Open-cage Fullerene Derivatives Research Articles

Synthesis of η2-platinum complexes on the rim of open-cage fullerenes

Three new open-cage fullerene derivatives with a 19-membered orifice have been prepared, two of which readily formed Pt complexes when treated with Pt(PPh3)4. Several related open-cage fullerene derivatives were also found to form very stable platinum complexes, which could be purified by chromatography on silica gel under ambient conditions. Single crystal X-ray diffraction data revealed that the Pt metal formed η2-type coordination pattern with a fullerene double bond on the rim of the orifice. Regio-selectivity of the platinum coordination is determined by the electron density of double bonds on the cage. The most electron deficient double bond shows the highest reactivity.

Open-Cage Fullerene as Molecular Container for F- , Cl- , Br- and I.

A 19-membered open-cage fullerene derivative was prepared from C60 in 7 steps and 5.5 % yield through the peroxide-mediate pathway. There are four carbonyl groups, an ether oxygen and a quinoxaline moiety on the rim of the orifice. A chloride anion could be inserted into its cavity by heating with hydrochloric acid at 60 °C for 4 h. Encapsulation of fluoride, bromide and iodide anions was also achieved at slightly more forcing conditions, 90 °C for 14 h. Single crystal X-ray structures of the sodium salt of the chloride and the bromide encapsulated derivatives were obtained, which showed the halide anion in the center of the cavity and two sodium cations connecting two cages through coordination to the oxygen atoms on the rim of the orifices. The halide encapsulation ratio is quantitative in the isolated products.

Preparation of π-extended fullerene derivatives through addition of phenylenediamine to open-cage fullerene derivatives

Open-cage fullerenes with a quinoxaline moiety on the rim of the orifice showed evident π-system extension effect on the NMR and UV-Vis spectra.

An H2 O2 Molecule Stabilized inside Open-Cage C60 Derivatives by a Hydroxy Stopper.

An H2 O2 molecule was isolated inside hydroxylated open-cage fullerene derivatives by mixing an H2 O2 solution with a precursor molecule followed by reduction of one of carbonyl groups on its orifice. Depending on the reduction site, two structural isomers for H2 O2 @open-fullerenes were obtained. A high encapsulation ratio of 81 % was attained at low temperature. The structures of the peroxosolvate complexes thus obtained were studied by 1 H NMR spectroscopy, X-ray analysis, and DFT calculations, showing strong hydrogen bonding between the encapsulated H2 O2 and the hydroxy group located at the center of the orifice. This OH group was found to act as a kinetic stopper, and the formation of the hydrogen bonding caused thermodynamic stabilization of the H2 O2 molecule, both of which prevent its escape from the cage. One of the peroxosolvates was isolated by HPLC, affording H2 O2 @open-fullerene with 100 % encapsulation ratio, likely due to the intramolecular hydrogen-bonding interaction.

Dynamics and magnetic properties of NO molecules encapsulated in open-cage fullerene derivatives evidenced by low temperature heat capacity

Low-temperature heat capacity analyses for an NO-encapsulated fullerene derivative revealed (i) low-energy motion and (ii) strong magnetic anisotropy of the NO molecule due to its orbital angular momentum. The low-energy motion was attributed to reorientational motions of the NO molecules, in which only a small number (n ∼ 0.04) of NO molecules were found to participate. The NO molecules were confirmed to be paramagnetic even at 1 K. Ab-initio calculation indicated that the magnetic properties of the NO unit strongly depended on its surroundings, allowing the conformation of the fullerene cage to be estimated.

