Reactivity of fullerene C<Subscript>60</Subscript>

The results of a quantum-chemical study of the reactivity of fullerene C₆₀ in such reactions as polymerization (dimerization), cycloaddition, addition of valence-saturated molecules are presented. The mechanisms of these reactions are also discussed.     

Aqueous dispersions of C<Subscript>60</Subscript> fullerene

Stable aqueous colloidal dispersions of C₆₀ fullerene are prepared. A solvatochromic effect is revealed upon the addition of C₆₀ solution in chlorobenzene to a water-acetone mixture.     

Synthesis of fullerene C<Subscript>60</Subscript> monoadducts. Cyclopropanation of C<Subscript>60</Subscript> with sulfonium ylides

3′H-Cyclopropa[1,9](C₆₀-I_h)[5,6]fullerene-3′-carboxylic acid can be synthesized in a good yield by cyclopropanation of fullerene C₆₀ with 2-(dimethyl-λ⁴-sulfanylidene)acetates provided that the ester residue is readily hydrolyzable in acid medium.     

Synthesis and structures of C<Subscript>60</Subscript> fullerene chlorides

Systematic study of chlorination of fullerene C₆₀ with inorganic chlorides SbCl₅, VCl₄, MoCl₅, and KICl₄ was carried out. Higher chlorofullerenes, viz., T _h -C₆₀Cl₂₄, C₆₀Cl₂₈, C ₂-C₆₀Cl₃₀, and D _3d -C₆₀Cl₃₀, can be prepared depending on the temperature and time of chlorination. The molecular and crystal structures of C₆₀Cl₂₄⋅VOCl₃, C₆₀Cl₃₀⋅2CS₂, and C₆₀Cl₃₀O_1.22 were determined by single-crystal X-ray diffraction. Fullerenes C₆₀Cl₂₈ and C ₂-C₆₀Cl₃₀ were shown to be only kinetically stable, whereas D _3d -C₆₀Cl₃₀ is a thermodynamically stable product. Transformations of less chlorinated fullerenes into more chlorinated products are accompanied by substantial changes in the addition patterns. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1608–1618, July, 2005.     

Direct phosphorylation of fullerene C<Subscript>60</Subscript> with phosphine

Fullerene C₆₀ reacts with phosphine (PH3) under free radical initiation conditions (azobis(isobutyronitrile), xylene, 65°C, 6–11 h) to give in the presence of air oxygen functional oligofullerenes (yield up to 32%) containing functional groups of phosphinic and phosphonic acids.     

The structural-phase state of C<Subscript>60</Subscript>-C<Subscript>70</Subscript> fullerene mixtures

The structural and phase state of the C₆₀-C₇₀ system at various C₆₀/C₇₀ ratios in mixtures obtained by the vaporization of solutions in toluene at ∼98°C was studied by X-ray structure analysis, differential scanning calorimetry, and infrared spectroscopy. Solid solutions based on the face-centered cubic packing of C₆₀ are not formed in the C₆₀-C₇₀ system at C₇₀ contents from 0.5 to 50 wt %. The hexagonal close packing of a solid solution of C₆₀ in C₇₀ can be formed as a result of the thermally activated decomposition of the ternary crystal solvate in the C₆₀-C₇₀-C₆H₅CH₃ system. The structural state of multiphase mixtures formed under conditions far from equilibrium is characterized by a high degree of structure imperfection and greater ability to undergo oxidation compared with C₆₀ and C₇₀.     

Kinetics and products derived from C<Subscript>60</Subscript> fullerene radiolysis in toluene

C₆₀ fullerene was radiolyzed in toluene solution both in presence of air and in vacuum at four different radiation doses 12, 24, 36, 48 and 96 kGy. Clear evidences of the addition of benzyl radicals to the fullerene cage derive from FT-IR and C¹³-NMR spectra of the reaction product. In presence of air the interference of oxygen is evident in the FT-IR spectra and from the elemental analysis. A detailed analysis of the kinetics of the multiple addition of benzyl radicals to the fullerene cage was made spectrophotometrically with the determination of the addition rate constants at the each addition step and the average number of benzyl groups added to the fullerene cage as function of the radiation dose.     

