Coordination chemistry of buckybowls: from corannulene to a hemifullerene

Open-cage fullerenes as ligands for metals

The remarkable structures of open-cage fullerenes with functionalization on the outer surface and an accessible inner void make them interesting ligands for reactions with metal complexes. The behaviors of open-cage fullerenes in reactions with various metal complexes are examined and compared to the corresponding reactions with intact fullerenes. The structural results from X-ray diffraction are emphasized. Open-cage fullerenes frequently undergo unanticipated structural changes such as carbon-carbon bond cleavage upon reactions with metal complexes. Much more remains to be learned about the possibility of inserting metal ions larger than Li+ into the interior void of these open-cage fullerenes and about the effects of redox reactions on metal complexes of open-cage fullerenes.

Mechanochemical Synthesis of Corannulene: Scalable and Efficient Preparation of A Curved Polycyclic Aromatic Hydrocarbon under Ball Milling Conditions

Corannulene, a curved polycyclic aromatic hydrocarbon, is prepared in a multigram scale through mechanochemical synthesis. Initially, a mixer mill approach is examined and found to be suitable for a gram scale synthesis. For larger scales, planetary mills are used. For instance, 15 g of corannulene could be obtained in a single milling cycle with an isolated yield of 90 %. The yields are lower when the jar rotation rate is lower or higher than 400 revolutions per minute (rpm). Cumulatively, 98 g of corannulene is produced through the ball milling-based grinding techniques. These results indicate the future potential of mechanochemistry in the rational chemical synthesis of highly curved nanocarbons such as fullerenes and carbon nanotubes.

Catalytic effect of graphene on the inversion of corannulene using a continuum approach with the Lennard-Jones potential

The catalytic effect of graphene on the corannulene bowl-to-bowl inversion is confirmed in this paper using a pair-wise dispersion interaction model. In particular, a continuum approach together with the Lennard-Jones potential are adopted to determine the interaction energy between corannulene and graphene. These results are consistent with previous quantum chemical studies, which showed that a graphene sheet reduces the barrier height for the bowl-to-bowl inversion in corannulene. However, the results presented here demonstrate, for the first time, that the catalytic activity of graphene can be reproduced using pair-wise dispersion interactions alone. This demonstrates the major role that pair-wise dispersion interactions play in the catalytic activity of graphene.

Graphitic supramolecular architectures based on corannulene, fullerene, and beyond

In this Feature Article, we survey the advances made in the field of fulleretic materials over the last five years. Merging the intriguing characteristics of fulleretic molecules with hierarchical materials can lead to enhanced properties of the latter for applications in optoelectronic, biomaterial, and heterogeneous catalysis sectors. As there has been significant growth in the development of fullerene- and corannulene-containing materials, this article will focus on studies performed during the last five years exclusively, and highlight the recent trends in designing fulleretic compounds and understanding their properties, that has enriched the repertoire of carbon-rich functional materials.

Solid-Gas Phase Synthesis of Coordination Networks by Using Redox-Active Ligands and Elucidation of Their Oxidation Reaction

Formation of coordination networks is a complex process affected by a multitude of factors. Many synthetic strategies have been developed that attempt to control these factors and direct the structure of the final product. Coordination bond formation and structural assembly processes, however, typically take place either in the solution or solid states. In comparison, gas-phase network synthesis remains largely unexplored. Herein, two new two-dimensional coordination networks are obtained from the solid-gas phase reaction between ZnX₂ (X=I, Br) and the redox-active 2,5,8-tri(4-pyridyl)1,3-diazaphenalene (HTPDAP) ligand. Their structures were solved by ab initio powder X-ray diffraction analysis and feature a novel Zn halide trimeric cluster. This strategy is contrasted with a conventional solvothermal synthesis, which led to a one-dimensional coordination polymer instead. The intrinsic electroactive properties of these materials were probed by solid-state cyclic voltammetry measurements, which revealed the presence of HTPDAP and halide-based processes. Chemical oxidation of the two-dimensional networks by using NOPF₆ agent, unexpectedly, led to the formation of a nitrated analog of HTPDAP, the PF₆ ^- salt of diprotonated 4,6,7,9-tetranitro-2,5,8-tris(4-pyridyl)diazaphenalene cation (denoted N-TPDAP), which was isolated and characterized. These results provide deeper insights into the oxidation process of HTPDAP-containing networks and uncover unique redox-induced chemical transformations.

Synthesis of a sumanenyl hafnocene complex

A convex-bound sumanenyl hafnocene complex was selectively synthesized, and the catalytic activity of sumanenyl metallocenes was demonstrated in the carboalumination reaction.

From corannulene to larger carbon bowls: are they better for multiple metal encapsulation?

The effects of size, charge and symmetry of carbon π-bowls on their supramolecular assembly and metal ion intercalation trends are discussed.

