Synthesis,structure, and properties of novel open-cage fullerenes having heteroatom(s) on the rim of the orifice

A thermal liquid-phase reaction of fullerene C(60) with 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine afforded aza-open-cage fullerene derivative 5 having an eight-membered-ring orifice on the fullerene cage. Compound 5 was found to undergo oxidative ring-enlargement reactions with singlet oxygen under photo-irradiation to give azadioxo-open-cage fullerene derivatives 9 and 10, which have a 12-membered-ring orifice, in addition to a small amount of azadioxa-open-cage fullerene derivative 11, which has a 10-membered-ring orifice. A thermal reaction of 9 with elemental sulfur in the presence of tetrakis(dimethylamino)ethylene resulted in further ring-enlargement to give azadioxothia-open-cage fullerene derivative 15, which has a 13-membered-ring orifice. The structures of 5 and 15 were determined by X-ray crystallography, while those of 9, 10, and 11 were confirmed by the agreement of observed (13)C NMR spectra with those obtained by DFT-GIAO calculations. These reactions were rationalized based on the results of molecular orbital calculations. Following electrochemical measurements, compounds 9 and 10, which have two carbonyl groups on the rim of the orifice, were found to be more readily reduced than C(60) itself (the first reduction potential was found to be 0.2 V lower than that of C(60)), while the first reduction potentials of other open-cage fullerene derivatives, 5, 11, and 15, were nearly the same as that of C(60).     

Synthesis of 18-membered open-cage fullerenes through controlled stepwise fullerene skeleton bond cleavage processes and substituent-mediated tuning of the redox potential of open-cage fullerenes

Oxidation of the fullerenediol C(60)(OH)(2)(O)(OAc)(OOtBu)(3) with PhI(OAc)(2) yields the open-cage fullerene derivative C(60)(O)(2)(O)(OAc)(OOtBu)(3)2 with an 11-membered orifice. Compound 2 reacts with aniline to form a new open-cage derivative with a 14-membered orifice, which yields an 18-membered open-cage fullerene derivative upon addition of another molecule of aniline. Two different types of aniline derivatives with either electron-donating or electron-withdrawing substituents can be added sequentially, affording an unsymmetrical moiety in the open-cage structure. Reduction potentials of the 18-membered open-cage fullerene derivatives can be fine-tuned by changing the substituents on the aniline. The results provide new insights about the mechanism of open-cage reactions of fullerene-mixed peroxide.     

Synthesis of [59]fullerenones through peroxide-mediated stepwise cleavage of fullerene skeleton bonds and X-ray structures of their water-encapsulated open-cage complexes

Fullerene skeleton modification has been investigated through selective cleavage of the fullerene carbon-carbon bonds under mild conditions. Several cage-opened fullerene derivatives including three [59]fullerenones with an 18-membered-ring orifice and one [59]fullerenone with a 19-membered-ring orifice have been prepared starting from the fullerene mixed peroxide 1, C60(OOtBu)6. The prepositioned tert-butyl peroxy groups in 1 serve as excellent oxygen sources for formation of hydroxyl and carbonyl groups. The cage-opening reactions were initiated by photoinduced homolysis of the tBu-O bond, followed by sequential ring expansion steps. A key step of the ring expansion reactions is the oxidation of adjacent fullerene hydroxyl and amino groups by diacetoxyliodobenzene (DIB). Aminolysis of a cage-opened fullerene derivative containing an anhydride moiety resulted in multiple bond cleavage in one step. A domino mechanism was proposed for this reaction. Decarboxylation led to elimination of one carbon atom from the C60 cage and formation of [59]fullerenones. The cage-opened [59]fullerenones were found to encapsulate water under mild conditions. All compounds were characterized by spectroscopic data. Single-crystal structures were also obtained for five skeleton-modified derivatives including two water-encapsulated fulleroids.     

A bowl-shaped fullerene encapsulates a water into the cage

The sequential carbon-carbon bond cleaving reactions of the diketone derivative of C60 with o-phenylenediamine give a novel bowl-shaped fullerene bearing a 20-membered ring orifice. The product reversibly encapsulates a water molecule into the fullerene cage for the first time.     

