首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 437 毫秒
1.
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 1H 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 1H NMR chemical shifts displayed a large temperature dependence owing to the paramagnetic effects.  相似文献   

2.
An open‐cage C60 tetraketone with a large opening was able to encapsulate N2 and CO2 molecules after its exposure to high pressures of N2 and CO2 gas. A subsequent selective reduction of one of the four carbonyl groups on the rim of the opening induced a contraction of the opening (→ 2 ) and trapped the guest molecules inside 2 . The thus‐obtained host–guest complexes N2@ 2 and CO2@ 2 could be isolated by recycling HPLC, and were found to be stable at room temperature. The molecular structures of N2@ 2 and CO2@ 2 were determined by single‐crystal X‐ray diffraction analyses, and revealed a short N?N triple bond for the encapsulated N2, as well as an unsymmetric molecular structure for the encapsulated molecule of CO2. The IR spectrum of CO2@ 2 suggested that the rotation of the encapsulated molecule of CO2 is partially restricted, which was supported by DFT calculations.  相似文献   

3.
Reaction of C63NO2(Ph)2(Py) ( 1 ) with o‐phenylenediamine and pyridine produces a mixture of C63H4NO2(Ph)2(Py)(N2C6H4) ( 2 ) and H2O@ 2 . Compound 2 is a new open‐cage fullerene containing a 20‐membered heterocyclic orifice, which has been fully characterized by NMR spectroscopy, high‐resolution mass spectrometry, and X‐ray crystallography. The elliptical orifice of 2 spans 7.45 Å along the major axis and 5.62 Å along the minor axis, which is large enough to trap water and small organic molecules. Thus, heating a mixture of 2 and H2O@ 2 with hydrogen cyanide and formaldehyde in chlorobenzene affords HCN@ 2 and H2CO@ 2 , respectively. The 1H NMR spectroscopy reveals substantial upfield shifts for the endohedral species (δ=?1.30 to ?11.30 ppm), owing to the strong shielding effect of the fullerene cage.  相似文献   

4.
Diels‐Alder cycloaddition reaction is useful for generation of covalent derivatives of fullerenes. Diels‐Alder reactions of C70 and dienes usually take place at the carbon‐carbon bond that has a short bond length in C70, while the bonds with long lengths are generally unreactive. In this paper, we investigated the reactivities of Li+@C70 and Li@C70 toward Diels‐Alder reactions with cyclohexadiene by means of density functional theory calculations. We found that the thermodynamic and kinetic reactivities of the fullerene cage are changed significantly after the encapsulation of the lithium ion or atom. The encapsulated lithium ion causes a remarkable decrease of the activation barrier for the cycloaddition reaction, which can be ascribed to the enhanced orbital interaction between cyclohexadiene and the fullerene cage. The unreactive bond with a long length in C70 is activated efficiently after the encapsulation of the lithium atom. According to the activation‐strain model analysis, the improved reactivity of the long bond is associated with the small deformation energy and large interaction energy of the reactants. Unlike conventional Diels‐Alder reactions that proceed through concerted mechanism, the reaction of Li@C70 and cyclohexadiene undergoes an unusual stepwise mechanism because of the open‐shell electronic structure of Li@C70.  相似文献   

5.
The thermal reaction of the endohedral metallofullerene La2@D2(10611)‐C72, which contains two pentalene units at opposite ends of the cage, with 5,6‐diphenyl‐3‐(2‐pyridyl)‐1,2,4‐triazine proceeded selectively to afford only two bisfulleroid isomers. The molecular structure of one isomer was determined using single‐crystal X‐ray crystallography. The results suggest that the [4+2] cycloaddition was initiated in a highly regioselective manner at the C? C bond connecting two pentagon rings of C72. Subsequent intramolecular electrocyclization followed by cycloreversion resulted in the formation of an open‐cage derivative having three seven‐membered ring orifices on the cage and a significantly elongated cage geometry. The reduction potentials of the open‐cage derivatives were similar to those of La2@D2‐C72 whereas the oxidation potentials were shifted more negative than those of La2@D2‐C72. These results point out that further oxidation could occur easily in the derivatives.  相似文献   

