Synthesis and electrochemical properties of fullerene-containing C<Subscript>60</Subscript>-acceptor dyads with fluoronitrobenzene and fluoroquinoxaline moieties as substituents

Reactions of fullerene C₆₀ with 4-azido-3-fluoro-1-nitrobenzene and 7-azido-6-fluoroquinoxaline afforded earlier unknown cycloadducts (C₆₀-acceptor dyads), in which the electron affinities of the fullerene spheres are comparable with the affinity of nonmodified C₆₀.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 650–655, March, 2005.     

Quenching excited triplet C60 fullerene by tetracyanoethylene in benzonitrile

Quenching excited triplet³C₆₀ fullerene by tetracyanoethylene (TCNE) in a benzonitrile solution proceeds with a rate constant equal to (4.2±0.3) · 10¹⁸ (M · s)^–1. The formation of a radical ion pair [C₆₀ ⁺ · · · TCNE^–] was observed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1228–1230, July, 1993.     

Spectra of optical phonons and low-energy electronic transitions in C60/TMPD and C60/TPA single crystals

Single Crystals of C₆₀/TMPD and C₆₀/TPA have been grown from a chlorobenzene solution. Optical transmission spectra of single crystals of fullerene complexes withN,N,N,N-tetramethyl-p-phenylenediamine (TMPD) and triphenylamine (TPA) are studied in the spectral range from 600 to 16000 cm^–1. Splitting of the intramolecular vibration of C₆₀ is observed at 1428 cm^–1, which is likely caused by freezing of the rotation of the C₆₀ molecules due to their interaction with amines. Single crystals of C₆₀/TMPD differ from those of C₆₀/TPA by a decrease in the vibration frequency at 1428 cm^–1, vibrations of the C-C bonds of the TMPD molecule, and the redistribution of the forces of the oscillators of the vibrations of the C-N bonds. These peculiarities are interpreted to be the result of partial electron transfer from TMPD to C₆₀ in the C₆₀/TMPD single crystals. The electron transfer in the C₆₀/TPA system is less pronounced.Translated fromIzvestiya akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1459–1464, June, 1996     

The dichloromethane induced fragmentation of ferrocenylmethyldimethylamine. Mechanistic aspects and crystallographic and electrochemical investigation of the (FcCH2)2NMe2 and FcCH2NMe2H ions

Ferrocenylmethyldimethylamine, FcCH₂NMe₂, reacts with CH₂Cl₂ in either the presence or absence of non-coordinating counterions to give equimolar amounts of the bis(ferrocenylmethyl)dimethyl ammonium salts (FcCH₂)₂NMe₂⁺X⁻ (X⁻=PF₆⁻, SbF₆⁻, BPh₄⁻ or Cl⁻, 1a–d) and the corresponding protonated ammonium salts FcCH₂NMe₂H⁺ which have been isolated as the SbF₆⁻ and Cl⁻ salts 2b,d. The reaction proceeds via fragmentation of an intermediate quaternary chloromethylated ammonium ion to chloromethylferrocene, FcCH₂Cl, and dimethyliminium chloride NMe₂CH₂⁺Cl⁻. The parent amine acts as a nucleophile toward FcCH₂Cl to give 1a–d and as a base toward NMe₂CH₂⁺ to give FcCH₂NMe₂H⁺, NMe₂H and (Me₂N)₂CH₂. The FcCH₂Cl intermediate is intercepted by NEt₃ while KCN or LiH do not successfully compete with FcCH₂NMe₂. A new, non-toxic, selective, high-yield route to 1d is also presented. Electrochemistry and UV–vis spectroelectrochemistry reveal, that the two identical redox centers in 1a–d are essentially non-interacting. Individual E_1/2 values have been determined for different solvents by digital simulation. The corresponding ferrocenium salts were prepared by either chemical or electrochemical means and accordingly characterized. Our studies are augmented by X-ray structure analyses of 1b, 1d and 2d. 1d contains three different cation conformers and four molecules of water per unit cell. The latter are hydrogen bonded to the chloride counterions to form one-dimensional infinite chains parallel to the a axis.     

A complex of buckminsterfullerene with sulfur,C60·2S8: synthesis and crystal structure

The C₆₀·2S₈ complex was prepared by reaction of buckminsterfullerene C₆₀ with sulfur in trichloroethylene and its single-crystal X-ray structure was studied at room temperature. Crystals of this compound are monoclinic, space groupC 2/c, a=20.90(1),b=21.10(1),c=10.537(9) Å, =111.29(7)°,Z=4,d _calc=1.89 g·cm^–3. The crystal structure of the C₆₀·2S₈ complex consists of packed fullerene molecules that form hexagonal channels along thec axis with eight-membered crown-shaped S₈ cyclic molecules inside the channels. The distances between the centers of neighboring fullerene molecules are 10.036(7), 10.636(7), and 10.537(9) Å. Each C₆₀ molecule is linked to eight S₈ molecules with ten shortened intermolecular contacts C...S 3.41(1)–3.52(2) Å. The average values of the C=C and C-C bond lengths are 1.32(3) and 1.47(3) Å, which attest to a significant degree of localization of electron density in the c₆₀ molecule.Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 262–266, February, 1994.     