100% encapsulation of a hydrogen molecule into an open-cage fullerene derivative and gas-phase generation of H2@C60

By applying high-pressure H2 to a new fullerene derivative, C63NO2SPh2Py (1), having a 13-membered-ring orifice, 100% incorporation of a H2 molecule into the fullerene cage has been achieved for the first time. This result substantiates the theoretical calculations indicating that the energy barrier required for H2 insertion through an orifice in 1 is considerably lower than that for the previously reported derivative with the largest orifice among open-cage fullerenes synthesized thus far. Upon matrix-assisted laser desorption/ionization mass spectroscopy, the removal of organic addends from the fullerene derivative 1 encapsulating H2 and restoration of the pristine C60 cage, which retains approximately one-third of incorporated H2, have been observed.     

Open-cage fullerene derivatives with 15-membered-ring orifices

The addition reaction of the N-MEM-ketolactam derivative of [60]fullerene with phenyl, p-Br-phenyl, and p-MeO-phenyl hydrazines proceeds regioselectively, affording three open-cage fullerene derivatives bearing a 15-membered-ring orifice on the fullerene cage. Both experimental data and theoretical calculations were utilized for the structure determination of the new [60]fullerene adducts.     

The reaction of fullerene C(60) with phthalazine: the mechanochemical solid-state reaction yielding a new C(60) dimer versus the liquid-phase reaction affording an open-cage fullerene.

The reaction of fullerene C(60) with phthalazine was studied both in solution and in the solid state using the high-speed vibration-milling technique. The reaction in solution gave open-cage fullerene derivative 1 in 44% yield by a one-pot reaction. In contrast, the solid-state reaction afforded dimeric derivative 2 as the sole product. Dimeric derivative 2 was found to undergo intramolecular [2 + 2] cycloaddtion between the two C(60) cages located in close proximity to give a new C(60) dimer 6 in quantitative yield. The structures of these new derivatives of C(60) were determined by spectroscopic methods, and the electrochemical behavior of 2 and 6 was also studied.     

A novel migrative addition reaction of hydrazines to the diketone derivative of C60

A novel addition reaction of an aromatic hydrazine to the diketone derivative of C60 occurs highly regioselectively with an unusual migration of two hydrogen atoms from the hydrazine to the fullerene and affords a fluorescent product having a methylene carbon along the orifice.     

Open-cage fullerene derivatives having 11-, 12-, and 13-membered-ring orifices: chemical transformations of the organic addends on the rim of the orifice

A novel open-cage [60]fullerene derivative, having two sulfur atoms on the rim of its 13-membered-ring orifice, has been isolated and characterized. Extensive studies on the N-MEM group reactivity of this as well as other previously reported open-cage [60]fullerene derivatives led to several new open-cage [60]fullerene adducts.     

Open-cage fullerene derivatives suitable for the encapsulation of a hydrogen molecule

The encapsulation of molecular hydrogen into an open-cage fullerene having a 16-membered ring orifice has been investigated. It is achieved by the pressurization of H2 at 0.6-13.5 MPa to afford endohedral hydrogen complexes of open-cage fullerenes in up to 83% yield. The efficiency of encapsulation is dominantly dependent on both H2 pressure and temperature. Hydrogen molecules inside the C60 cage are observed in the range of -7.3 to -7.5 ppm in 1H NMR spectra, and the formations of hydrogen complexes are further confirmed by mass spectrometry. The trapped hydrogen is released by heating. The activation energy barriers for this process are determined to be 22-24 kcal/mol. The DSC measurement of the endohedral H2 complex reveals that the escape of H2 from the C60 cage corresponds to an exothermic process, indicating that encapsulated H2 destabilizes the fullerene.     