6.
A supramolecular/synthetic method has been devised to affix a sterically hindered substituent onto a fullerene guest encapsulated in a tubular host. A two‐wheeled complex of (C59N)‐(C59N) with a tubular host was oxidatively bisected to afford a C59N+ cation captured in the tube. The C59N+ cation in the tube was then trapped by ethanol or water, which led to an oxy substituent pinned on the guest. The guest motions within the tube were modulated by the pinned substituent, and up‐and‐down flipping motions were halted by an ethoxy substituent. A hydroxy substituent, however, was ineffective in halting the flipping motions, despite the tight‐fitting relationship between the tubular host and the spherical guest. Theoretical calculations of the dynamics revealed that the flipping motions were assisted by OH‐π hydrogen bonds between the guest and the carbon‐rich wall and that sliding motions of the OH group were also facilitated by deformations of the tube.  相似文献   

7.
Treatment of the open‐cage fullerene C63H4NO2(Ph)2(Py)(N2C6H4) ( 1 ) with methanol at 150 °C results in an orifice‐enlargement reaction to give C69H8NO(CO2Me)(Ph)(Py)(N2C6H4) ( 2 ). The overall yield from C60 to isolated 2 is 6.1 % (four steps). Compound 2 contains a 24‐membered elliptic orifice that spans 8.45 Å along the major axis and 6.37 Å along the minor axis. The skeleton of 2 resembles the hypothetic C60H10 (5,5)‐carbon nanotube endcap. The cup‐shaped structure of 2 is able to include water, hydrogen cyanide, and acetylene, forming H2O@ 2 , HCN@ 2 , and C2H2@ 2 , respectively. The molecular structures of H2O@ 2 and HCN@ 2 have been determined by X‐ray crystallography. The 1H NMR spectra reveal substantial upfield shifts for the endohedral species, such as δ=?10.30 (for H2O), ?2.74 and ?14.26 (for C2H2), and ?1.22 ppm (for HCN), owing to the strong shielding effects of the fullerene cage.  相似文献   

8.
Based on an experimental observation, it has been controversially suggested in a study (Kurotobi et al., Science 2011 , 33, 613) that a single molecule of water can completely be localized within the subnano‐space inside the fullerene C60 cage and, that neither the H atoms nor the O lone‐pairs are linked, either via hydrogen bonding or through dative bonding, with the interior C‐framework of the C60 cage. To resolve the controversy, electronic structure calculations were performed by using the density functional theory, together with the quantum theory of atoms in molecules, the natural population and bond orbital analyses, and the results were analyzed by using varieties of recommended diagnostics often used to interpret noncovalent interactions. The present results reveal that the mechanically entrapped H2O molecule is not electronically innocent of the presence of the cage; each H atom of H2O is weakly O? H???C60 bonded, whereas the O lone‐pairs are O???C60 bonded regardless of the conformations investigated. Exploration of various featured properties suggests that H2O@C60 may be regarded as a unique system composed of both inter‐ and intramolecular interactions.  相似文献   

9.
Novel difluoromethylenated [70]fullerene derivatives, C70(CF2)n (n=1–3), were obtained by the reaction of C70 with sodium difluorochloroacetate. Two major products, isomeric C70(CF2) mono‐adducts with [6,6]‐open and [6,6]‐closed configurations, were isolated and their homofullerene and methanofullerene structures were reliably determined by a variety of methods that included X‐ray analysis and high‐level spectroscopic techniques. The [6,6]‐open isomer of C70(CF2) constitutes the first homofullerene example of a non‐hetero [70]fullerene derivative in which functionalisation involves the most reactive bond in the polar region of the cage. Voltammetric estimation of the electron affinity of the C70(CF2) isomers showed that it is substantially higher for the [6,6]‐open isomer (the 70‐electron π‐conjugated system is retained) than the [6,6]‐closed form, the latter being similar to the electron affinity of pristine C70. In situ ESR spectroelectrochemical investigation of the C70(CF2) radical anions and DFT calculations of the hyperfine coupling constants provide evidence for the first example of an inter‐conversion between the [6,6]‐closed and [6,6]‐open forms of a cage‐modified fullerene driven by an electrochemical one‐electron transfer. Thus, [6,6]‐closed C70(CF2) constitutes an interesting example of a redox‐switchable fullerene derivative.  相似文献   