Comprehensive Theoretical Study of Interactions between Ag+ and Polycyclic Aromatic Hydrocarbons

The first comprehensive and systematic theoretical exploration of the bonding nature and energetics of the interactions between Ag(I) cation and a wide set of π-ligands was accomplished. This set ranges from simple ethylene and aromatic benzene to planar and curved polyaromatic molecules and to closed-cage C₆₀ -fullerene. Simultaneous application of two energy decomposition schemes based on different ideas, namely, NBO-NEDA and EDA-NOCV, allowed shedding light on the nature of the bonding and its energetics. Importantly, our results unambiguously indicate that reliable results can be obtained only if using more than one theoretical approach. All methods clearly revealed the importance and even domination of the ionic contribution of the bonding in all adducts, except for those of C₆₀ -fullerene, in which the covalent component was found to be the largest. Subsequent decomposition of the orbital term onto components showed that it consists of two major parts: (i) ligand-to-metal (π(C=C)→s(Ag), L→M) and (ii) metal-to-ligand (M→L) terms, with significant domination of the former. Interestingly, while the L→M component is essentially the same for all systems considered, the nature of the M→L one depends on the coordination site of the polycyclic aromatic hydrocarbons (PAH). In most of adducts, the M→L can be described as d_xy (Ag)→π^* (C=C) donation, whereas for systems [Ag-spoke-C₁₂ H₈ ]⁺ and [Ag-spoke-C₂₀ H₁₀ ]⁺ it corresponds to the d_z ² (Ag)→π^* (C=C) type of interaction. As a result, the coordination mode in such complexes is switched from η² -type to η¹ . Thus, the nature of the bonding, its energetics and even coordination mode in adducts of unsaturated hydrocarbons with late transition metal cations should be considered as a function of many components, which primarily includes the topology and aromaticity of the (poly)aromatic molecules.

Bending Carbon Nanoforms for Supramolecular Recognition: A Topological Study on Hemifullerene-Based Aggregates

Buckybowls have risen as appealing fullerene fragment derivatives. Their intrinsic curvature has been exploited in the generation of host-guest supramolecular assemblies, not only through concave-convex complementarity but also through less-known concave-concave staggered arrangements. Whereas the stabilization of bowl-in-bowl dispositions has been ascribed to efficient π-π forces together with favorable dipole-dipole interactions, a detailed analysis on the forces guiding the formation of the staggered arrangements is missing so far. Herein, we present a thorough theoretical characterization of bowl-in-bowl vs staggered hemifullerene-based homodimers and heterodimers with the electron-donor truxTTF molecule, as test cases, under the density functional theory and by means of chemical bonding techniques. Our results clearly reveal strong and localized noncovalent signatures, together with an enhanced orbital interaction, associated with CH-π and sulfur-mediated interactions governing the staggered formation. Bending the fullerene fragment is demonstrated to favor the stabilization in both homo- and heterodimers, in good accord with the depletion in the π-electron density calculated upon increasing the buckybowl curvature. The optimal buckybowl curvature for the highest interaction energy is, however, dependent on the type of supramolecular assembly (bowl-in-bowl vs staggered) and the concave region to which hemifullerene approaches truxTTF. Interestingly, two regimes are found as a function of buckybowl curvature for hemifullerene homodimers: bowl-in-bowl dispositions are calculated more stable at low curvatures whereas staggered dimers prevail for highly curved buckybowls. Our results highlight the potential of discrete CH-π and sulfur-mediated interactions to generate unconventional staggered supramolecular arrangements toward the development of a new and unexplored host-guest chemistry.

Reactions of Dilithium Dibenzopentalenides with Cr(CO)3 (CH3 CN)3 : Unexpected Formation of a Cubic Tetramer of an Anionic Hydrodibenzopentalenyl Complex

To explore the coordination chemistry of dibenzopentalene dianion, reactions of two dilithium dibenzopentalenides having different silyl substituents with Cr(CO)₃ (CH₃ CN)₃ were investigated. The products were unexpected anionic complexes, [Li(Et₂ O)]⁺ [Cr(η⁵ -9-hydrodibenzopentalenyl)(CO)₃ ]^- . The proton at the 9-position is derived from Cr(CO)₃ (CH₃ CN)₃ , as evidenced by the use of Cr(CO)₃ (CD₃ CN)₃ . The X-ray diffraction analysis revealed that the chromium is coordinated by an anionic five-membered ring of the pentalene skeleton, and the lithium atom is coordinated by oxygen atoms of the carbonyl groups. The complexes form a dimer or a cage-like tetramer via carbonyl-lithium interactions, depending on the bulk of the silyl groups. The cubic tetramer appears to retain its cage structure in nonpolar solvents such as benzene.

Concave binding of cationic Li to quadrannulene

Concave binding of cationic Li to quadrannulene and its influence on buckybowl functionalization are introduced using DFT calculations.

Erecting buckybowls onto their edge: 2D self-assembly of terphenylcorannulene on the Cu(111) surface

A 2D self-assembly of a C₃₂H₁₂ buckybowl on the Cu(111) surface has been studied by means of scanning tunnelling microscopy. Additional aromatic rings at the rim of the corannulene core cause the bowl-shaped molecule to stand on its edge. This adsorption mode allows distinct π–π and C–H⋯π interactions between the convex bowl surfaces as well as between the hydrogen-terminated rim and the convex bowl faces.

