Chiral Calix[3]pyrrole Derivatives: Synthesis,Racemization Kinetics,and Ring Expansion to Calix[9]- and Calix[12]pyrrole Analogues

Chiral pyrrolic macrocycles continue to attract interest. However, their molecular design remains challenging. Here, we report a calixpyrrole-based chiral macrocyclic system, calix[1]furan[1]pyrrole[1]thiophene ( 1 ), synthesized from an oligoketone. Macrocycle 1 adopts a partial cone conformation in the solid state, and undergoes racemization via ring inversion. Molecular dynamics simulations revealed that inversion of the thiophene is the rate determining step. Pyrrole N-methylation suppressed racemization and permitted chiral resolution. Enantioselective N-methylation also occurred in the presence of a chiral ammonium salt, although the stereoselectivity is modest. A unique feature of 1 is that it acts as a useful synthetic precursor to yield several calix[n]furan[n]pyrrole[n]thiophene products (n=2–4), including a calix[12]pyrrole analogue that to our knowledge constitutes the largest calix[n]pyrrole-like species to be structurally characterized.     

Selective Encapsulation and Chiral Induction of C60 and C70 Fullerenes by Axially Chiral Porous Aromatic Cages

Chiral induction has been an important topic in chemistry, not only for its relevance in understanding the mysterious phenomenon of spontaneous symmetry breaking in nature but also due to its critical implications in medicine and the chiral industry. The induced chirality of fullerenes by host–guest interactions has been rarely reported, mainly attributed to their chiral resistance from high symmetry and challenges in their accessibility. Herein, we report two new pairs of chiral porous aromatic cages (PAC), R- PAC-2 , S- PAC-2 (with Br substituents) and R- PAC-3 , S- PAC-3 (with CH₃ substituents) enantiomers. PAC-2 , rather than PAC-3 , achieves fullerene encapsulation and selective binding of C₇₀ over C₆₀ in fullerene carbon soot. More significantly, the occurrence of chiral induction between R- PAC-2 , S- PAC-2 and fullerenes is confirmed by single-crystal X-ray diffraction and the intense CD signal within the absorption region of fullerenes. DFT calculations reveal the contribution of electrostatic effects originating from face-to-face arene-fullerene interactions dominate C₇₀ selectivity and elucidate the substituent effect on fullerene encapsulation. The disturbance from the differential interactions between fullerene and surrounding chiral cages on the intrinsic highly symmetric electronic structure of fullerene could be the primary reason accounting for the induced chirality of fullerene.     

[60]Fullerene-flavonoid dyads

A range of fullerene-chalcone, fullerene-flavone, and fullerene-chromone dyads, including a bis(flavonyl)-fullerene dyad, were prepared by 1,3-dipolar cycloaddition reactions of azomethine ylides to C₆₀ and by cyclopropanation of C₆₀ with flavonyl malonates. Synthetic and natural flavonoid derivatives were used as starting materials.     

[60]富勒烯的超分子自组装研究进展

超分子自组装是发展超分子电子学的重要途径。随着纳米科学和技术的迅速发展,自组装技术已成功地应用于纳米尺度物质的维数、形貌和功能等的调控。作为构筑分子水平上一维、二维、三维有序功能结构和高有序分子聚集态结构的关键技术,超分子自组装技术有力地推动了具有优良光、电、磁性能的分子材料和纳米功能材料更深层次的研究。本文综述了超分子自组装在富勒烯科学领域的基础研究和应用,特别是对有利于自组织和自组装功能的富勒烯基衍生物的设计与合成、超分子作用力引导的具有特定结构的分子体系的可控自组装、以及富勒烯分子聚集态结构材料的光物理过程、超分子中电子转移和能量转移现象进行了描述;并对卟啉、四硫富瓦烯、碗烯和杯芳烃等一系列富π电子化合物和大环主体分子等包含[60]富勒烯的主体化合物的超分子作用和超分自组装体以及通过氢键、π-π作用、静电力和范德华力和金属配位作用形成的[60]富勒烯超分子自组装体进行了总结,对未来发展进行了展望。     

Fullerenes Enclosed in Bridged Calix[5]arenes

Host systems that bind C ₇₀ preferentially to C ₆₀ are found in the bridged calix[5]arenes 1 (X= alkyne bridge). The complexation-induced shifts of the bound fullerene guests provide valuable information on the structure and dynamics of the supramolecular complex.     

Spectrophotometric study of the supramolecular complexes of [60]- and [70]Fullerenes with biscalix[6]arene and crown[4]calix[6]arene

[60]- and [70]Fullerenes have been shown to form 1:1 supramolecular complexes with bis[2-(5,11,17,23,29,35-hexa-tert-butyl-37,38,39,40,41-pentahydroxycalix[6]arenyl-oxy ethyl ether) (1) and 5,11,17,23,29,35-hexa-tert-butyl-37,38,40,41-tetra hydroxyl-39,42-(crown-4)calix[6]arene (2) in CHCl3 medium by electronic absorption spectroscopy. Formation constants (K) of the complexes of [60]- and [70]fullerenes with 1 and 2 have been determined at room temperature from which free energy of formation values of the complexes have been estimated. The very high formation constant value of [60]fullerene/1 complex (5900 dm3 mol-1) in indicative of formation of inclusion complex. Moreover, PM3 calculations reveal that intermolecular interaction between [60]fullerene and 1 proceeds through quite deep energy molecular orbital.     