10.
A 14‐membered heterocycle is created on the C60 cage skeleton through a multistep procedure. Key steps involve repeated PCl5‐induced hydroxylamino N?O bond cleavage leading to insertion of nitrogen atoms, and also piperidine‐induced peroxo O?O bond cleavage leading to insertion of oxygen atoms. The hetero atoms form one pyrrole, two pyran, and one diazepine rings in conjunction with the C60 skeleton carbon atoms. The fullerene‐based macrocycle showed unique reactivities towards fluoride ion and copper salts.  相似文献   

11.
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.  相似文献   

12.
A new cluster fullerene, Sc2O@Td(19151)‐C76, has been isolated and characterized by mass spectrometry, UV/Vis/NIR absorption, 45Sc NMR spectroscopy, cyclic voltammetry, and single‐crystal X‐ray diffraction. The crystallographic analysis unambiguously assigned the cage structure as Td(19151)‐C76, which is the first tetrahedral fullerene cage characterized by single‐crystal X‐ray diffraction. This study also demonstrated that the Sc2O cluster has a much smaller Sc?O?Sc angle than that of Sc2O@Cs(6)‐C82 and the Sc2O unit is fully ordered inside the Td(19151)‐C76 cage. Computational studies further revealed that the cluster motion of the Sc2O is more restrained in the Td(19151)‐C76 cage than that in the Cs(6)‐C82 cage. These results suggest that cage size affects not only the shapes but also the cluster motion inside fullerene cages.  相似文献   

13.
The actinide endohedral fullerene Th@C76 was successfully prepared in a very recent experiment (Wang et al., J. Am. Chem. Soc. 2017 , 139, 5110) yet without any structural information. In this work, density functional theory calculations revealed that this novel molecule bears a Td(19151)‐C76 cage obeying the isolated pentagon rule. The internal Th atom is off‐centered and resides under a sumanene‐type hexagonal ring, formally donating 4e to the carbon cage. The metal position was rationalized by the structure and charge distribution of the negatively charged cage. Interestingly, an octahedron‐like dynamic trajectory of metal inside the C76 cage at high temperature was found based on the cage symmetry and located transition state structures. Furthermore, the infrared, NMR, and UV/vis spectra of Th@C76 were simulated to assist future experimental characterization.  相似文献   

14.
Although all fullerenes do not satisfy the classical aromaticity condition, as a result of their nonplanar nature, they experience effective stabilization due to extensive cyclic π‐electron delocalization and exhibit pronounced “spherical aromaticity”. This feature has raised the question of the opposite phenomenon, that is, the existence of antiaromatic carbon cages. Here the first experimental evidence of the existence of antiaromatic fullerenes is reported. The elusive #6094C68 was effectively captured as C68Cl8 by in situ chlorination in the gas phase during radio‐frequency synthesis. The chlorinated cage was separated by means of multistage HPLC, and its connectivity unambiguously determined by single‐crystal X‐ray analysis. Halogen‐stripped pristine #6094C68 was monitored by mass spectrometry of the chlorinated C68Cl8 cage. Quantum chemical calculations reveal the highly antiaromatic character of #6094C68, in accordance with all geometric, energetic, and magnetic criteria of aromaticity. Chlorine addition leads to substantial stabilization of the cage owing to aromatization in the resulting C68Cl8, which explains its high abundance in the primary fullerene soot. This work provides new insights into the process of fullerene formation and better understanding of aromaticity phenomena in general.  相似文献   

15.
A cobalt–porphyrin catalyst encapsulated in a cubic M8L6 cage allows cyclopropanation reactions in aqueous media. The caged‐catalyst shows enhanced activities in acetone/water as compared to pure acetone. Interestingly, the M8L6 encapsulated catalyst reveals size‐selectivity. Smaller substrates more easily penetrate through the pores of the “molecular ship‐in‐a‐bottle catalysts” and are hence converted faster than bigger substrates. In addition, N‐tosylhydrazone sodium salts are easy to handle reagents for cyclopropanation reactions under these conditions.  相似文献   