(Invited) Synthesis and Properties of Endohedral Open-Cage Fullerenes

Open-cage fullerene derivatives are fascinating molecules because a small molecule can be introduced inside the fullerene cage through the opening. When the NMR active molecules are introduced inside the open-cage fullerene derivatives, the resulting endohedral species are used for the study with the encapsulated molecule as a magnetic probe. First, the regioselectivity in the Diels.Alder reaction of an unsymmetrical open-cage C60 derivative with anthracene was studied. By using an encapsulated H2 molecule as a magnetic probe, the product population was successfully evaluated in detail, indicating the formation of approximately ten compounds as major components. The NICS calculations showed a close resemblance to the observed 1H NMR spectrum, which allowed for a facile characterization of the products. Theoretical studies on the formation of all 29 possible anthracene adducts were also performed. The results indicated that the regioselectivity is strongly governed by steric factors, values of the frontier orbital coefficients, and thermodynamic stabilities. Single-crystal X-ray analysis of the dominant compound revealed the supramolecular architecture between the anthracene moiety and the Π-sphere of a neighboring molecule.[1] Second, The H2O/CH2=CH2-type hydrogen-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, we performed 1H NMR spectroscopic studies that demonstrated the monotonic downfield shift of the proton signal corresponding to H2O with remarkable rotational perturbation by lowering the temperature. From the temperature dependence of the angular momentum correlation time, the interaction energy was quantitatively estimated to be ca. 0.3 kcal/mol. The computational studies were thoroughly conducted to clarify its inherent nature. As a consequence, the orientation of H2O was found to play a prominent role in varying the bonding strength as well as contribution from the electrostatic attraction and orbital-orbital interaction significantly driven by the favorable orbital overlap.[2][1] Probing the Regioselectivity by Encapsulated H2: Diels-Alder Reaction of a Cage-Opened C60 Derivative with Anthracene, Hashikawa, Y.; Murata, Y. Chem. Eur. J. 2019, 25, 2482-2485.[2] H2O/Olefinic-Π Interaction inside a Carbon Nanocage, Hashikawa, Y.; Murata, Y. J. Am. Chem. Soc. 2019, 141, 12928-12938.

(Invited) Preparation of Open-Cage Fullerene Derivatives By Rhodium(I)-Catalyzed [2+2+2] Cycloaddition of Diynes and C60: Synthesis, Computational Studies and Application in Perovskite Solar Cells

Since the discovery of C60 in 1985 [1], fullerenes have attracted the attention of chemists due to their unique structure, properties and reactivity, along with their potential applications in a variety of fields ranging from materials science to biomedicine [2–3]. The preparation of cyclohexadiene-fused C60 derivatives can be achieved by [2+2+2] cycloaddition reactions of C60 with alkynes [4–6]. This particular class of fullerene derivatives is interesting from the synthetic point of view because they can be converted into the corresponding open-cage bis(fulleroids) when subjected to photochemical conditions [7]. Based on our previous theoretical DFT study that showed the viability of a rhodium-catalyzed [2+2+2] cycloaddition reaction of two alkynes and C60 [8], here we report the first example of [2+2+2] cycloaddition involving C60 and diynes under catalytic conditions promoted by a rhodium(I) catalyst, which leads to the formation of a series of bis(fulleroids) [9]. The process takes place in a single step and no photoexcitation is required. The process mechanism has been studied by means of DFT calculations, proving that the cyclohexadiene-fused intermediate resulting from a [2+2+2] cycloaddition evolves into the final product through a Rh-catalyzed di-π-methane rearrangement. Finally, the electrochemical behavior of the synthesized products has also been studied, as well as their performance as electron transporting materials (ETMs) in perovskite solar cells (PSCs) [10].

Concise Synthesis of Open-Cage Fullerenes for Oxygen Delivery.

Open-cage fullerenes with a 19-membered orifice were prepared in three steps from C60 . The key step for cage-opening is aniline mediated ring expansion of a fullerene-mixed peroxide with a ketolactone moiety on the orifice. Release of ring strain on the spherical fullerene cage served as the main driving force for the efficient cage-opening sequence. Encapsulation of oxygen could be achieved at room temperature under moderate pressure (50 atm) and the encapsulated oxygen could be released slowly under ambient conditions. The activation energy of the oxygen-releasing process is 18.8 kcal mol-1 and the half-life at 37 °C was 73 min, which makes this open-cage fullerene derivative a potential oxygen-delivery material.

