Reactions of chlorofullerene C60Cl6 with N-substituted piperazines

It was shown for the first time that reactions of C₆₀ halides with aliphatic amines provide a facile route for the synthesis of aminofullerenes, valuable precursors for water-soluble cationic fullerene derivatives. Particularly, chlorofullerene C₆₀Cl₆ and N-substituted piperazines were investigated in this work. It was shown that substitution of chlorine atoms in C₆₀Cl₆ by amine groups is accompanied by partial elimination of addends from the fullerene cage that yields mixtures of di-, tetra- and, hexaaminofullerenes as the final products. Separation of these mixtures by column chromatography resulted in isolation of pure 1,4-diaminofullerenes; this procedure gives much higher and more reproducible yields of these compounds than direct oxidative photoaddition of secondary amines to C₆₀. ESI mass spectrometry and NMR spectroscopy data showed that hexaaminofullerene isomers are major components in inseparable mixtures of polyaddition products. Polyaminofullerenes were found to be readily soluble in aqueous acids; these solutions are unstable because of a facile substitution of protonated amine groups with hydroxyls. Nevertheless, the use of other amine substrates in the investigated reaction can potentially allow the preparation of more stable water-soluble cationic fullerene derivatives for biological studies.     

Variation of triplet state properties of N-mTEG[60]fulleropyrrolidine bis-adducts as a function of the bond path between the addends

For a group of seven isomeric N-mTEG[60]fulleropyrrolidine bis-adducts (mTEG = CH₂CH₂OCH₂CH₂OCH₂CH₂OCH₃), the quantum yields of singlet oxygen (O₂, ¹Δ_g) production and the maximum triplet molar absorption coefficients were found to be separately correlated with the shortest distances and with the number of bonds connecting the two addends on the fullerene sphere.     

Syntheses and crystal structures of azafulleroid and aziridinofullerene bearing silyl or germyl benzene

Addition of silyl and germylmethyl azides (1) to fullerene C₆₀ at 50 °C through [2+3] cycloaddition led to the formation of the triazoline adducts (2). Subsequently, heating 2 at 100 °C in the solid state, caused N₂ extrusion producing two different isomers, [5,6]-azafulleroid (3) and [6,6]-aziridinofullerene (4). The ¹³C NMR spectrum of 3 had an absence of resonances in the aliphatic region for the fullerene C₆₀ cage, showing a fulleroid with C_S symmetry. In contrast, 4 exhibited one sp³ resonance in the aliphatic region for the fullerene C₆₀ cage, indicative of an aziridinofullerene with C_2V symmetry. However, MALDI-TOF mass characterization was hampered because ion peaks corresponding to the bis-adduct are detected in positive ion mode measurements, whereas the ion peaks [M−N₂]⁻ for 2a as well as [M]⁻ for 3a and 4a are observed in negative ion measurements. In an effort to obtain X-ray data, silyl and germylphenyl groups were introduced to form intermolecular complexes with fullerene C₆₀. The X-ray structures of 3c and 3d revealed a strong enhancement of homoconjugation in the bridged annulene moiety based on POAV analysis. The X-ray structures of 3c,d and 4c were confirmed with the detection of silyl and germylphenyl-C₆₀ interactions, similar to dimethoxyphenyl-C₆₀ interactions.     

Cyclopentene-fused [C60]-fullerenes: synthesis and electrochemical properties

New cyclopentene-fused [C60]-fullerene derivatives containing terpene moieties have been synthesized by [3?+?2]-addition to fullerene C₆₀. All obtained products were fully characterized by ¹H- and ¹³C-NMR, IR, and MS. The electrochemical properties have been studied by cyclic voltammograms (CV), combined with absorption spectra, which are consistent with those obtained from density functional theory (DFT) calculations. It was found that all fulleropyrrolidines showed very similar absorption spectra, orbital energies, in which electron densities in both the LUMO and HOMO are mainly located on the fullerene cage, suggesting that C₆₀ act as the acceptor. All the compounds exhibited good thermal stability. All determined characteristics of fullerene conjugates were compared to [6,6]-phenyl-C61-butyric acid methyl ester ([60]PCBM), a popular fullerene-containing compound.

