La@C72 having a non-IPR carbon cage

We show here that La@C72 has a non-IPR cage, unique electronic properties, and high reactivity by the spectroscopic and X-ray crystallographic analysis and the theoretical study. The isolation of La@C72 as a stable derivative might constitute an important stepping-stone on the way to isolation of these unknown metallofullerenes and open new material science of metallofullerenes.     

Radical coupling reaction of paramagnetic endohedral metallofullerene La@C82

The thermal reaction of La@C(82)(C(2v)) with 3-triphenylmethyl-5-oxazolidinone (1) in toluene affords benzyl monoadducts La@C(82)(C(2v))(CH(2)C(6)H(5)) (2a-2d). The same monoadducts are also obtained by the photoirradiation of La@C(82)(C(2v)) in toluene without the existence of 1. These reactions are applicable to paramagnetic metallofullerenes, such as La@C(82)(C(s)) and Ce@C(82)(C(2v)). The photoirradiation of La@C(82)(C(2v)) in 1,2-dichlorobenzene in the presence of alpha,alpha,2,4-tetrachlorotoluene also affords the monoadducts La@C(82)(C(2v))(CHClC(6)H(3)Cl(2)) (3a-3d). The monoadducts are fully characterized by spectroscopic analyses. Single-crystal X-ray structure analysis for 3d reveals the unique structure. Theoretical calculations show that the cage carbons having high spin densities are selectively attacked by radical species to form the monoadducts linked by a carbon-carbon single bond. The thermal reaction of La@C(82)(C(2v)) with 1 in benzene affords metallofulleropyrrolidine La@C(82)(C(2v))(C(2)H(4)NCPh(3)) (5), unlike the reaction in toluene.     

笼内金属富勒烯的合成与分析

自1985年,Smalleyr等人首次在飞行时间质谱仪中检测到C60以来,富勒烯碳原子族的研究便不断深入,最初发现的激光蒸发含稀土化合物的石墨只能得到微量的金属富勒烯,仅限于质谱检测,直到1990年,Kratschmer等人采用石墨电子弧放电首次得到宏观量的富勒烯,才使得富勒烯研究进入了实质性的研究阶段。富勒烯及其化合物的分子结构确定对于研究这类化合物无疑是非常重要的,红外光谱、核磁共振、X射线衍射、质谱以及电化学方法都是非常重要的手段。在富勒烯研究中,质谱是相当重要的,在80年代中期的富勒烯以及富勒烯衍生物如金属富勒烯多面体都在质谱中首次发现的。电弧法成功地得到富勒烯后,质谱因其灵敏度高、用量少、简便、快速等优点,成为富勒烯化合物物理化学性能研究以及结构表征工具,其中激光解吸电离为软电离技术只给出化合物分子质量而不产生碎片离子,已成为研究富勒烯首选的重要工具。     

Structural study of three isomers of Tm@C(82) by (13)C NMR spectroscopy

The (13)C NMR spectra were measured for three isomers of Tm@C(82), which is one of the divalent metallofullerenes. The molecular symmetries were determined for each isomer: isomer I has C(s) symmetry, isomer II has C(2) symmetry, and isomer III has C(2v) symmetry. Moreover the cage structure of Tm@C(82)(III) was found to be C(82)(9). As a result, it was revealed that Tm@C(82)(III) has a cage identical to that of La@C(82), which is one of the trivalent metallofullerenes.     

Host-guest complexation of endohedral metallofullerene with azacrown ether and its application

Complexation of endohedral metallofullerene La@C(82)-A (1) with macrocyclic compounds, such as 1,4,7,10,13,16-hexaazacyclooctadecane (2), 1,4,7,10,13,16-hexamethyl-1,4,7,10,13,16-hexaazacyclooctadecane (3), mono-aza-18-crown-6 ether (4), 18-crown-6 ether (5), and p-tert-butylcalix[n]arenes (n = 4-8, 6-10), for the first time is examined. Among them, 1 forms a complex with azacrown ethers 2-4 while accompanying the electron transfer between them. This is characteristic of endohedral metallofullerene and caused by its low reduction potential. Activation energies, DeltaG(et), for the electron transfer from 2-4 to 1 are 4.6, 2.8, and 11 kcal/mol, respectively. These small DeltaG(et) values indicate that the electron transfer from the azacrown ethers to 1 is facile in the ground state. Furthermore, the selective isolation of lanthanum endohedral metallofullerenes from the extracts of soot is accomplished by utilizing the complexation of 1 with 2.     