C60-Fused Ketoamides Formation in Self-Sensitized Photo-Oxidation of 2-Fulleropyrrolines and Its Dynamic Study

Given the immense and potential applications in materials science and biological science, fullerenes and their derivatives have attracted extensive attention.1 A large number of chemical reactions have been developed to functionalize the fullerenes.2 In the past two decades, transition-metal-catalyzed C-H activation reaction has become one of the important strategies in the preparation of multifunctional and composite material.3 Most of its reactions use directing groups to form C60-fused heterocycles or C60-fused carbocycles, such as fulleropyrrolines,4 fullerotetrahydropyridazines,5 fulleroindolines,6 C60-fused dihydrofuran7 and C60-fused dihydrophenanthrenes8 and so on. Fulleropyrrolines are a kind of important fullerene derivative, which may have promising applications in designing and synthesizing novel organic photovoltaic materials due to the heterocyclic ring bearing a C=C bond, which can be utilized to construct a series of completely conjugated donor-acceptor (D-A) systems. Thus, it is still a demand to develop more practical approach to prepare fulleropyrrolines.9 We have recently investigated the palladium-catalyzed N-heteroannulation reaction of C60 with benzoyl hydrazone esters and unexpectedly synthesized N-unsubstituted 2-fulleropyrrolines. Notably, investigation of these reactions resulted in our discovery of the photo-oxidation of 2-fulleropyrrolines through enamine C=C bond cleavage to yield the corresponding dicarbonyl fullerene derivatives. Foot et al first reported the self-sensitized photooxidation of the C60-fused cycloadducts.10 Komatsu et al described the photochemical reaction of the open-cage fullerene derivative with singlet oxygen.11 Kabe et al also developed the synthesis of ring orifice in open-cage fullerenes by photooxygenation of azafulleroid.12 Nevertheless, the photo-oxidation of 2-fulleropyrrolines have never been explored. Herein, the self-sensitized photo-oxidation of 2-fulleropyrrolines was first discovered under very mild condition to yield a ketoamides fullerene derivative in high yields. The reaction kinetics of this self-sensitized photo-oxidation has been explored, which indicating that this photo-oxidation process is a first-order reaction and possessing low reaction activation energy (2.79 KJ/mol). Moreover, a possible mechanism related to the observed products was proposed Reference: For general reviews, see: (a) Guldi, D. M.; Illescas, B. M.; Atienza, C. M. Chem. Soc. Rev. 2009, 38, 1587. (b) Perez, E. M.; Martín, N. Chem. Soc. Rev. 2008, 37, 1512. (c) Thilgen, C.; Diederich, F. Chem. Rev, 2006, 106, 5049. (d) Nakamura, E.; Isobe, H. Acc. Chem. Res, 2003, 36, 807. (e) Diederich, F.; Gómez-López, M. Chem. Soc. Rev, 1999, 28, 263.Hirsch, A.; Brettreich, M. John Wiley & Sons, 2006.(a) Neufeldt, S. R.; Sanford, M. S. Org. Lett, 2009, 12, 532. (b) Stowers, K. J.; Sanford, M. S. Org. Lett, 2009, 11, 4584. (c) Deprez, N. R.; Sanford, M. S. J. Am. Chem. Soc, 2009, 131, 11234. (d) Desai, L. V.; Stowers, K. J.; Sanford, M. S. J. Am. Chem. Soc, 2008, 130, 13285.Wu J.; Liu, C.-X.; Wang, H.-J.; Li, F.-B.; Shi, J.-L.; Liu, L.; Li, J.-X.; Liu, C.-X.; Huang, Y.-S. J. Org. Chem, 2016, 81, 9296.Jiang, S.-P.; Liu, Z.; Lu, W.-Q.; Wang, G.-W. Org Chem Front. 2018, 5, 1188.Zhu, B.; Wang, G.-W. J. Org. Chem, 2009, 74, 4426.Yan, Y.-T.; Gao, W.; Jin, B.; Peng, R.-F.; Chu, S.-J. J. Org. Chem . 2018, 83, 672.Zhou, D.-B.; Wang, G.-W. Org. Lett. 2015, 17, 1260Vail, S. A.; Krawczuk, P. J.; Guldi, D. M.; Palkar, A.; Echegoyen, L.; Tomé, J. P. C.; Fazio, M. A.; Schuster, D. I. Chem. - Eur. J. 2005, 11, 3375. 10 (a) Zhang, X.-J.; Romero, A.; Foote, C. S. J. Am. Chem. Soc. 1993, 115, 11024. (b) Zhang, X.-J.; Foote, C. S. J. Am. Chem. Soc. 1995, 117, 4271. (a) Murata, Y.; Komatsu, K. Chem Lett . 2001, 30, 896. (b) Murata Y, Murata M. J. Org. Chem . 2001, 66, 8187(a) Hachiya, H.; Kabe, Y. Chem L ett . 2009, 38, 372. (b) Tanaka, T.; Nojiri, R.; Sugiyama,Y.; Sawai,.R. Org. Biomol. Chem. 2017, 15, 6136. Figure 1

