Systematic Inflation of Buckminsterfillerene C60: Synthesis of Diphenyl Fulleroids C61 to C66

High-symmetry cage-like molecule N20(C2B2)30: computational insight into its bonding and reactivity

On the basis of density functional theory (DFT) calculations and AIMD simulations, a novel Ih-symmetry cage-like molecule N20(C2B2)30 is constructed and characterized computationally. It is found that N20(C2B2)30 is structurally similar to fullerene C20, but it has high thermodynamic and kinetic stability. The designed N20(C2B2)30 exhibits strong chemical reactivities, including reactivities for the Diels-Alder reaction with butadiene (C4H6) and cyclopentadiene (C5H6), as well as for the [3+2] addition reaction with diazomethane (N2CH2). In addition, the presence of the boron site and the inverted CC bond with the charge-shift (CS) bonding in N20(C2B2)30 make it quite active not only for cycloaddition reactions but also for capture of small molecules (e.g. H2, CO, NO, and NO2). Once N20(C2B2)30 complexes with a transition metal (TM) ion, the resultant complexes (TM)N20(C2B2)30+ (TM = Cu, Ag, and Au) can bind inactive CO2 and N2O at the TM site. Furthermore, AuN20(C2B2)30+ is able to effectively separate CO2 and N2O. Owing to its unique porous structure and reactivity as well as high stability, N20(C2B2)30 may further enrich the diversity of a highly symmetrical molecular family.

C2-insertion into a fullerene orifice

The embedment of a C_n-unit into a carbon network constituting fullerene(s) potentially enables a cage-expansion. Herein, we report a C2-insertion into a fullerene orifice in which the mechanism was examined computationally. The C2-embedded open-[60]fullerene possesses an orifice enlarged from an octagon to a decagon, while the inner space was notably expanded as confirmed by the dynamic motion of the incarcerated H₂O molecule.

Synthesis of [60]- and [70]Fullerene-Fused Tetrahydroquinoxaline Derivatives by Oxidative [4 + 2] Cycloaddition with Unusual Reactivity and Regioselectivity

The oxidative [4 + 2] reaction of o-phenylenediamine-derived disulfonamides with fullerene C₆₀ and C₇₀ is reported, in which electron-deficient reactants showed high reactivity. The reaction of C₇₀ exhibited unusual regioselectivity, yielding a [5,6]-adduct as the major product, which was characterized by ¹H, ¹³C NMR and single-crystal X-ray diffraction. DFT calculations revealed the reaction is an inverse-electron-demand Diels-Alder (IEDDA) reaction, and the [5,6]-adduct of C₇₀ is a kinetic product.

Shape Entropy of a Reconfigurable Ising Surface

Disclinations in a 2D sheet create regions of Gaussian curvature whose inversion produces a reconfigurable surface with many distinct metastable shapes, as shown by molecular dynamics of a disclinated graphene monolayer. This material has a near-Gaussian "density of shapes" and an effectively antiferromagnetic interaction between adjacent cones. A∼10  nm patch has hundreds of distinct metastable shapes with tunable stability and topography on the size scale of biomolecules. As every conical disclination provides an Ising-like degree of freedom, we call this technique "Isigami."

Cage-Expansion of Fullerenes

Despite the first proposal on the cage inflation of fullerenes in 1991, the chemical expansion of fullerenes has been still a formidable challenge. Herein, we provide an efficient methodology to expand [60] and [70]fullerene cages by the inclusion of totally C5N unit, giving nitrogen-containing closed structures as C₆₅N and C₇₅N with double fused heptagons. This method consists of two steps commenced with the construction of an opening by the reaction with triazine as a C3N source, followed by the cage reformation using N-phenylmaleimide as a C2 source. We also synthesized endohedral cages, demonstrating that the encapsulated H₂O molecule inside the C₇₅N cage prefers the orientation which maximizes the intramolecular interaction with the carbon wall. Additionally, we revealed the existence of a through-space magnetic dipolar interaction between the encapsulated H₂ molecule and the embedded N atom.

[2 + 1] Cycloaddition reactions of fullerene C60 based on diazo compounds

The most common variant of fullerene core functionalization is the [2 + 1] cycloaddition process. Of these, reactions leading to methanofullerenes are the most promising. They are synthesized in two main reactions: nucleophilic cyclopropanation according to the Bingel method and thermal addition of diazo compounds. This present review summarizes the material on the synthesis of monofunctionalized methanofullerenes - analogues of [60]PCBM - based on various diazo compounds. The main cyclopropanating agents for the synthesis of monosubstituted methanofullerenes, the optimal conditions and the mechanism of the [2 + 1] cycloaddition, as well as the practical application of the target products are analyzed.