Isolation and characterization of carbene derivatives of La@C82(Cs)

The photochemical reaction of La@C82(Cs) with 2-adamantane-2,3-[3H]-diazirine (1) affords the adduct 2 of La@C82(Cs) with adamantylidene (Ad:) in a high selectivity. The two isomers of La@C82(Cs)(Ad), 2a and 2b, are isolated by HPLC and characterized by electron spin resonance, mass, and UV-vis-near-infrared spectroscopies. The electronic properties of 2a and 2b are very similar to that of the pristine La@C82(Cs), suggesting that 2a and 2b retain the essential electronic and structural character of La@C82(Cs).     

两步法提取笼内金属富勒烯

两步法提取笼内金属富勒烯郝春雁，刘子阳，徐文国，郭兴华，刘淑莹（中国科学院长春应用化学研究所，吉林大学化学系，长春，１３００２２）关键词金属富勒烯，索氏提取，ＤＥＩ－ＭＳ，ＬＤＩ－ＭＳ目前笼内包含金属的富勒烯化合物以其新颖独特的结构和性质而格外引人注...     

Convenient methods for the synthesis of highly functionalized and naturally occurring chiral allenes

A convenient two step procedure to access highly functionalized chiral allenes using chiral N-methylcamphanyl piperazine derivatives is described. In this transformation, chiral propargylamines are obtained in 79–96% yields with up to 99:1 dr by the CuBr catalyzed reactions of chiral piperazine derivatives with 1-alkynes and aldehydes containing functional groups, which are converted into chiral allenes in the presence of zinc bromide, affording the chiral allenes in 59–85% yields and with up to 99% ee. The antifungal agent Sapium japonicum and an allene precursor intermediate for the synthesis of the pheromone of the male dried bean beetle 15 are obtained in 72–78% yields and with up to 98% ee following this methodology.     

Ferromagnetic spin coupling between endohedral metallofullerene La@C82 and a cyclodimeric copper porphyrin upon inclusion

The cyclic host cyclo-[P(Cu)](2) carrying two covalently connected Cu(II) porphyrin units can accommodate La@C(82), a paramagnetic endohedral metallofullerene, in its cavity to form the inclusion complex cyclo-[P(Cu)](2)?La@C(82), which can be transformed into the caged complex cage-[P(Cu)](2)?La@C(82) by ring-closing olefin metathesis of its side-chain olefinic termini. On the basis of electron spin resonance (ESR) and electron spin transient nutation (ESTN) studies, cyclo-[P(Cu)](2)?La@C(82) is the first ferromagnetically coupled inclusion complex featuring La@C(82), whereas cage-[P(Cu)](2)?La@C(82) is ferrimagnetic.     

From MOF-74-Zn to Triazolate-Directed Nonsymmetric Assembly of Chiral Zn6@Zn6 Clusters

The creation of new cluster building blocks, as well as new ligand coordination modes, are among the most effective ways to develop new framework materials. Yet, large and chiral clusters are both difficult to create and relatively few. Here, by studying the competing coordination of different azolates against carboxylate and combined carboxylate/phenolate, it is shown that the impact of azolates in the MOF-74 synthesis system differs dramatically, leading to the synthesis of MOF-74, UTSA-74, and CPM-72 for 2-methylimidazole, 1,2,4-triazole, and 1,2,3-triazole, respectively. The new CPM-72 contains a novel chiral Zn₁₂ triazolate cluster, which features a trigonal-prismatic Zn₆ core inside an octahedral Zn₆ shell. In contrast with MOF-74 with fully deprotonated and symmetrically bonded 2,5-dihydroxyterephthalic acid (H₄DOBDC), H₄DOBDC adopts an unusual nonsymmetric bonding mode in CPM-72 (carboxylate only at one end and carboxylate/phenolate at the other), resulting in a highly porous and intrinsically chiral 3D framework. The nonsymmetric bonding mode by H₄DOBDC, apparently dictated by the chiral Zn₁₂ cluster, can be replicated with 2-hydroxyterephthalic acid (H₃OBDC), leading to the synthesis of porous isoreticular CPM-73.     