Covalent binding of fullerene C<Subscript>60</Subscript> to pharmacologically important compounds

The cycloaddition of diazo compounds derived from α-tocopherol, betulinic acid, ursolic acid, and Trolox methyl esters to fullerene C₆₀ in the presence of a Pd(acac)₂-PPh₃-Et₃Al catalytic system was performed. The reactions of the diazo compounds derived from the above-mentioned pharmacologically important compounds with fullerene C₆₀ in the presence of the Pd(acac)₂-PPh₃-Et₃Al system (1: 2: 4) afford predominantly the previously inaccessible pyrazolinofullerenes. A change in the component ratio of the Pd(acac)₂-PPh₃-Et₃Al catalyst from 1: 2: 4 to 1: 4: 4 favors the formation of methanofullerenes exclusively.     

Bis(Allyloxycarbonyl)methano derivatives of fullerene C<Subscript>60</Subscript>

Mono-, bis-, tris-, tetrakis-, and hexakis-substituted cyclopropanation products of fullerene C₆₀ with diallyl malonate were synthesized according to Bingel-Hirsch. Except for the monocyclopropanation product, all other adducts were isolated as mixtures of regioisomers.     

Thermodynamic properties of the molecular complexes of C<Subscript>60</Subscript>with monosubstituted naphthalenes

Summary The binary systems of C₆₀with α-methyl- and α-chloronaphthalene have been studied by means of differential scanning calorimetry. C₆₀was found to form the molecular complex of the van der Waals type with α-methylnaphthalene which melts incongruently below the boiling point of the solvent at temperature 382.7±3.0 K. The enthalpy of the desolvation reaction is 14.1±0.5 kJ mol^-1of C₆₀. The molar ratio of fullerene to solvent in the solvate is 1:1.5. In the system C₆₀-α-chloronaphthalene a two-stage incongruent melting process has been observed at temperatures 314.1±4.6 K and 375.7±7.4 K with the enthalpies 8.1±2.6 kJ mol^-1and 11.6±1.0 kJ mol^-1, respectively. The composition of the most solvated phase equilibrated with the saturated solution at room temperature and below the first of the incongruent melting transitions was determined as 1:1.5. Based on the results obtained the thermodynamic characteristics of the incongruent melting reactions have been revealed and influence of solvate formation on solubility of C₆₀has been discussed.     

Catalytic hydroamination of fullerene C<Subscript>60</Subscript> with primary and secondary amines

Catalytic 1,2-hydroamination of fullerene C₆₀ with primary and secondary amines in the presence of Ti, Zr, and Hf complexes gave the corresponding alkyl-, aryl-, and hetarylaminodihydrofullerenes.     

Nafion-based composite solid electrolytes containing water-soluble fullerene C<Subscript>60</Subscript> derivatives

Nafion-based composite solid polyelectrolytes containing fullerene C₆₀ and its water-soluble derivatives fullerenol-C₆₀ and tris-malonate-C60 were studied by the impedance spectroscopy method. It was found that introduction of these dopants in Nafion leads to a substantial increase in proton conductivity of the composites in the region of low relative humidity. The reasons for the influence of dopants on proton conductivity of composites were discussed.     

Self-assembling of fullerene C<Subscript>60</Subscript> into (C<Subscript>60</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> clasters in aromatic solvents

Self-assembling of fullerene C₆₀ into (C₆₀) _n clusters in aromatic solvents was studied. The role of the π-π interactions and dispersion forces in the (C₆₀) _n cluster formation in these media is demonstrated using the data on the solubility of fullerene C₆₀ in these solvents and their ionization potentials and also spectral characteristics of fullerene C₆₀ in the range of 326–340 nm in different solvents.     

Internal organization and conformational characteristics of star-shaped polystyrene with fullerene C<Subscript>60</Subscript> as a branching center in deuterotoluene

The internal organization of star-shaped polystyrene macromolecules containing fullerene C₆₀ as a branching center is studied via small-angle neutron scattering in deuterotoluene. Analysis of the experimental data according to the Debye-Benoit approximation and the Fourier transformation of the momentum transfer dependences of scattering cross sections for the linear PS precursor and stars is used to determine their molecular masses (9 × 10³ and 5 × 10⁴) and gyration radii (∼2.7 and ∼5.5 nm), the gyration radius of the arm (∼3.4 nm), and the average functionality of the star (5.7). The behavior of scattering cross sections for the fullerene-containing polymer on the whole is described by the law of scattering for stars with Gaussian arms (the Benoit model). However, at the local level (within one chain segment), the fullerene center exerts a specific effect on the conformation of arms. As a result, their statistical flexibility decreases and eventually the size of the star increases by ∼30%. This finding conflicts with the Daoud-Cotton theory.     