16.
A supramolecular complex was constructed by encapsulation of a 3O2 molecule inside an open‐cage C60 derivative. Its single‐crystal X‐ray diffraction analysis revealed the presence of the 3O2 at the center of the fullerene cage. The CV measurements suggested that unprecedented dehydrogenation was promoted by the encapsulated 3O2 after two‐electron reduction. The ESR measurements displayed the triplet character as well as the anisotropy of the 3O2. Additionally, the SQUID measurements also demonstrated the paramagnetic behavior above 3 K without an antiferromagnetic transition. Upon photoirradiation with visible light, three phosphorescent bands at the NIR region were observed, arising from the exited 1O2 generated by self‐sensitization with the outer cage, whose lifetimes were not affected by the environments. These studies confirmed that the complex is a crystalline triplet system with incompatible “high spin density” but “small interspin interaction” properties.  相似文献   

17.
Herein we show the synthesis and characterization of the second known Ce2@C80 isomer. A 13C NMR spectroscopic study revealed that the structure of the second isomer has D5h symmetry. Paramagnetic NMR spectral analysis and theoretical calculation display that the encapsulated Ce atoms circulate two‐dimensionally along a band of ten contiguous hexagons inside a D5h‐C80 cage, which is in sharp contrast to the three‐dimensional circulation of two Ce atoms in an Ih‐C80 cage. The electronic properties were revealed by means of electrochemical measurements. The D5h isomer of Ce2@C80 has a much smaller HOMO–LUMO gap than cluster fullerenes (M3N@C80, M=Sc, Tm, and Lu) with the same D5h‐C80 cages. The chemical reactivity was investigated by using disilirane as a chemical probe. The high thermal reactivity toward 1,1,2,2‐tetramesityl‐1,2‐disilirane is consistent with the trends of the redox potentials and the lower LUMO level of the D5h isomer of Ce2@C80 compared with that of C60.  相似文献   

18.
A supramolecular complex was constructed by encapsulation of a 3O2 molecule inside an open‐cage C60 derivative. Its single‐crystal X‐ray diffraction analysis revealed the presence of the 3O2 at the center of the fullerene cage. The CV measurements suggested that unprecedented dehydrogenation was promoted by the encapsulated 3O2 after two‐electron reduction. The ESR measurements displayed the triplet character as well as the anisotropy of the 3O2. Additionally, the SQUID measurements also demonstrated the paramagnetic behavior above 3 K without an antiferromagnetic transition. Upon photoirradiation with visible light, three phosphorescent bands at the NIR region were observed, arising from the exited 1O2 generated by self‐sensitization with the outer cage, whose lifetimes were not affected by the environments. These studies confirmed that the complex is a crystalline triplet system with incompatible “high spin density” but “small interspin interaction” properties.  相似文献   

19.
Water monomer and dimer encapsulations into D2(22)‐C84 fullerene are evaluated. The encapsulation energy is computed at the M06‐2X/6‐31++G** level, and it is found that the monomer and dimer storage in C84 yields an energy gain of 10.7 and 17.4 kcal mol?1, respectively. Encapsulation equilibrium constants are computed by using partition functions based on the M06‐2X/6‐31G** and M06‐2X/6‐31++G** molecular data. Under high‐temperature/high‐pressure conditions, similar to that for the encapsulation of rare gases in fullerenes, the computed (H2O)2@C84‐to‐H2O@C84 ratio is close to 1:2.  相似文献   

20.
Chlorination of C100 fullerene with a mixture of VCl4 and SbCl5 afforded C96Cl20 with a strongly unconventional structure. In contrast to the classical fullerenes containing only hexagonal and pentagonal rings, the C96 cage contains three heptagonal rings and, therefore, should be classified as a fullerene with a nonclassical cage (NCC). There are several types of pentagon fusions in the C96 cage including pentagon pairs and pentagon triples. The three‐step pathway from isolated‐pentagon‐rule (IPR) C100 to C96(NCC‐3hp) includes two C2 losses, which create two cage heptagons, and one Stone–Wales rotation under formation of the third heptagon. Structural reconstruction established C100 isomer no. 18 from 450 topologically possible IPR isomers as the starting C100 fullerene. Until now, no pristine C100 isomers have been confirmed based on the experimental results.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号