A Hydrogen‐Bonded Hexagonal Buckybowl Framework

A hydrogen‐bonded two‐dimensionally networked buckybowl architecture is presented. Two types of hexagonal network (HexNet) structures ( CPSM‐1 and CPSM‐2 ) have been achieved based on a sumanene derivative ( CPSM ) possessing 4,4′‐dicarboxy‐o ‐terphenyl groups in the periphery. CPSM‐1 has a waved HexNet structure with an alternate alignment of upward and downward bowls. CPSM‐2 has a bilayered HexNet structure composed of hamburger‐shaped dimers of the bowls. This demonstrates that non‐planar π‐systems can be networked two‐dimensionally by an appropriate supramolecular synthon to achieve structurally well‐defined unique bumpy π‐sheets. Furthermore, we revealed that CPSM‐2 undergoes anisotropic shrinking along the c axis by 11 % under high pressure conditions (970 MPa). The shrinkage is brought about by offset sliding between bumpy π‐surfaces of the bilayered HexNet sheets.     

A computational study of cation-π interactions in polycyclic systems: exploring the dependence on the curvature and electronic factors

Density functional theory (B3LYP) calculations with double and triple-ζ quality basis sets were performed on the Li⁺ and Na⁺ π-complexes of corannulene 2, sumanene 3CH₂, heterosumanenes 3X, triphenylene 4 and heterotrindenes 5X. The metal ions bind to both convex and concave faces of buckybowls, with a consistent preference to bind to the convex surface by about 1-4 kcal/mol. The metal ion complexation with the π-framework of the central six-membered ring span wider range compared to benzene, indicating the control of size, curvature and electronic perturbations over the strength of cation-π interactions. Computations show that the bowl-to-bowl inversion barriers are only slightly altered upon metal complexation, indicating the continuity of bowl-to-bowl inversion despite metal complexation. We have calculated the binding energies of model systems, triphenylene (4) and heterotrindenes (5X), which indicate that the interaction energies are controlled by electronic factors. While the inversion barrier is dependent mainly on the size of the heteroatom, the extent of binding is independent of the size of the atom or the bowl depth.     

Bowl Inversion in an Exo‐type Supramolecule in the Solid State

Bowl inversion is a unique property of buckybowls. The polarity and assembly configuration of buckybowls are reversed after bowl inversion. So far, this unique phenomenon has been studied in solution and on surface, but not in solid state due to spatial constraint. Now a series of exo‐type supramolecular assemblies of trithiasumanene and nanographene are investigated. Tuning the electron density of the nanogaphene component was found to directly affect the binding constant of the complex. Reversible bowl inversion in the solid state was then successfully achieved by subjecting the trithiasumanene–nanographene assembly with the weakest binding strength to repeated heating–cooling cycles, which was unambiguously observed by single crystal X‐ray diffraction.     

Stepwise Reduction of Azapentabenzocorannulene

Mono‐ and dianions of 2‐tert‐butyl‐3a²‐azapentabenzo[bc,ef,hi,kl,no]corannulene ( 1 a ) were synthesized by chemical reduction with sodium and cesium metals, and crystallized as the corresponding salts in the presence of 18‐crown‐6 ether. X‐ray diffraction analysis of the sodium salt, [{Na⁺(18‐crown‐6)(THF)₂}₃{Na⁺(18‐crown‐6)(THF)}( 1 a ^2?)₂], revealed the presence of a naked dianion. In contrast, controlled reaction of 1 a with Cs allowed the isolation of singly and doubly reduced forms of 1 a , both forming π‐complexes with cesium ions in the solid state. In [{Cs⁺(18‐crown‐6)}( 1 a ^?)]?THF, asymmetric binding of the Cs⁺ ion to the concave surface of 1 a ^? is observed, whereas in [{Cs⁺(18‐crown‐6)}₂( 1 a ^2?)], two Cs⁺ ions bind to both the concave and convex surfaces of the dianion. The present study provides the first successful isolation and characterization of the reduced products of heteroatom‐containing buckybowl molecules.     

Barrelene-semibullvalene rearrangement induced by visible light: synthesis of dicorannulenosemibullvalene dimethyl dicarboxylate

A clean, quick conversion of biscorrannulenobarrelene dicarboxylate to the respective semibullvalene is observed upon irradiation of solutions of the former with a sun lamp. This represents the first reported example of such rearrangement induced by visible light. Hybrid density functional theory calculations predict the exo-endo conformer of the semibullvalene as the most stable, with the bis-exo and bis-endo conformers being higher in energy by ca. 1 and 4 kcal/mol, respectively.     

Palladium π-adduct of corannulene

The ternary palladium π-adduct of corannulene and benzene, [Pd₆Cl₁₂·(C₂₀H₁₀)₂·(C₆H₆)₂]·C₆H₆ (1), has been prepared by reacting the cubic Pd₆Cl₁₂-cluster with C₂₀H₁₀ in benzene. It was structurally characterized to reveal η¹-binding of Pd₆Cl₁₂ to a hub C-atom of the convex surface of corannulene (Pd?C, 3.085(3) Å) and its η⁶-complexation to benzene (Pd?C_centroid, 3.431(3) Å). The behavior and persistence of 1 in some aromatic solvents has been revealed by UV-vis and ¹H NMR spectroscopy studies.     

A Hybrid of Corannulene and Azacorannulene: Synthesis of a Highly Curved Nitrogen‐Containing Buckybowl

A highly curved nitrogen‐containing buckybowl, which can be considered as a corannulene/azacorannulene hybrid, was synthesized and characterized. This molecule has a polycyclic aromatic C₄₀N core, corresponding to a partial azafullerene structure C_80−xN_x (x=1,2,3…), and exhibits interesting properties that arise from its large and highly curved π surface and the embedded nitrogen atom, which include association with C₆₀, a lower LUMO level relative to azapentabenzocorannulene, and the formation of a radical cationic species upon oxidation.