Self-organization of amphiphilic [60]fullerene derivatives in nanorod-like morphologies

The aggregation of four charged C₆₀ derivatives has been investigated by TEM, SEM, and AFM microscopies. In all molecules a short aliphatic chain connects an ammonium cation to the fullerene sphere and the variation comes in the counter anions. In water, remarkably well-ordered structures that resemble nanorod-like aggregates are formed. They have a cross-sectional diameter and a length in the range of 30-60 and 100-900 nm, respectively. Fine topographical details were elucidated by atomic force microscopy, in which the height was found up to a maximum of 60 nm. Scanning electron microscopy shows that both the shape and morphology of the aggregates is consistent throughout the material. Nanorods of uniform shape were obtained with all molecules containing inorganic counter anions, BF₄⁻, Br⁻, and Cl⁻.     

Stereospecific Synthesis of Enantiopure [6]Helicene Containing a Seven-Membered Ring and [7]Helicene by Acid-Promoted Stepwise Alkyne Annulations of Doubly Axial-Chiral Precursors**

Enantiopure [6]helicene containing an embedded seven-membered ring and carbo[7]helicene (>99 % ee) with opposite helicity were simultaneously and quantitatively (>99 %) synthesized with a perfect stereospecificity through stepwise acid-promoted intramolecular alkyne annulations of doubly axial-chiral cyclization precursors. The helical handedness of the [6]- and [7]helicenes was fully stereocontrolled by the doubly axial chirality of the precursors as a result of complete axial-to-helical chirality transfer. The cyclizations proceeded in a stepwise manner; the first six-membered ring formation was followed by the kinetically controlled seven- or six-membered ring formation with or without helix-inversion of a [4]helicene intermediate generated during the first cyclization step, thus quantitatively producing enantiopure circularly polarized luminescent [6]- and [7]helicenes with opposite helicity.     

Reaction of [60]fullerene with CF3COOHal affords an unusual 1,3-dioxolano-[60]fullerene

Reaction of C₆₀ with acyl hypohalogenites CF₃COOBr or CF₃COOI in the presence of water affords an orthoester-type 1,3-dioxolanofullerene in 40-50% yield. This method cannot be applied for the synthesis of 1,3-dioxolanofullerenes bearing aryl- or alkyl-groups since they undergo non-selective halogenation under the reaction conditions.     

61-甲基-61-[12-(18-N-四氯邻苯二甲酰亚氨基)脱氢枞胺]-1,2-亚甲基富勒烯[60]的合成

以脱氢枞胺为原料,经氨基酰化、12位乙酰化、与对甲苯磺酰肼形成对甲苯磺酰腙衍生物,再通过卡宾中间体与C60进行[2+1]环加成反应合成了C60-脱氢枞胺衍生物。目标化合物经IR,UV-Vis,1H NMR,13C NMR,MALDI-TOF MS表征,所得化合物为[6,6]闭环结构C60加成产物。     

Synthesis and antioxidant activity of [60]fullerene-flavonoid conjugates

Chalcone, flavone, and arylideneflavanone derivatives bearing one or two 3,5-di-tert-butyl-4-hydroxyphenyl groups were synthesized from 2′,4′-dihydroxyacetophenone and 3,5-di-tert-butyl-4-hydroxybenzaldehyde. These flavonoids were converted into the corresponding malonates and then reacted with C₆₀ to yield the title compounds. The O-H bond dissociation enthalpies (BDE) and the chain-breaking antioxidant activity of the flavonoid derivatives and the corresponding C₆₀ conjugates were evaluated. These results are consistent with the phenolic moiety being the main responsible for the reaction with peroxyl radicals, while the C₆₀ part of the molecule acts synergically by trapping alkyl radicals under reduced O₂ partial pressure. These novel C₆₀-flavonoid conjugates are therefore promising leads for broad-spectrum radical scavengers.     

Inclusion of methano[60]fullerene derivatives in cavitand-based coordination cages

The X-ray study of self-assembled coordination cage 1, constituted of two tetrapyridyl-substituted resorcin[4]arene cavitands coupled through four square-planar palladium complexes is reported. The coordination cage, embracing an internal cavity of ca. 840 Å³, reveals to have the right size for the inclusion of large molecules such as fullerenes. Cage 1 forms 1:1 complexes with methano[60]fullerene derivatives 3 and 4 bearing a dimethyl and a diethyl malonate addend, respectively. Evidence for inclusion complexation was provided by ¹H NMR spectroscopic studies and ESI-MS investigations, which unambiguously showed the formation of 1:1 fullerene-cage complexes. The association constants (K_a) were experimentally determined to be ca. 150 M⁻¹ at 298 K in CD₂Cl₂. In both complexes 1·3 and 1·4, the malonate residue is threaded through one of the four lateral portals, as clearly shown by docking simulations.     