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Fullerene-Acetylene Molecular Scaffolding: Chemistry of 2-functionalized 1-ethynylated C60, oxidative homocoupling,hexakis-adduct formation,and attempted synthesis of C

On the way to the fullerene-acetylene hybrid carbon allotropes 2 and 6 , the oxidative homocoupling of the 2-functionalized 1-ethynylated C₆₀ derivatives 11, 12, 14 , and 15 was investigated. Under Glaser-Hay conditions, the two soluble dumbbell-shaped bisfullerenes 17 and 18 , with two C₆₀ moieties linked by a buta-1,3-diynediyl bridge, were formed in 52 and 82% yield, respectively (Scheme 2). Cyclic-voltammetric measurements revealed that there is no significant electronic communication between the two fullerene spheres via the buta-1,3-diynediyl linker. Removal of the 3,4,5,6-tetrahydro-2H-pyran-2-yl (Thp) protecting groups in 18 gave in 80% yield the highly insoluble dumbbell 19 with methanol groups in the 2,2′-positions of the buta-1,3-diynediyl-bridged carbon spheres. Attempted conversion of 19 to the all-carbon dianion 6 (C) via base-induced elimination of formaldehyde was not successful presumably due to exo-dig cyclization of the formed alkoxides. The occurrence of this cyclization under furan formation was proven for 2-[4-(trimethylsilyl)buta-1,3-diyn-1-yl][60]fullerene-1-methanol ( 21 ), a soluble model compound for 19 (Scheme 3). To compare the properties of ethynylated fullerene mono-adducts to those of corresponding higher adducts, hexakis-adducts 26 and 28 with an octahedral functionalization pattern resulting from all-e (equatorial) additions were prepared by the reversible-template method of Hirsch (Scheme 4). Reaction of the ethynylated mono-adducts 25 or 13 with diethyl 2-bromomalonate/1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in the presence of 1,9-dimethylanthracene (DMA) as reversible template led to 26 and 28 in 28 and 22% yield, respectively. Preliminary experiments indicated a significant change in reactivity and NMR spectral properties of the fullerene addends with increasing degree of functionalization.     

Sequential ortho effects: characterization of novel [M - 35]+ fragment ions in the mass spectra of 2-alkyl-4, 6-dinitrophenols

High-resolution mass spectrometry (HRMS), hybrid tandem mass spectrometry (MS/MS) (EBqQ), and photoelectron-photoion coincidence (PEPICO) experiments were conducted to examine a possible ortho-ortho effect resulting in a novel [M - 35]⁺ fragment ion in 2-alkyl-4, 6-dinitrophenols. For compounds having ethyl or larger alkyl substituents, [M35]⁺ was observed only when [M - 18]⁺ ions were present, with the ortho nitro group being involved in the reaction to [M- 35]⁺. For [M - 18]⁺ and [M - 35]⁺, HRMS results were consistent with losses of H₂O and H₂O + OH, respectively, whereas MS/MS results indicated a sequential reaction due to metastable dissociations. The appearance energy determined by PEPICO for [M - 35]⁺ was found to be greater than the appearance energy for [M - 18]⁺, thus supporting a sequential reaction. 69–75).     

Variations in functional substitution of the macroheterocycle and structure of stable rhenium(V) porphyrins

Rhenium(V) porphyrin complexes with different natures of substituents and substitution patterns in the organic fragment (5,10,15,20-tetraphenylporphyrin, 2,3,7,8,12,13,17,18-octaethylporphyrin, 2,3,7,8,12,13,17,18-octaethyl-5-phenylporphyrin, and 2,3,7,8,12,13,17,18-octaethyl-5,15-diphenylporphyrin dianions) and different axial ligands {phenoxide and chloride ions, 2′-(pyridin-4-yl)-5′-(pyridin-2-yl)-1′-(pyridin-3-ylmethyl)pyrrolidino[3′,4′: 1,9](C₆₀-I _h)[5,6]fullerene} have been synthesized, and their principal properties (spectral parameters and reactivity toward fullerene-containing base) have been studied.     

Electrochemical synthesis of carbonyl- and phosphoryl-containing methano[60]fullerenes

The combined electrochemical reduction of fullerene C₆₀ in the presence of p-bromo-benzoyldibromomethane or bis(diisopropoxyphosphoryl)dibromomethane at a brass electrode in a mixed solvent o-dichlorobenzene-MeCN (3:1 v/v)/0.05 M Bu₄NBF₄ at room temperature affords 61-(p-bromobenzoyl)methano[60]fullerene or 61,61-bis(diisopropoxyphosphoryl)methano[60]fullerene, respectively, in 50% yields.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2681–2685, December, 2004.     