Bingel-Hirsch Addition of Diethyl Bromomalonate to Ion-Encapsulated Fullerenes M@C60 (M=Ø, Li+, Na+, K+, Mg2+, Ca2+, and Cl-)

In the last 30 years, fullerene-based materials have become popular building blocks for devices with a broad range of applications. Among fullerene derivatives, endohedral metallofullerenes (EMFs, M@C_x) have been widely studied owing to their unique properties and reactivity. For real applications, fullerenes and EMFs must be exohedrally functionalized. It has been shown that encapsulated metal cations facilitate the Diels-Alder reaction in fullerenes. Herein, the Bingel-Hirsch (BH) addition of ethyl bromomalonate over a series of ion-encapsulated M@C₆₀ (M=Ø, Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, and Cl^-; Ø@C₆₀ stands for C₆₀ without any endohedral metal) is quantum mechanically explored to analyze the effect of these ions on the BH addition. The results show that the incarcerated ion has a very important effect on the kinetics and thermodynamics of this reaction. Among the systems studied, K⁺@C₆₀ is the one that leads to the fastest BH reaction, whereas the slowest reaction is given by Cl^-@C₆₀.

Crystallographic Structure Determination of Both [5,6]- and [6,6]-Isomers of Lithium-Ion-Containing Diphenylmethano[60]fullerene

Organic functionalization of lithium-ion-containing [60]fullerene, Li⁺@C₆₀, was performed by using diphenyl(diazo)methane as a stable, readily available diazo compound to obtain lithium-ion-containing [5,6]- and [6,6]-diphenylmethano[60]fullerenes, Li⁺@C₆₁Ph₂. The bis(trifluoromethanesulfonyl)imide (TFSI) salts of [5,6]- and [6,6]-Li⁺@C₆₁Ph₂ were successfully separated by using a cation exchange column with eluent containing LiTFSI. Improved separation protocol and high crystallinity of ionic components in less polar solvents enabled separate crystallization of each isomer. Both [5,6]-open and [6,6]-closed structures of Li⁺@C₆₁Ph₂ were determined by synchrotron radiation X-ray crystallography. Elucidating the [5,6]-open methano[60]fullerene (fulleroid) structure will contribute to materials research on fulleroids.

Synthesis, the electronic properties and efficient photoinduced electron transfer of new pyrrolidine[60]fullerene- and isoxazoline[60]fullerene-BODIPY dyads: nitrile oxide cycloaddition under mild conditions using PIFA

The first synthesis of fulleroisoxazoline-BODIPY whose electron-accepting ability of the C₆₀ cage is better than its fulleropyrrolidine-BODIPY counterpart.

Synthesis of homoazafullerene [C59N(CH2)]R and azahomoazafullerene [C59N(NH)]R

The selective insertion of a CH₂ or NH group is achieved through the PCl₅ induced reaction of a CH₂OH or NHOH group, respectively.

Regioselective Diels–Alder reaction to open-cage ketolactam derivatives of C60

Open-cage ketolactam fullerenes reacted with dienes on the rim of the orifice both regio- and endo-selectively, which were confirmed by 2D INADEQUATE ¹³C NMR of ¹³C enriched material/HMBC spectra as well as the theoretical calculations.

Synthesis of a Novel C60-Containing Polyimide: A New ‘Charm-Bracelet’ Type of Polyimide and Copolyimide

The fullerene-containing polyimides were synthesized by the reaction of diamines and C60-containing dianhydride 2 and copolyimides were synthesized by the reaction of 2, 4, 4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 4, 4′-diaminodiphenyl ether (ODA). Polyamic acids 3a, b and copolyamic acids 8b–e were soluble in polar aprotic solvents such as DMAc, DMF, DMSO and NMP, whereas 8b–e showed additional solubility in THF. The molecular weights of polyamic acids 3a, b and copolyimides 9b−e determined by gel permeation chromatography were in the range of 1.0 × 10 4−7.8 × 103 and 5 × 104−2.8 × 104 mol g−1, respectively. Polyamic acid 3a ;b contained other lower molecular weight oligomers. TGA results for polyimides and copolyimides showed thermal stability and the 10% weight loss temperatures were in the range of 430–520 °. Distinct glass transition temperatures of C 6′-containing polyimides were not observed by DSC measurement. The cyclic voltammograms of 2 and 3a indicated four reduction waves corresponding to C60 redox reactions, but the polyamic acid 8e showed one reduction wave at −1.39 V.