Spin-site exchange system constructed from endohedral metallofullerenes and organic donors

Complexation behavior of the paramagnetic La@C82 metallofullerene with organic donor molecules (D) in solution is investigated. It is revealed that La@C82 and D form a 1:1 complex as a result of electron transfer. La@C82 and D are in equilibrium with [La@C82]-/[D]*+ in solution, which is readily controllable by changing the temperature and solvent.     

Chemical understanding of a non-IPR metallofullerene: stabilization of encaged metals on fused-pentagon bonds in La2@C72

Fullerenes violating the isolated pentagon rule (IPR) are only obtained in the form of their derivatives. Since the [5,5]-bond carbons are highly reactive, they are easily attacked by reagents to release the bond strains. Non-IPR endohedral metallofullerenes, however, still have unsaturated sp (2) carbons at the [5,5] bond junctions, which allow their chemical properties to be probed. In this work, La 2@C 72 was chosen as a representative non-IPR metallofullerene, since it has been experimentally proposed to have either the #10611 or #10958 non-IPR cage structure ( J. Am. Chem. Soc. 2003, 125, 7782 ), while theoretical calculations have suggested that the #10611 cage is more stable ( J. Phys. Chem. A 2006, 110, 2231 ). La 2@C 72 was modified by photolytic reaction with the carbene reagent 2-adamantane-2,3-[3H]-diazirine. Six isomers of adamantylidene monoadducts were isolated and characterized using various kinds of measurements, including high-performance liquid chromatography, matrix-assisted laser desorption ionization mass spectrometry, UV-vis-near-infrared spectroscopy, cyclic voltammetry, differential-pulse voltammetry, (13)C NMR spectroscopy, and single-crystal X-ray diffraction. Electronic spectra and electrochemical studies revealed that the essential electronic structures of La 2@C 72 are retained in the six isomers and the adamantylidene group acts as a weak electron-donating group toward La 2@C 72. X-ray structural results unambiguously elucidated that La 2@C 72 has the #10611 chiral cage (i.e., D 2 symmetry) with two pairs of fused pentagons at each pole of the cage and that the two La atoms reside close to the two fused-pentagon pairs. On the basis of these results and theoretical calculations, it is concluded that the fused-pentagon sites are very reactive toward carbene but that the carbons forming the [5,5] junctions are less reactive than the adjacent ones; this confirms that these carbons interact strongly with the encaged metals and thus are stabilized by them.     

Effective procedure for selective ammonolysis of monosubstituted oxiranes: application to E7389 synthesis

A highly effective procedure is reported to synthesize 1,2-aminoalcohols by regio- and chemo-selective ammonolysis of mono-substituted epoxides. Additive- and concentration-effects were studied, revealing that (1) methanesulfonic acid is most effective among the additives tested and (2) formation of bis-adducts is practically eliminated at [C] ? 40 mM. The optimum condition thus identified was successfully applied to the final step of the synthesis of potent anti-tumor compound E7389.     

Nitrenoid from Oxime: A Practical Synthesis of Planar Chiral Ferrocenyl Phenanthridines via Nitrene-Involved Ring-Expansion Reaction

Nitrenes and nitrenoids are highly reactive species and the proposed key intermediates in nitrogen-containing heterocyclic compound synthesis. In this work, we developed a practical method for the synthesis of phenanthridines by the reaction of oximes and Grignard reagents (with or without diethylzinc) via ring-expansion of magnesium coordinated nitrenoid complex as the key step. The method has been used to synthesize optically active planar chiral ferrocenyl phenanthridines.     