Retro-Bingel reaction in the electrochemical reduction of bis(dialkoxyphosphoryl)methanofullerenes

Four steps of reduction were detected for bis(diethoxyphosphoryl)- and bis(diisopropoxyphosphoryl)methano[60]fullerenes (1, 2) and bis(diethoxyphosphoryl)methano[70]fullerene (3) by cyclic voltammetry in the o-dichlorobenzene—DMF (3 : 1, v/v)/Bu₄NBF₄ (0.1 mol L^–1) system on a glass-carbon electrode. At the first step the reversible transfer of one electron affords stable radical anions 1 and 2 (g = 1.9999, H = 1.9 G). When two electrons per molecule are transferred, the methano fragment is rapidly eliminated (retro-Bingel reaction). This process involves the step-by-step cleavage of two C—C bonds of exo-carbon with the fullerene shell in combination with the stepwise transfer of other two electrons and a proton to form finally the carbanion of the methano fragment and fullerene dianion. For all studied compounds, the elimination rate is much higher than that for bis(alkoxycarbonyl)- and dialkoxyphosphoryl(alkoxycarbonyl)methano[60]fullerenes, which makes it possible to propose bisphosphorylmethane groups as protective in synthesis of new fullerene derivatives.     

Synthesis of fullerene multiadducts with mixed oxygen and nitrogen addends including five secondary amino groups

The reaction of aminoketal[60]fullerene peroxide with pyrrolidine removes all the peroxo groups giving the aminooxahomo[60]fullerene derivatives with five amino addends together with one hydroxyl, one epoxy and three ether moieties. The structure has been determined by spectroscopic data and single crystal X-ray analysis.     

Novel open-cage fullerenes having a 12-membered-ring orifice: removal of the organic addends from the rim of the orifice

Two novel open-cage fullerene derivatives bearing a 12-membered-ring orifice on the fullerene cage have been isolated. Removal of the N-MEM protective group leads to the first open-cage [60]fullerene derivative without organic addends on the rim of the orifice. [structure: see text]     

Novel addition in trifluoromethylation of [70]fullerene

Pyrolytic trifluoromethylation of [70]fullerene with CF₃CO₂Ag at 300 °C results in the addition of up to 12 CF₃ groups to the fullerene cage. Forty-six C₇₀(CF₃)_n derivatives (numbers in parentheses) were separated by two-stage high pressure liquid chromatography (HPLC) as follows: n = 2(2), 4(16), 6(9), 8(14) 10(5), some being characterised by NMR. The range of derivatives is much greater than for other [70]fullerene reactions, and as with [60]fullerene trifluoromethylation, no single derivative is dominant, indicating that kinetic stability mainly controls product formation. NMR spectra show most derivatives to be unsymmetrical, with combinations of quartets and septets (overlapping quartets) due to contiguous (‘linear’) addend arrays, having significantly different coupling constants of the ‘terminal’ quartets of between 9.1 and 17.7 Hz. These differences, together with those observed previously in trifluoromethylation of [60]fullerene are consistent with addition across both 6:6- and 5:6-ring junctions. Of the two C₇₀(CF₃)₂ isomers, one has either C_s or C₂ symmetry, the other has C₁ symmetry, whilst the C₇₀(CF₃)₄ derivatives fall into four categories: (i) symmetrical compounds (one gives only two singlets in the NMR); (ii) unsymmetrical compounds that show a ‘linear’ coupling sequence; (iii) unsymmetrical compounds having a remote pairs of adjacent groups; (iv) compounds having a coupled array of three CF₃ groups, together with a remote group suggesting sterically-driven migration. The first evaluation of differential NMR couplings across 6:6- and 5:6-bonds in a fullerene has been made using C₆₀F₆ as a model.     

Complex formation between water-soluble sulfonated calixarenes and C60 fullerene

The inclusion complexes of sulfonated thiacalix[4]arene 1 and calix[6]arene 2 sodium salts with C₆₀ fullerene were investigated by photoluminescence (PL) and quantum-chemical methods. The stoichiometries of calixarene/C₆₀ complexes were found to be 2:1 for 1 and 1:1 for 2. Related quantum-chemical investigations show that C₆₀ fullerene is included in a cavity composed of two half-bowl molecules of 1. The C₆₀ fullerene ball is located deep within the cavity of 2 and the negatively charged sulfonate arms probably inhibit the formation of the bowl-shaped capsule that was observed in the case of 1.     

Amic acid complexes with aprotic polar solvents V. Complexes with amide solvents and isomerism of trimellite-dianilic acid

Complexes of trimellite-dianilic acid (TMA) with aprotic amide solvents have been sythetized, separated and investigated by TG and MTA methods. It was shown that the composition of these complexes is [TMA]₁ · [Sol]₁. The PMR spectra were used to show the ability of TMA to undergo isomeric transitions under mild conditions in an aprotic solvent.     