Rearrangement of the cyclohexadiene derivatives of C60 to bis(fulleroid) and bis(methano)fullerene: structure,stability, and mechanism

The cyclohexadiene derivative of C(60) rearranges photochemically to bis(fulleroid) (two [6,5] open structure) and bis(methano)fullerene (two [6,6] closed structure). During this process, a [6,5] open/[6,6] closed intermediate is observed. The isolated intermediate undergoes photochemical rearrangement to bis(fulleroid) and bis(methano)fullerene. On the other side, it undergoes retrorearrangement to the starting material in the dark. The structure and energetics of these C(60) derivatives have been studied at the AM1, PM3, RHF, and B3LYP levels of theory. It is found that bis(fulleroid) bearing four tert-butoxycarbonyl substituents is 5.8 kcal/mol (B3LYP) more stable than the corresponding bis(methano)fullerene. The isolated intermediate having the [6,5] open/[6,6] closed structure is 6.7 kcal/mol more favorable than the previously proposed two [6,5] closed intermediate, and the formation of this compound is well explained by the di-pi-methane rearrangement. (13)C NMR calculation at the B3LYP level reproduced the experimental chemical shifts with very good accuracy for each molecular system. Theoretical studies mainly at the unrestricted B3LYP level on singlet and triplet state potential energy surfaces on fullerene derivatives support the di-pi-methane rearrangement mechanism. The previously proposed symmetrical [4+4]/[2+2+2] and the novel proposed unsymmetrical di-pi-methane pathways may coexist during the reaction.     

Face-to-face C6F5-[60]fullerene interaction for ordering fullerene molecules and application to thin-film organic photovoltaics

Treatment of [60]fullerene with potassium methylnaphthalenide and excess C(6)F(5)CH(2)Br afforded 1,4-bis(pentafluorobenzyl)[60]fullerene, the study of which showed that there is a face-to-face interaction between [60]fullerene and a perfluoro aromatic ring, allowing the molecule to be utilized for high-performance organic photovoltaic devices.     

Efficient synthesis of open-cage fullerene derivatives having 16-membered-ring orifices

The synthesis of 10 new open-cage fullerene derivatives with a 16-membered-ring orifice is being reported. These compounds, derived from the regioselective addition reaction of an aromatic hydrazine or hydrazone to isomeric diketone derivatives of C(60), were isolated in moderate to excellent yields.     

Production of monoclonal antibodies against fullerene C60 and development of a fullerene enzyme immunoassay

The aim of the present study was to produce monoclonal anti-fullerene C(60) antibodies and to develop the enzyme immunoassay for the detection in the first use of free fullerene C(60) both in solutions and in multicomponent biological probes. The immunization of mice with the conjugate of fullerene C(60) carboxylic derivative with thyroglobulin synthesized by carbodiimide activation led to the production of eight clones of anti-fullerene antibodies. The specificity of the antibody-fullerene binding was confirmed. Indirect competitive enzyme-linked immunosorbent assay (ELISA) was developed for the determination of water-soluble protein-conjugated fullerene, the fullerene aminocaproic acid, fullerenol and for pristine fullerene in solution. To solubilize extremely hydrophobic free fullerene C(60) a specially selected water-organic mixture compatible with immunoassay was proposed. The detection limit of free fullerene C(60) in solution was 2 μg L(-1). Fullerene C(60) was also detected by ELISA in organ homogenates of rats intraperitoneally or intragastrically administered with fullerene. To reduce the influence of biomatrices on the assay results a technique was developed for the biological sample pretreatment by the extraction of C(60) from bioprobe by toluene followed by the evaporation of toluene and dissolution of the fullerene-containing extract in the selected water-organic media. The ELISA procedure in the first use allowed the detection of fullerene C(60) in different tissues.     