Mixing Li and Cs in the reduction of corannulene for the assembly of a cesium-capped sandwich with a hexanuclear heterometallic core

In the first Li/Cs organometallic self-assembly, the tetrareduced corannulene decks are angled up to keep the highly-charged (Li₃Cs₃)⁶⁺ unit in between, with two external Cs⁺ ions capping the sandwich from outside.

Corannulene-Helicene Hybrids: Chiral π-Systems Comprising Both Bowl and Helical Motifs

Two distinct structural elements that render π-systems nonplanar, i.e., geodesic curvature and helical motifs, have been combined into new polyarenes that contain both features. The resultant corannulene-[n]helicenes (n = 5, 6) show unique molecular dynamics in their enantiomerization processes, including inversion motions of both the bowl and the helix. Optical resolution of a corannulene-based skeletally chiral molecule was also achieved for the first time, and the influence of the bowl-motif annulation on the chiroptical properties was investigated.

Buckybowls: Corannulene and Its Derivatives

Corannulene, a kind of bowl like polycyclic aromatic hydrocarbon (PAH), whose molecule is composed of a central pentagon and five closely adjacent hexagons on the pentagon's five sides, has received great scientific interest among research groups. In this review, the syntheses, characteristic molecule structure and properties of corannulene are clarified, as well as its derivatives with different substituted groups, fused derivatives, metal complex, and derivatives for host guest chemistry. On the basis of reviewing the applications and properties of corannulene together with its derivatives, the potential applications in hydrogen storage and lithium storage were highlighted and prospected.

Ion-π interaction in impacting the nonlinear optical properties of ion-buckybowl complexes

Ion-buckybowl complexes have received considerable attention in modern chemical research due to its fundamental and practical importance. Herein, we performed density functional theory (DFT) to calculate the geometical structure, binding interactions, dipole moments and the first hyperpolarizabilities (βtot) of ion-buckybowl complexes (ions are Cl(-) and Na(+), buckybowls are quadrannulene, corannulene and sumanene). It is found that the stabilities of ion-buckybowl compounds primarily originate from the interaction energy, which was proved by a new isomerization energy decomposition analysis approach. Plots of reduced density gradient mirror the ion-π weak interaction has been formed between the ions and buckybowls. Significantly, the buckybowl subunits cannot effectively impact the nonlinear optical (NLO), but the kind of ion has marked influence on the second-order NLO responses. The βtot values of Cl(-)-buckybowl complexes are all larger as compared to that of Na(+)-buckybowl complexes, which is attributed to the large charge-transfer (CT) from Cl(-) to buckybowl. Our present work will be beneficial for further theoretical and experimental studies on the NLO properties of ion-buckybowl compounds.

Electrochemically active porous organic polymers based on corannulene

For the first time, porous organic polymers (POPs) based on the smallest buckybowl, corannulene (BB-POPs) have been synthesized.

Regioselective Synthesis and Characterization of Multinuclear Convex-Bound Ruthenium-[n]Cycloparaphenylene (n = 5 and 6) Complexes

Mono- and multinuclear complexes of ruthenium and [n]cycloparaphenylene (CPP, n = 5 and 6) were synthesized in excellent yields through ligand exchange of the cationic complex [(Cp)Ru(CH3CN)3](PF6) with CPP. In the multinuclear complexes, ruthenium selectively coordinated to alternate paraphenylene units to give bis- and tris-coordinated Ru complexes for [5] and [6]CPPs, respectively. Single-crystal X-ray analysis revealed the Ru was coordinated with η(6)-hapticity on the convex surface of CPP.

Bowl inversion of surface-adsorbed sumanene

Bowl-shaped π-conjugated compounds offer the possibility to study curvature-dependent host-guest interactions and chemical reactivity in ideal model systems. For surface-adsorbed π bowls, however, only conformations with the bowl opening pointing away from the surface have been observed so far. Here we show for sumanene on Ag(111) that both bowl-up and bowl-down conformations can be stabilized. Analysis of the molecular layer as a function of coverage reveals an unprecedented structural phase transition involving a bowl inversion of one-third of the molecules. On the basis of scanning tunneling microscopy (STM) and complementary atomistic simulations, we develop a model that describes the observed phase transition in terms of a subtle interplay between inversion-dependent adsorption energies and intermolecular interactions. In addition, we explore the coexisting bowl-up and -down conformations with respect to host-guest binding of methane. STM reveals a clear energetic preference for methane binding to the concave face of sumanene.

Ring-annelated corannulenes as fullerene receptors. A DFT-D study

Ring-annelated corannulenes behave as better C₆₀/C₇₀ receptor than corannulene C₂₀H₁₀. The interaction is dominated by dispersion, with CH⋯π interactions playing a very important role.