Synthesis of Octadecahydroxylated C70

Synthesis of novel hydrophilic [70]fullerenols was described. The reaction involved an oleum-induced oxidative sulfation of the C₇₀ molecules with a product yield of 86%. The rate of fullerene sulfation was accelerated either moderately or greatly by the addition of P₂O₅ or SeO₂, respectively. Hydrolysis of the resulting polycyclosulfated C₇₀ in H₂O at 80°C afforded [70]fullerenols in a yield of more than 72%. The negative ion MALDI-TOF mass spectrum of [70]fullerenols showed a well-defined pattern of ion fragmentations with a nearly constant, consecutive weight increase in 17 mass units from the mass of C₇₀. Detection of a molecular ion at m/z 1146 was indicative for the composition of [70]fullerenols as octadecahydroxyfullerenes, containing 18 hydroxy addends per C₇₀ cage. That correlates the structure of their polycyclosulfated precursors to nonacyclosulfated [70]fullerenes, C₇₀(SO₄)₉.     

Synthesis of Amphiphilic [60]Fullerene [3:3]Hexakisadducts with Four Spherically Defined Addend Zones

New [3:3]hexakisadducts 3 , 6 , and 7 have been synthesized by a stepwise addition of two tripodal malonate tethers to pristine [60]fullerene. For the first time, [3:3]hexakisadducts of two sets of asymmetrically substituted malonate addends could be prepared as single in/out isomers by following this synthetic protocol. Thereby, four spherically defined addend zones I–IV were created with various similar degrees of latitude on the fullerene sphere. Four amphiphilic [3:3]hexakisadducts 12 , 14 , 18 , and 19 were prepared with different relative arrangements of both the hydrophilic and lipophilic moieties in the addend zones I / II and III / IV , respectively.     

Effect of fullerene C60 as a branching center on molecular and polarization properties of star-shaped polystyrenes

The behavior of molecules of a star-shaped six-arm polystyrene with a covalently bound fullerene C₆₀ as a branching center was studied by viscometry and by measuring the electrooptical Kerr effect and the dielectric polarization in solutions. It was shown that polarization and electrooptical characteristics of a fullerene-containing polystyrene (C₆₀ ～ 3 wt %) differ by an order of magnitude or even greater from the corresponding characteristics of the parent polymer. A comparison of the above properties with the analogous characteristics of the model hexaadduct (the products of reaction between octyllithium and fullerene C₆₀) demonstrated that a difference in the behavior of the star-shaped polystyrene and its parent analog is associated with the structural features of the branching center, among which is the occurrence of six proton addends that are bonded rather weakly to the fullerene cage in the hexaadducts under study.     

Cycloaddition of C60 fullerene to stable 2-RSO2-benzonitrile oxides

The interaction of stable 2-RSO₂-benzonitrile oxides1a−c (R=Ph, Bu^t, or PhMeN) with C₆₀ fullerene proceeds at the double (6,6)-bond of fullerene as the [3+2] cycloaddition to form the corresponding isoxazolines2a−c. The molecular structure of compound2b was established by X-ray structural analysis. The interaction of C₆₀ fullerene with 2-(5-methyl-4-nitrothiophene)carbonitrile sulfide, which was obtained by thermolysis of 5-(5′-methyl-4′-nitro-2′-thienyl)1,3,4-oxathiazol-2-one, affords only unstable products. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 118–126, January, 1997.     

Mass Spectrometry Studies of the Retro-Cycloaddition Reaction of Pyrrolidino and 2-Pyrazolinofullerene Derivatives Under Negative ESI Conditions

Substituted pyrrolidino- and 3-alkyl-2-pyrazolinofullerenes ionize under ESI and MALDI mass spectrometry conditions and negative mode of detection undergoing mass spectral fragmentations, which can be easily correlated with the reported results for the thermal and electrochemical retro-cycloaddition reactions of these compounds. 2-Pyrazolinofullerenes lead directly to a [60]fullerene product ion formed through a retro-cycloaddition process regardless of the substituents attached at the carbon and nitrogen atoms of the heterocyclic ring. These results are different from whose reported for the thermal and electrochemical processes. In contrast, pyrrolidinofullerenes undergo different fragmentative reactions depending upon the substituents (hydrogen, alkyl, or acyl) attached at the nitrogen atom of the heterocyclic ring leading eventually to the pristine C₆₀ in the last step of the fragmentation pathway.