Selective electrolytic removal of bis(alkoxycarbonyl)methano addends from C60 bis-adducts and electrochemical stability of C70 derivatives

The novel mixed bis-adducts of C60, (+/-)-4-(+/-)-8 and 9, with a bis(ethoxycarbonyl)methano addend (Bingel addend) and a second addend ([1,2]benzeno, but[2]eno, methaniminomethano, or diarylmethano) bridging 6,6-closed bonds of the carbon sphere were synthesized in two-step reactions. Each bis-adduct was exhaustively electrolyzed at the potential of the second fullerene-centered reduction step, resulting in the selective removal of the Bingel addend (retro-Bingel reaction) to produce the corresponding mono-adducts, which were isolated in yields of over 60%. These results open up the possibility of using the Bingel addend as a temporary protecting and directing group in the construction of multiple adducts of C60 with unusual addition patterns. The Bingel-type mono-adduct of C70 10 and the constitutionally isomeric bis-adducts 11, (+/-)-12, and (+/-)-13 were also included in this investigation. A large difference in the electrochemical behavior between C70 bis-adducts and the corresponding C60 derivatives was observed. Thus, the intramolecular "walk-on-the-sphere" isomerization which occurs readily with Bingel-type bis-adducts of C60 under the conditions of two-electron controlled potential electrolysis (CPE) is only a minor reaction pathway in the series of C70 derivatives. The latter preferentially undergo retro-Bingel reaction.     

X-ray Crystallographic Characterization of New Soluble Endohedral Fullerenes Utilizing the Popular C(82) Bucky Cage. Isolation and Structural Characterization of Sm@C(3v)(7)-C(82), Sm@C(s)(6)-C(82), and Sm@C(2)(5)-C(82)

Three isomers of Sm@C(82) that are soluble in organic solvents were obtained from the carbon soot produced by vaporization of hollow carbon rods doped with Sm(2)O(3)/graphite powder in an electric arc. These isomers were numbered as Sm@C(82)(I), Sm@C(82)(II), and Sm@C(82)(III) in order of their elution times from HPLC chromatography on a Buckyprep column with toluene as the eluent. The identities of isomers, Sm@C(82)(I) as Sm@C(s)(6)-C(82), Sm@C(82)(II) as Sm@C(3v)(7)-C(82), and Sm@C(82)(III) as Sm@C(2)(5)-C(82), were determined by single-crystal X-ray diffraction on cocrystals formed with Ni(octaethylporphyrin). For endohedral fullerenes like La@C(82), which have three electrons transferred to the cage to produce the M(3+)@(C(82))(3-) electronic distribution, generally only two soluble isomers (e.g., La@C(2v)(9)-C(82) (major) and La@C(s)(6)-C(82) (minor)) are observed. In contrast, with samarium, which generates the M(2+)@(C(82))(2-) electronic distribution, five soluble isomers of Sm@C(82) have been detected, three in this study, the other two in two related prior studies. The structures of the four Sm@C(82) isomers that are currently established are Sm@C(2)(5)-C(82), Sm@C(s)(6)-C(82), Sm@C(3v)(7)-C(82), and Sm@C(2v)(9)-C(82). All of these isomers obey the isolated pentagon rule (IPR) and are sequentially interconvertable through Stone-Wales transformations.     

Purification of endohedral trimetallic nitride fullerenes in a single, facile step

A major hurdle hampering the development of fullerenes, endohedral metallofullerenes, and nanotubes has been the difficulty of obtaining high purity samples. Soots prepared in the usual manner via a Kr?tschmer-Huffman electric-arc generator consist of mixtures of insoluble carbonaceous materials and soluble fullerenes: C60, C70, C76, C78, C84, etc. When metals are introduced as endohedral species the complexity of the resultant soot is even greater because of the presence of multiple isomers of both the empty fullerenes and the endohedral metallofullerenes. Here, for the first time, we report that lanthanide trimetallic nitride endohedral metallofullerenes, A3N@C80 (A = lanthanide atom, e.g., Er, Gd, Ho, Lu, Sc, Tb, Tm, Y), can be obtained in pure form directly from as-prepared soots in a single facile step by taking advantage of their extraordinary kinetic chemical stability with respect to the other fullerenes in Diels-Alder reactions with a cyclopentadiene-functionalized resin. We show that careful control of conditions (stoichiometry, time, temperature) allows separation of fullerenes with different cage sizes, as well as isomeric species. Furthermore, the Diels-Alder reaction is thermally reversible, and we demonstrated that the bound empty-cage fullerenes and classical endohedral metallofullerenes can be recovered by displacement with maleic anhydride.     