Synthesis and properties of endohedral C60 encapsulating molecular hydrogen

We report the details of our study to synthesize a new endohedral fullerene, H2@C60, in more than 100 mg quantities by closure of the 13-membered ring orifice of an open-cage fullerene using four-step organic reactions. The 13-membered ring orifice in a previously synthesized open-cage fullerene incorporating hydrogen in 100% yield was reduced to a 12-membered ring by extrusion of a sulfur atom at the rim of the orifice, and the ring was further reduced into an eight-membered ring by reductive coupling of two carbonyl groups also at the orifice. Final closure of the orifice was completed by a thermal reaction. Purification of H2@C60 was accomplished by recycle HPLC. A gradual downfield shift of the NMR signal for the encapsulated hydrogen observed upon reduction of the orifice size was interpreted based on the gauge-independent atomic orbital (GIAO) and the nucleus-independent chemical shift (NICS) calculations. The spectral as well as electrochemical examination of the properties of H2@C60 has shown that the electronic interaction between the encapsulated hydrogen and outer C60 pi-system is quite small but becomes appreciable when the outer pi-system acquires more than three extra electrons. Four kinds of exohedral derivatives of H2@C60 were synthesized. The tendency in the shift of the NMR signal of the inner hydrogen was found to be quite similar to that observed for the 3He NMR signal of the corresponding derivatives of 3He@C60.     

Trends in chemical shift dispersion in fullerene derivatives. Local strain affects the magnetic environment of distant fullerene carbons

13C NMR chemical shift assignments for 1,2-C60H2 (1) and a series of 13C-labeled fullerene derivatives with three-, four-, and five-membered annulated rings (2-4) were assigned using 2D INADEQUATE spectroscopy and examined for trends that correspond to the changes in strain in the fullerene cage. Chemical shifts of equivalent carbons from 1-4 show that eight carbons trend downfield (carbons 5, 7, 8, 9, 11, 15, 16, 17) and the remaining six carbons (4, 6, 10, 12, 13, 14) trend upfield with increasing ring size. While the average chemical shift is nearly constant, the dispersion is greatest when the local strain is the least, in 1,2-C60H2 (1). 13C chemical shifts are not well correlated with trends in ring size, with strain as measured by the pyramidalization angle of nearby carbons, or with the geometry of the fullerene cage. We interpret the results as evidence that subtle geometrical changes lead to modulation of the strength of ring currents near the site of addition and, in turn, the magnetic field generated by these ring currents affects the chemical shift of carbons on the far side of the fullerene core. These results highlight ring currents as being critically important to the determination of 13C chemical shifts in fullerene derivatives.     

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.     

Photophysical properties of a 1,2,3,4,5,6-hexasubstituted fullerene derivative

The photophysical properties of a novel 1,2,3,4,5,6-hexasubstituted fullerene derivative (1) are examined in this study. In addition to the ground state absorption spectrum of 1, we report its triplet-triplet absorption spectrum and molar extinction coefficient (Deltae(T-T)), as well as the triplet quantum yield (PhiT), lifetime (tauT), and energy (ET). The saturation of a single six-member ring on the fullerene cage results in significant changes in the triplet state properties as compared to that of pristine C60. The triplet-triplet absorption spectrum shows a hypsochromic shift in long wavelength absorption, and both the triplet state lifetime and the triplet quantum yield are decreased. The triplet energy was found to be similar to that of C60. In addition, the quantum yield (PHI(delta)) of singlet oxygen generated by 1 was calculated and is found to be significantly less than in the case of C60.     

Novel cycloaddition reaction of [60]fullerene with carbonyl ylides generated from epoxides

The thermal reaction of [60]fullerene (C60) with the carbonyl ylides generated in situ from trans-epoxides to give C60-fused tetrahydrofuran derivatives has been investigated. The reaction of C60 with trans-2-benzoyl-3-aryloxiranes afforded only cis-products, while the reaction of C60 with 2-cyano-2-ethoxycarbonyl-3-aryloxiranes gave exclusively or predominantly cis isomers. The isomeric distributions of the latter reactions were drastically affected by the substituent on the phenyl ring.     

Single crystal X-ray structure of tetrahedral C60F36: the most aromatic and distorted fullerene

Tetrahedral C60F36 is shown by its single-crystal X-ray structure to be the most aromatic (and distorted) fullerene derivative, having four planar hexagons with almost equal bond lengths, the average of which (1.373 A) is the same as in C60F18; one exceptionally long FC-CF bond (1.665 A) corresponds to the similarly long bond in C60F18 (a motif of T C60F36) and is likely to be the site of oxygen insertion in C60F36O.