Cage-Expansion of Fullerenes

Chiroptical Response of Carbon Nanocages Enhanced by Achiral Guests

Opening up [60]fullerene makes itself inherently chiral without loss of congenital π-conjugation. An immoderately large aperture on [60]fullerene, however, renders the molecule less rigid and therefore it would reduce dissymmetry factors. Herein, we examined supramolecular technique in geometrical reinforcement of chiral open-[60]fullerenes by encasing achiral guests such as Ar, CO2, and CH3CN. At a lowest-energy transition, we confirmed a guest-dependency on chiroptical responses with increasing a dissymmetry factor by nearly twice to three times. It should be noted that the guests play a negligible role in electronic structures of the carbon cages. Instead, they are engaged in preclusion of an orifice shrinking not to reduce chiroptical response.

NHC-BH2-C60H: synthesis, characterization and electrochemical properties of the N-heterocyclic-carbene-stabilized fullerene-borane complex

NHC-[60]fullereborane (NHC-BH2-C60H) has been synthesized, isolated in pure form, and characterized. The reaction of C60 with NHC-borane produced NHC-BH2-C60H as the first air-stable and separatable fullerene-borane compound. The formation of a N-heterocyclic carbene stabilized this borane complex of C60, and the structure of the complex was unambiguously determined throughsingle-crystal X-ray analysis. This fullerene-borane complex exhibited remarkable stability and promising electrochemical properties.

Direct Through-Space Substituent-π Interactions in Noncovalent Arene-Fullerene Assemblies

The arene-arene interactions between electron-rich and deficient aromatics have been less understood. Herein, we focus on a [60]fullerene π-surface as an electron-deficient aromatics. Using a 1H signal of H2O@C60 as a magnetic probe, the presence of benzene-fullerene interactions was confirmed. To investigate substituent effects on the noncovalent arene-fullerene interactions, NMR titration experiments were carried out using an open-[60]fullerene and a series of substituted benzenes, i. e., PhX (X=NO2, CN, Cl, OMe, H, CH3, and NH2), demonstrating a 1 : 2 stoichiometry with a positive correlation between stabilization energies upon the first association (ΔG1) and Hammet constants (σm). The destabilization of the self-assembled structure for X=OMe with a σ-withdrawing nature clearly showed direct through-space substituent-π interactions describable by the Wheeler-Houk model while the second association was suggested to be considerably perturbed by the secondary effects.

Carboxyfullerene C60 preserves porcine sperm by enhancing antioxidant capacity and inhibiting apoptosis and harmful bacteria

This study used a porcine model to systematically investigate whether carboxyfullerene C60(CF-C60) can be used for sperm preservation. The results indicated that CF-C60 supplementation can preserve porcine sperm quality during storage at 17 °C. This effect was attributable to an improvement in the antioxidant capacity of sperm through a decrease in the reactive oxygen species (ROS) level. Additionally, CF-C60 can maintain mitochondrial function, inhibit sperm apoptosis through the ROS/Cytochrome C (Cyt C)/Caspase 3 signaling pathway, and mediate suppression of bacterial growth through the effects of ROS. Finally, the results of artificial insemination experiments indicated that insemination with CF-C60-treated sperm can increase the total number of offspring born and reduce the number of deformed piglets. Thus, CF-C60 is safe for use as a component of semen diluent for sperm storage.

Recent advances in supramolecular fullerene chemistry

Fullerene chemistry has come a long way since 1990, when the first bulk production of C60 was reported. In the past decade, progress in supramolecular chemistry has opened some remarkable and previously unexpected opportunities regarding the selective (multiple) functionalization of fullerenes and their (self)assembly into larger structures and frameworks. The purpose of this review article is to provide a comprehensive overview of these recent developments. We describe how macrocycles and cages that bind strongly to C60 can be used to block undesired addition patterns and thus allow the selective preparation of single-isomer addition products. We also discuss how the emergence of highly shape-persistent macrocycles has opened opportunities for the study of photoactive fullerene dyads and triads as well as the preparation of mechanically interlocked compounds. The preparation of two- or three-dimensional fullerene materials is another research area that has seen remarkable progress over the past few years. Due to the rapidly decreasing price of C60 and C70, we believe that these achievements will translate into all fields where fullerenes have traditionally (third-generation solar cells) and more recently been applied (catalysis, spintronics).

Synthesis of spiro[indolenine]-methanofullerenes via Deoxofluor promoted deoxygenative cyclopropanation of 1,2-(3-indole)-fullerenols

Deoxofluor-promoted intramolecular cyclopropanation of 1,2-(3-indole)fullerenols has been developed as a straightforward and efficient protocol for the synthesis of various spiro[indolenine]-methanofullerenes. This approach exhibits low cost, operational simplicity, and convenient conditions, and thus has potential application value.

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.

Chiral Open-[60]Fullerene Ligands with Giant Dissymmetry Factors

The optical resolution of open-[60]fullerenes has been limited to only one example since 1998, while the recent advances revealed the excellence of fullerenes as revisited chiral functional materials. Different from conventional chiral induction on [60]fullerene by a multiple-functionalization, a random disruption of the spherical π-conjugation is avoidable for open-[60]fullerenes. Moreover, the macrocyclic orifices enable a metal coordination which endows modulated electronic structures on chiral chromophores. Herein, we showcase Li⁺-coordination behavior and optical resolution of three chiral open-[60]fullerene ligands, showing a giant dissymmetry factor up to 0.20 owing to a congenital topology of the spherical π-conjugation.

NHC-Catalyzed Three-Component Hydroalkylation Reactions of [60]Fullerene: An Umpolung Approach to Diverse Monoalkylated Hydrofullerenes

A novel N-heterocyclic carbene-catalyzed three-component umpolung hydroalkylation of [60]fullerene with 4-(chloromethyl)-benzaldehydes/α,β-unsaturated aldehydes and alcohols/thioalcohols has been developed for the flexible and efficient preparation of diverse monoalkylated hydrofullerenes. Organic catalysis, broad substrate scope, excellent functional group tolerance, and products with high diversity and complexity levels are attractive features of this protocol.

Palladium-catalyzed decarboxylative [2 + 3] cyclocarbonylation reactions of [60]fullerene: selective synthesis of [60]fullerene-fused 3-vinylcyclopentan-4-ones and cyclopentane-4-carbaldehydes

A new palladium-catalyzed decarboxylative strategy has been developed toward direct cyclocarbonylation of [60]fullerene, selectively furnishing novel [60]fullerene-fused 3-vinylcyclopentan-4-ones and cyclopentane-4-carbaldehydes.

Palladium-catalyzed three-component 1,4-aminoarylation of [60]fullerene with aryl iodides and N-methoxysulfonamides, and further transformations

The palladium-catalyzed three-component 1,4-aminoarylation of [60]fullerene afforded 1,4-(aryl)(sulfonamide)[60]fullerenes, of which the sulfonamide group could be replaced by a (hetero)aryl, malonate ester or allyl group in the presence of FeCl3.

Reductive Decarbonylation of a Cage-Opened C60 Derivative

The decarbonylation of a cage-opened C₆₀ derivative was examined by employing single-electron reductants. During the reaction, an H₂O molecule was spontaneously encapsulated inside the cage (up to 78%) through the thus-formed 14-membered-ring orifice even though the H₂O encapsulation had long been considered to require an orifice consisting of at least 16 atoms. The crystallographic analysis revealed an orifice shape closer to a circle which significantly contributes to the decreased activation barrier for the H₂O encapsulation.