Ring-closure reactions through intramolecular substitution of thiophenoxide by oxygen and nitrogen nucleophiles: simple stereospecific synthesis of 4,5-dihydroisoxazoles and 4,5-dihydropyrazoles

A new and simple method for the stereospecific synthesis of 3,5-disubstituted-4,5-dihydro-isoxazoles (chiral isoxazolines) from readily available oximes of chiral Michael adducts of thiophenol to chalcones is reported. An analogous reaction with the N-arylhydrazones of the Michael adduct gave nonracemic 1-(aryl)-3,5-diphenyl-4,5-dihydro-1H-pyrazoles (chiral pyrazolines), but these products are configurationally unstable. The key step of the synthesis is the ring-closure reaction, which occurs by a stereospecific intramoleculer nucleophilic substitution of thiophenoxide.     

Achiral and Chiral Higher Adducts of C70 by Bingel Cyclopropanation

Five optically active isomeric C₇₀ bis-adducts with (R)-configured chiral malonate addends were prepared by Bingel cyclopropanation (Scheme 1) and their circular dichroism (CD) spectra investigated in comparison to those of the corresponding five bis-adducts with (S)-configured addends (Fig. 2). Pairs of diastereoisomers, in which the inherently chiral addition patterns on the fullerene surface have an enantiomeric relationship, display mirror-image shaped CD spectra that are nearly identical to those of the corresponding pairs of enantiomers (Fig. 3, b and c). This result demonstrates that the Cotton effects arising from the chiral malonate addends are negligible as compared to the chiroptical contribution of the chirally functionalized fullerene chromophore. A series of four stereoisomeric tetrakis-adducts (Fig. 4) was prepared by Bingel cyclopropanation starting from four stereoisomeric bis-adducts. A comparison of the CD spectra of both series of compounds showed that the magnitude of the Cotton effects does not decrease with increasing degree of functionalization (Fig. 5). Bingel cyclopropanations of C₇₀ in Me₂SO are dramatically faster than in apolar solvents such as CCl₄, and the reaction of bis-adducts (±)- 13 and 15 with large excesses of diethyl 2-bromomalonate and DBU generated, via the intermediacy of defined tetrakis-adducts (±)- 16 and 17 , respectively, a series of higher adducts including hexakis-, heptakis-, and octakis-adducts (Table 1). A high regioselectivity was observed up to the stage of the hexakis-adducts, whereas this selectivity became much reduced at higher stages of addition. The regioselectivity of the nucleophilic cyclopropanations of C₇₀ correlates with the coefficients of the LUMO (lowest unoccupied molecular orbital) and LUMO+1 at the positions of preferential attack calculated by restricted Hartree-Fock – self-consistent field (RHF-SCF) methods (Figs. 9 – 11). Based on predictions from molecular-orbital calculations (Fig. 11) and the analysis of experimental ¹³C-NMR data (Fig. 7, a), the structure of a unique hexakis-adduct ((±)- 22 , Fig. 12), prepared from (±)- 13 , was assigned. The C₂-symmetrical compound contains four 6−6-closed methanofullerene sub-structures in its polar regions (at the bonds C(1)−C(2), C(31)−C(32), C(54)−C(55), and C(59)−C(60)), and two 6−5-open methanofullerene sub-structures parallel to the equator (at C(22)−C(23) and C(26)−C(27)). The 6−5-open sub-structures are formed by malonate additions to near-equatorial 6−5 bonds with enhanced LUMO coefficients, followed by valence isomerization (Fig. 12).     

Enantioselective total synthesis of erogorgiaene: applications of asymmetric Cu-catalyzed conjugate additions of alkylzincs to acyclic enones

The first enantioselective synthesis of erogorgiaene (1), an inhibitor of mycobacterium tuberculosis, is disclosed. The total synthesis highlights the utility of asymmetric conjugate additions (ACA) of alkylzincs to acyclic alpha,beta-unsaturated ketones catalyzed by peptidic phosphine ligands and (CuOTf)(2).C(6)H(6). Moreover, several critical attributes of this catalytic C-C bond-forming reaction are illustrated in the context of the total synthesis; these include the significance of various structural features of the amino acid-based chiral ligands and the chiral ligand's effectiveness in reactions involving achiral and chiral substrates. In addition, the total synthesis showcases some of the special properties of nonphosphine Ru complex 3 as a highly effective catalyst for olefin cross-metathesis.