Energies of Charge Transfer for the Supramolecular Complexes of [60]- and [70]Fullerenes with a Series of meso-Tetraphenylporphyrins in the Solution State

Supramolecular complexes of [60]- and [70]fullerenes with various meso-tetraphenylporphyrins in toluene solutions have been studied by electronic absorption spectroscopy. Charge transfer (CT) absorption bands are observed in the visible region. Vertical ionization potentials (I _D ^V) of the meso-tetraphenylporphyrins are reported from a study of EDA interaction of these porphyrins with a number of electron acceptors like o-chloranil, p-chloranil, 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) and vitamin K. The dependence of the CT transition energy on the donor ionization potential has been utilized to estimate the vertical electron affinities (E _A ^V) of [60]- and [70]fullerenes in solution. The value of E _A ^V for [60]fullerene is found to be 0.10 eV lower in magnitude than that of [70]fullerene. We have extracted degrees of CT, and oscillator and transition dipole strengths of the fullerenes/meso-tetraphenylporphyrins complexes. The experimental results show that the CT complexes studied here have a neutral character in their ground states. Electronic coupling elements have been determined for fullerene/meso-tetraphenylporphyrin complexes. Values of the solvent reorganization energy indicate that the electron transfer process takes place at a faster rate in the case of [70]fullerene/meso-tetraphenylporphyrin complexes.     

C60 and C70 Compounds in the Pincerlike Jaws of Calix[6]arene

Isostructural species are found in the solid state for the supramolecular 1:2 complexes of a calix[6]arene molecule and either C₆₀ or C₇₀ (see the structure of the [(calix[6]arene)(C₆₀)₂] complex on the right). The calixarene assumes a double-cone conformation, and the overall structure is a result of the complementarity of the building blocks with respect to size and form—in other words, the shallow calixarene cavity and the fullerene surface have similar curvatures.     

Synthesis of Novel [1,2,4]triazolo[3,2-b][2,4,6]benzothiadiazocin-11(5H,10H)-One Derivatives

Several [1,2,4]triazolobenzothiadiazocin-11-ones 3 were prepared via ring expansion of [1,2,4]triazolo[3,2-b][2,4]benzothiazepin-10(5H)-ones 1 in presence of sodium azide. The reaction intermediate was isolated and characterized as an aryl isocyanate 2b . A possible pathway for formation of novel triazolobenzothiadiazocin-11-one 3 is described.     

Stability studies of an electrochemically formed [C60]fullerene-palladium two-component film

The stability of C₆₀ and palladium two-component films, C₆₀/Pd, has been investigated. The effect of different polymerization conditions on the electrochemical stability of the film upon prolonged potential cycling has been studied. Stable voltammetric behavior was observed for polymers formed at potentials less negative than the potential of third C₆₀ reduction step. The incorporation of palladium particles into the structure of C₆₀/Pd polymers increases the polymer stability. The C₆₀/Pd films are doped with supporting electrolyte cations during reduction. The size of these cations is a crucial factor in determining the stability of the film. A strong solvent effect on the potential stability of the film was also observed. The wildest range of stable voltammetric properties was found for acetonitrile and N,N-dimethylformamide. No effect of the temperature on the film stability was observed. The results reported in this work allow for the determination of the optimal conditions for the formation of stable C₆₀/Pd films.     

Liquid‐Crystalline Mixed [5 : 1]Hexa‐adducts of [60]Fullerene. Preliminary Communication

A liquid‐crystalline mixed [5 : 1]hexa‐adduct of [60]fullerene was synthesized by addition of two different malonate derivatives onto C₆₀. The hexa‐adduct derivative 2 was prepared by a stepwise synthetic procedure (fullerene→mono‐adduct of C₆₀→hexa‐adduct of C₆₀). Cyanobiphenyl and octyloxybiphenyl derivatives were selected as mesogens. The malonate derivatives showed either a monotropic nematic phase or a monotropic smectic A phase, and the hexa‐adduct derivative gave rise to an enantiotropic smectic A phase.     

Synthesis of [60]fullerene-based α-amino acid derivatives

N-(2-methyl-5,6,7,8-tetrahydro[60]fullero[1,2-g]quinazolin-4-yl)-α-amino acid derivatives were obtained by Diels-Alder addition of adequately substituted pyrimidine ortho-quinodimethanes to C₆₀. One of the new compounds is a l-lysine derivative were both the amino and the carboxyl groups are free; this compound is suitable to be incorporated in peptides.     

富勒烯(C60/70)-丙烯酸的自由基共聚

富勒烯及其衍生物在超导、光电、磁学等领域展现出奇特性能[1],富勒烯的化学修饰成为化学工作者们关注的热点之一,而其中合成含富勒烯的新型聚合物是一个非常重要的方面.