such dynamic behavior has not been carried out to date.Recently, we synthesized and isolated corannulene (1) [6] based stable neutral mono-and diradical derivatives with bowl-shaped non-alternant p-conjugated systems. [7] Their three-dimensional spin-delocalized nature and intra-and intermolecular magnetic interactions were experimentally illustrated in terms of geometrical and topological aspects. These studies have inspired us to design a novel bowl-shaped radical anion system 2C À based on corannulene with the osemiquinone moiety. Notably, 2C À is the first bowl-shaped semiquinone radical anion with non-alternant p conjugation. [8] Herein we report the synthesis of a sodium salt of 2C À (Na + ·2C À ), which is stable in an oxygen-free solution and even in the solid state under nitrogen atmosphere. Thanks to the high stability imparted by the bulky tert-butyl groups, we could evaluate 3D molecular and electronic structures of Na + ·2C À using the curvature and electronic spin and charge distribution by ESR spectroscopy and 1 H and 23 Na ENDOR/ TRIPLE measurements as well as by DFT calculations. We emphasize that the temperature dependence of the hfccs, related to the bowl-shaped structure, can for the first time allow for a quantitative discussion of the dynamic behavior of the ion pair in a solution of Na + ·2C À with the help of sophisticated DFT calculations. These studies demonstrate the salient structural and electronic features of a bowl-shaped semiquinone radical salt with the temperature-dependent positional change of a countercation, which originates in the concave-convex dynamics of the bowl-shaped skeleton.A synthetic route for Na + ·2C À is depicted in Scheme 1. Our modified experimental conditions of the reported penta-tertbutylation of 1 [9] gave tetra-tert-butyl corannulene 3 as the major product. By bromination and subsequent coupling reaction, [10] we obtained ...