Yoshifumi Hashikawa

The macroscopic-scale syntheses of the first endohedral aza[60]fullerenes X@C59N (X = H2O, H2) were achieved in two different ways: (1) synthesis from endohedral fullerene H2O@C60 as a starting material and (2) molecular surgical synthesis from a C59N precursor having a considerably small opening. In the neutral state of H2O@C59N, we expected the H-bonding interaction or repulsive N-O interaction between entrapped H2O and a nitrogen atom on the C59N cage. However, an attractive electrostatic N-O

The palladium-catalyzed cyclization on the fullerene C₆₀ cage has been achieved using several aryl halides and C₆₀. This reaction was found to be accelerated by the addition of pivalic acid, which can be rationally explained by the computational study based on the concerted metalation-deprotonation mechanism. We also demonstrated the regioselective π-functionalization using prefunctionalized designed molecules possessing the same substructure on the C₆₀ cage. The

Abstract A water molecule fixed within [60]fullerene is the simplest form of water available in meatspace. It was first artificially made by us in 2011. Since then, anomalies of water molecules free from any hydrogen-bonding have been discovered in succession. In this account, we summarize the research progress in the past decade from the aspect of synthesis, derivatization, and reactivity of fullerenes with water inside as well as their quantum and classical dynamics.

We have synthesized an open-cage C60 derivative having three hydroxy groups arranged in close proximity on the opening, which realized a single but hydrogen-bonded water molecule inside its cavity. The confined H2O molecule showed characteristic translational and rotational motions via the formation/cleavage of H-bonds. It is worth noting that the confined H2O molecule is less acidic and less basic than bulk water.

A novel open-cage fullerene C60 derivative having a bis(hemiketal) moiety was synthesized by the reaction of C60-N-MEM-ketolactam (MEM: 2-methoxyethoxymethyl) with N-methylmorpholine N-oxide in the presence of water. The structure was clearly determined by single crystal X-ray analysis. Further enlargement of the opening was performed by treatment with trifluoroacetic anhydride to give the tetraketo derivative having a 15-membered ring opening. For H2-insertion into the cage, the derivative was

The facile preparation of azafullerenyl cation C₅₉N⁺ has been achieved by the assistance of trifluoromethanesulfonic acid. The thus formed C₅₉N⁺ was quite stable in solution over 1 month and can be used as an intermediate for the electrophilic reaction. Applying this method to endohedral azafullerenes, corresponding cations (H₂@C₅₉N⁺ and H₂O@C₅₉N⁺) were prepared and the dynamic behavior

The H₂O/CH₂═CH₂-type hydrogen-bonding (H-bonding) model was experimentally constructed using a water complex of an open-cage C₆₀ derivative, in which an olefinic double bond and a single molecule of H₂O are geometrically confined. To investigate OH/π-type H-bonding, that is, H₂O···(C═C) interaction, we performed ¹H NMR spectroscopic studies that demonstrated the monotonic downfield shift of the proton signal correspondi

Novel open-cage fullerene C₆₀ derivatives with extended π-conjugation bearing thiophene rings exhibit long wavelength absorption due to characteristic intramolecular charge transfer transitions.

The concept of the bond polarization is a useful tool to understand chemical reactions and fundamental properties of compounds. However, experimental considerations are limited owing to its difficulty of reliable description. We demonstrated that geometrically isolated H₂ O inside the cage of fullerene C₆₀ is a possible probe to evaluate the polarization degree of covalent bonds C(C₆₀ )-X (X=heteroatom) on the C₆₀ cage. The ¹ H NMR relaxatio

Organophosphorus zwitterions are one of the most important but elusive intermediates for carbon-carbon bond formation in synthetic chemistry and biology. However, a lack of isolated examples due to their lability has hampered in-depth understanding of structures and their reaction mechanisms. In this study, we crystallographically reveal the solid-state structure of a phosha-Michael adduct engaged in a cage-opened C₆₀ skeleton, which is formed as a kinetic product. This compound exhib

Coalescence of [60]fullerenes potentially produces hypothetical nanocarbon assemblies with non-naturally occurring topologies. Since the discovery of [60]fullerene in 1985, coalesced [60]fullerene oligomers have only been observed as transient species by transmission electron microscopy during an oligomerization process under a high electron acceleration voltage. Herein, we showcase the rational synthesis of covalent assemblies consisting of inherently chiral open-[60]fullerenes. The crystallogr

The mature synthetic methodologies enable us to rationally design and produce chiral nanographenes (NGs), most of which consist of multiple helical motifs. However, inherent chirality originating from twisted geometry has just emerged to be employed in chiral NGs. Herein, we report a red-emissive chiral NG constituted of orthogonally arranged two-fold twisted π-skeletons at a contorted pyrene core which contributes to optical transitions of S₀→S₁ and vice versa. The thus-ob

Heterocyclic orifices in cage-opened fullerene derivatives are regarded as potential ligands toward metals or ions, being reminiscent of truncated fullerenes as a hypothetical class of macrocycles with spherical π-conjugation. Among a number of cage-opened examples reported thus far, the coordination ability and dynamic behavior in solution still remained unclear due to difficulties in structural determination with multiple coordination sites on the macrocycles. Herein, we present the detailed s

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 chir

Though [60]fullerene is an achiral molecular nanocarbon with I_h symmetry, it could attain an inherent chirality depending upon a functionalization pattern. The conventional chiral induction of C₆₀ relies mainly upon a multiple addition affording a mixture of achiral and chiral isomers while their chiral function would be largely offset by the existence of pseudo-mirror plane(s). These are major obstacles to proceed further study on fullerene chirality and yet leave its unde