The performance of selected semi-empirical and DFT methods in studying C₆₀ fullerene derivatives

The capability of reproducing the open circuit voltages (V(oc)) of 15 representative C60 fullerene derivatives was tested using the selected quantum mechanical methods (B3LYP, PM6, and PM7) together with the two one-electron basis sets. Certain theoretical treatments (e.g. PM6) were found to be satisfactory for preliminary estimates of the open circuit voltages (V(oc)), whereas the use of the B3LYP/6-31G(d) approach has been proven to assure highly accurate results. We also examined the structural similarity of 19 fullerene derivatives by employing principle component analysis (PCA). In order to express the structural features of the studied compounds we used molecular descriptors calculated with semi-empirical (PM6 and PM7) and density functional (B3LYP/6-31G(d)) methods separately. In performing PCA, we noticed that semi-empirical methods (i.e. PM6 and PM7) seem satisfactory for molecules, in which one can distinguish the aromatic and the aliphatic parts in the cyclopropane ring of PCBM (phenyl-C61-buteric acid methyl ester) and they significantly overestimate the energy of the highest occupied molecular orbital (E(HOMO)). The use of the B3LYP functional, however, is recommended for studying methanofullerenes, which closely resemble the structure of PCBM, and for their modifications.

Mechanochemistry of fullerenes and related materials

The low or lack of solubility of fullerenes, carbon nanotubes and graphene/graphite in organic solvents and water severely hampers the study of their chemical functionalizations and practical applications. Covalent and noncovalent functionalizations of fullerenes and related materials via mechanochemistry seem appealing to tackle these problems. In this review article, we provide a comprehensive coverage on the mechanochemical reactions of fullerenes, carbon nanotubes and graphite, including dimerizations and trimerizations, nucleophilic additions, 1,3-dipolar cycloadditions, Diels-Alder reactions, [2 + 1] cycloadditions of carbenes and nitrenes, radical additions, oxidations, etc. It is intriguing to find that some reactions of fullerenes can only proceed under solvent-free conditions or undergo different reaction pathways from those of the liquid-phase counterparts to generate completely different products. We also present the application of the mechanical milling technique to complex formation, nanocomposite formation and enhanced hydrogen storage of carbon-related materials.

Carbon-based layer-by-layer nanostructures: from films to hollow capsules

Over the past years, the layer-by-layer (LbL) assembly has been widely developed as one of the most powerful techniques to prepare multifunctional films with desired functions, structures and morphologies because of its versatility in the process steps in both material and substrate choices. Among various functional nanoscale objects, carbon-based nanomaterials, such as carbon nanotubes and graphene sheets, are promising candidates for emerging science and technology with their unique physical, chemical, and mechanical properties. In particular, carbon-based functional multilayer coatings based on the LbL assembly are currently being actively pursued as conducting electrodes, batteries, solar cells, supercapacitors, fuel cells and sensor applications. In this article, we give an overview on the use of carbon materials in nanostructured films and capsules prepared by the LbL assembly with the aim of unraveling the unique features and their applications of carbon multilayers prepared by the LbL assembly.

Preparation of open-cage fullerenes and incorporation of small molecules through their orifices

Open-cage fullerenes can act as hosts for small molecules such as water, nitrogen, or hydrogen, forming endohedral fullerenes. Following a brief summary of carbon, nitrogen, and oxygen insertion in the fullerene framework to form homofullerenes, methods of creating a hole in the fullerene surface are surveyed. Techniques of hole enlargement and the insertion of atoms or molecules through the orifice to form endohedral fullerenes are described. Finally, the possibility of subsequent closure of the hole is considered.

Stereoelectronic Effects in Diastereoselective Formation of Fulleroids

The substituent effects on diastereoselective formation of fulleroids in the reactions of C(60) with various unsymmetrical diazoalkanes were investigated. The steric demand on the stereochemical course of reactions dominated the diastereoselectivity for diazoalkanes bearing aliphatic as well as monosubstituted pi-resonating groups, whereas the stereoelectronic effects of coexisting pi-resonating aromatic and cyclopropyl groups played a crucial role in the ring closure of the radical intermediates, overriding the steric demand.