Wavelength-Dependent Efficiency of Sequential Photooxygenation: C=C Bond Cleavage on Open-Cage C60 Derivatives.

We have studied the efficiency of the C=C double bond cleavage on open-cage fullerene C60 derivatives by singlet oxygen using four different LED lamps including UV, blue, green, and red radiation. The results indicate that red radiation is the most efficient for this photochemical oxidation owing to the sufficient penetration of the longer-wavelength light. By applying this method to a 2-methoxyethoxymethyl-substituted azafulleroid derivative, we demonstrated the sequential double photooxygenation which provides a symmetric diketo imide derivative having a 15-membered-ring opening via stepwise cleavage of two C=C double bonds. Using a H2 -encapsulating derivative, we further examined the size of the opening by comparison with the structural isomer, based on H2 -release experiments and theoretical calculations.

Construction of a Metal-Free Electron Spin System by Encapsulation of an NO Molecule Inside an Open-Cage Fullerene C60 Derivative.

A reactive radical species, nitric oxide (NO), was encapsulated in a unimolecular form inside an open-cage fullerene derivative under high-pressure conditions in the solid state. Surprisingly, the molecular complex showed sharp 1 H NMR signals despite the existence of the paramagnetic species inside the carbon cage. Owing to the paramagnetic shifts, the escape rate of the NO was determined experimentally. After constructing a stopper on the rim of the opening, the NO was found to stay inside the cage even at 50 °C. The ESR measurements of the powdery sample showed paramagnetic properties at low temperature. The single-crystal X-ray structure analysis clearly demonstrated the existence of the encapsulated NO molecule, suggesting rapid rotation inside the cage. The 1 H NMR chemical shifts displayed a large temperature dependence owing to the paramagnetic effects.

Expeditious Preparation of Open-Cage Fullerenes by Rhodium(I)-Catalyzed [2+2+2] Cycloaddition of Diynes and C60 : An Experimental and Theoretical Study.

A novel methodology to transform C60 into a variety of open-cage fullerene derivatives by employing rhodium(I) catalysis has been developed. This transformation encompasses a partially intermolecular [2+2+2] cycloaddition reaction between diynes 1 and C60 to deliver a cyclohexadiene-fused fullerene, which concomitantly undergoes a formal [4+4]/retro-[2+2+2] rearrangement to deliver open-cage fullerenes 2. Most notably, this process occurs without the need of photoexcitation. The complete mechanism of this transformation has been rationalized by DFT calculations, which indicate that, after [2+2+2] cycloaddition, the cyclohexadiene-fused intermediate evolves into the final product through a Rh-catalyzed di-π-methane rearrangement followed by a retro-[2+2+2] cycloaddition. The obtained open-cage fullerenes can be derivatized by Suzuki-Miyaura cross-coupling or subjected to ring expansion to deliver a 12-membered ring orifice in the fullerene structure. Overall, the methodology presented constitutes a straightforward entry to functional open-cage C60 fullerene derivatives by employing catalytic methods.