The thermodynamic properties of the [(Me<Subscript>3</Subscript>Si)<Subscript>7</Subscript>C<Subscript>60</Subscript>]<Subscript>2</Subscript> fullerene complex

The temperature dependence of the heat capacity C _p ^o of the [(Me₃Si)₇C₆₀]₂ fullerene complex was measured for the first time using precision adiabatic vacuum calorimetry over the temperature range 6.7–340 K and high-accuracy differential scanning calorimetry at 320–635 K. For the most part, the error in the C _p ^o values was about ±0.5%. An irreversible endothermic effect caused by the splitting of the dimeric bond between fullerene fragments and the thermal decomposition of the complex was observed at 448–570 K. The thermodynamic characteristics of this transformation were calculated and analyzed. Multifractal analysis of the low-temperature (T < 50 K) heat capacity was performed, and conclusions were drawn concerning the character of the heterodynamicity of the structure. The experimental data obtained were used to calculate the standard thermodynamic functions C _p ^o (T), H ^o (T) ? H ^o (0), S ^o (T) ? S ^o (0), and G ^o (T) ? H ^o (0) over the temperature range from T → 0 to 445 K and estimate the standard entropy of formation of the compound from simple substances at 298.15 K. The standard thermodynamic properties of [(Me₃Si)₇C₆₀]₂ are compared with those of the (C₆₀)₂ dimer, the [(η⁶-Ph₂)₂Cr]⁺[C₆₀]^?? fulleride, and the initial C₆₀ fullerene.     

The standard enthalpy of formation of fullerene chloride C<Subscript>60</Subscript>Cl<Subscript>30</Subscript>

A rotating-bomb calorimeter was used to measure the energy of combustion of crystalline fullerene chloride C₆₀Cl₃₀ · 0.09Cl₂, Δ_c U° = (?24474 ± 135 kJ/mol). The result was used to calculate the standard enthalpy of formation, Δ_f H° (C₆₀Cl₃₀, cr) = 135 ± 135 kJ/mol, and the C-Cl bond energy, 195 ± 5 kJ/mol. The C-X (X = F, F, Cl, and Br) bond energies in fullerene C₆₀ derivatives and other organic compounds are compared.     

Gas-separating properties of membranes based on star-shaped fullerene (C<Subscript>60</Subscript>)-containing polystyrenes

Based on regular star-shaped PSs differing in the structure of the branching center (one or two covalently bound fullerene C₆₀ molecules) and in the number of branchings (6 and 12), homogeneous gas-separation membranes have been produced. The transport behavior of the membranes with respect to several gases, such as H₂, He₂, N₂, CO, CO₂, and CH₄, has been studied by mass spectrometry. It has been found that the membranes prepared from six-arm PSs are characterized by a smaller density of macromolecular packing than the membranes obtained from 12-arm PCs and, consequently, they possess higher gas permeability. The starshaped PSs demonstrate a higher selectivity factor for separation of the O₂/N₂ gas pair compared to the corresponding characteristics of the linear PSs. The analysis of gas-separation characteristics by means of the Reitlinger-Robeson diagrams demonstrates that the transport behavior of star-shaped PSs qualitatively surpasses similar parameters of the known polymers in the separation of the CO/N₂ gas pair.     

Quantitative analysis of compression isotherms of fullerene C<Subscript>60</Subscript> Langmuir layers

The structure of fullerence C₆₀ Langmuir layers formed from a solution in cyclohexane has been determined from their compression isotherms. The layer structure, in particular, the size of formed aggregates, has been shown to depend on the initial surface concentration of fullerene. A quantitative model of the Langmuir layer has been proposed. Degrees of water surface coverage with fullerene (the initial one and that corresponding to the onset of one-phase state formation), intermolecular distances of fullerene in aquaaggregates, aggregation numbers, and distances between aquaaggregates have been found to play the role of the model parameters. Constants characterizing the structure of a stable monolayer have been determined on the basis of the formulated model.     

Catalytic cycloaddition of diazoalkanes with heterocyclic substituents to fullerene C<Subscript>60</Subscript>

Methanofullerenes were directly synthesized under mild conditions by cycloaddition to fullerene C₆₀ of diazoalkanes generated in situ by oxidation of ketone hydrazones containing a heterocyclic fragment with manganese(IV) oxide in the presence of the catalytic system Pd(acac)₂-2 PPh₃-4 Et₃Al.