(Invited) Synthesis and Properties of Open-Cage Fullerene Derivatives

Endohedral fullerenes represent caged-clusters of carbon encapsulating metal ions, metal clusters, atoms, and molecules. Although their syntheses mainly rely on physical methods under harsh conditions, organic synthesis has been attracting interests to realize molecule-encapsulating fullerenes owing to high selectivity of fullerene cages and high yields of desired products. The "molecular surgery" was able to be applied to fullerene C70 in spite of difficulties in characterization of products due to the low symmetry compared with C60. Importantly, reflecting the larger inner space than C60, two small molecules were introduced inside open-cage C70 derivatives to afford the corresponding doubly-encapsulating C70 such as (H2O)2@C70[1] and (H2O-HF)@C70[2] in addition to mono-encapsulating H2O@C70 and HF@C70. On the other hand, applying combination of the molecular surgery and ion implantation, doubly-encapsulating (H2-N)@C70 was able to be generated, in which the atomic nitrogen interacts with the hydrogen molecule, without forming covalent bonds.[3]

Synthesis and Structure of an Open-cage C69O Derivative

A novel open-cage fullerene derivative having a C69O framework was synthesized, demonstrating that the reactivity of an open-cage C70 with a tetraketone moiety was quite different compared with its C60 analogue. The structure of the open-cage C69O was unambiguously determined by single-crystal X-ray diffraction analysis and its electrochemical properties were compared with its sulfur analogue.

Structural modification of open-cage fullerene C60 derivatives having a small molecule inside their cavities

We studied the chemical modifications of open-cage fullerene C60 derivatives encapsulating a small molecule such as H2 and H2O. In these reactions, the entrapped molecules can be used as a probe for monitoring the reactions. The solubilizing group (methoxyethyl group) was successfully introduced on the bis(hemiketal) moiety in the open-cage C60 derivative. Further specific reactions were also investigated for 2-methoxyethoxymethyl (MEM)-substituted C60 derivatives.

Synthesis of C58 Open-Cage Fullerene Derivatives

Several analogous C₅₈ open-cage fullerene derivatives have been prepared through silver acetate mediated decarboxylation of the corresponding C₅₉ open-cage precursors. These C₅₈ open-cage fullerene derivatives can trap one water molecule under mild conditions as shown by spectroscopic data and single-crystal X-ray analysis.

ChemInform Abstract: Peroxide‐Mediated Selective Cleavage of [60]Fullerene Skeleton Bonds: Towards the Synthesis of Open‐Cage Fulleroid C55O5

AbstractReview: [49 refs.

ChemInform Abstract: Synthesis, Properties and Transformations of Fullerene Peroxides

AbstractReview: 143 refs.

Open-cage fullerene with a stopper acts as a molecular vial for a single water molecule

An open-cage fullerene derivative with three carbonyl groups on the rim of the orifice reacts with o-diaminobenzene reversibly to form a tetrahydrofuran moiety above the orifice.

Peroxide-mediated selective cleavage of [60]fullerene skeleton bonds: towards the synthesis of open-cage fulleroid C55O5.

Replacement of a pentagon in [60]fullerene with five oxygen atoms yields the open-cage compound C55O5 with five carbonyl groups on the rim of the orifice. Our attempts to synthesize such a target molecule starting from C60 have led us to prepare the fullerene-mixed peroxides such as C60(OO-t-Bu)6 with all the peroxo addends surrounding the same pentagon. Further investigations of the peroxide chemistry have generated various open-cage fullerene derivatives, including the carbon monoxide encapsulated endohedral compound CO@C59O6. This Personal Account mainly discusses peroxide-based processes resulting in selective cleavage of the fullerene skeleton bonds.