ESR study of adducts of diisopropylphosphoryl radicals with C60C[P(O)(OEt)2]2 2 isomers

The radical adducts of the P^·(O)(OPrⁱ)₂ (R^·) radicals with C₆₀C[P(O)(OEt)₂]_{2 2} fullerene derivatives were studed by ESR spectroscopy. The number of stable regioisomers of phosphorylfullerenyl radicals formed by addition of the phosphoryl radicals to the C₆₀C[P(O)(OEt)₂]_{2 2} isomers depends on the mutual position of the organophosphorus groups and decreases in the series trans-2 > trans-3 trans-4 > e. The rate constants for addition of the R^· radicals to the trans-3 regioisomer (k = 1.7·10⁸ L mol^–1 s^–1) were determined.     

Selective reduction of fullerene C60 by metals in neutral and alkaline media. Interaction of C60 with KOH

The reduction of fullerene C₆₀ by Zn and Mg in DMF was studied both in the presence and absence of KOH. Fullerene C₆₀ was reduced in these systems to form the C₆₀ ^n– (n = 1, 2, and 3) anions. The anions were detected by optical and ESR spectroscopies. It was found that Mg reduced C₆₀ to the monoanion, Mg/KOH and Zn reduced C₆₀ to the dianion, and Zn/KOH reduced C₆₀ to the trianion. Like KCN, potassium hydroxide adds to fullerene upon interaction with C₆₀ in DMF. The reaction of C₆₀ with KOH in benzonitrile was accompanied by the generation of the fullerene monoanion. A possible mechanism of the formation of fullerene monoanions in the presence of KOH is discussed. The degradation of the C₆₀ ^n– anions in air was studied.     

Addition of carbon-centered radicals to C60. Determination of the rate constants by the spin trap method

The rate constants of addition of the^.CMe₃,^.CH₂Me,^.CH₂(CH₂)₃Me,^.CH₂Ph,^.CH₂CH=CH₂, and^.CH(Me)Et radicals to fullerene C₆₀ were determined by the method of competitive addition of free radicals to spin traps. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp 2369–2372, December, 1999.     

Radical functionalization of [60]fullerene and its derivatives initiated by the C(CF3)2C6H4F radical

It was found that the 2-(p-fluorophenyl)hexafluoroisopropyl radical produced by thermal dissociation of the Polishchuk dimer [C(CF₃)₂C₆H₄F]₂ can withdraw, under mild conditions, the H atom from the methyl group of toluene and mesitylene to form the corresponding radicals, whose addition to [60]fullerene occurs more selectively than in the case of photochemical production of these radicals. Dynamics of the step-by-step multiaddition of the radicals to C₆₀ was studied by ESR. It was found that the addition of benzyl radicals affords adducts containing from 3 to 5 benzyl groups, whereas no spin-adducts with five addends were observed for more bulky 3,5-dimethylphenylmethyl radicals. The interaction of 3,5-dimethylphenylmethyl radicals with the metal complexes (η²-C₆₀[IrH(CO)(PPh₃)₂] and (η²-C₆₀[Pd(PPh₃)₂] was studied for the first time. It was shown that the palladium derivative undergoes only demetallation. In the case of the Ir complex, up to 3 radicals add to the fullerene ligand in the same hemisphere where the transition metal is coordinated. The reaction rates are ∼5 times lower than those for C₆₀. The ability of 2-(p-fluorophenyl)hexafluoroisopropyl radicals to dehydrogenate C₆₀H₃₆ was found. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1119–1123, June, 1999.     

UV–visible spectrum of the phenyl radical and kinetics of its reaction with NO in the gas phase

Pulse radiolysis transient UV–visible absorption spectroscopy was used to study the UV–visible absorption spectrum (225–575 nm) of the phenyl radical, C₆H₅(), and kinetics of its reaction with NO. Phenyl radicals have a strong broad featureless absorption in the region of 225–340 nm. In the presence of NO phenyl radicals are converted into nitrosobenzene. The phenyl radical spectrum was measured relative to that of nitrosobenzene. Based upon σ(C₆H₅NO)_{270 nm}=3.82×10⁻¹⁷ cm² molecule⁻¹ we derive an absorption cross-section for phenyl radicals at 250 nm, σ(C₆H₅())_{250 nm}=(2.75±0.58)×10⁻¹⁷ cm² molecule⁻¹. At 295 K in 200–1000 mbar of Ar diluent k(C₆H₅()+NO)=(2.09±0.15)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹.     

Cyclopalladation of mono-, di- and tribenzylamine by palladium(II) acetate: Influence of bulkiness around the nitrogen atom of benzylamine upon internal metallation

Cyclopalladation of mono-, di- and tribenzylamine has been investigated by reacting the corresponding amines with an equimolar amount of palladium(II) acetate (reaction i), or by heating the corresponding bis-amine complexes [Pd(O₂CMe)₂{(PhCH₂)_nNH_3−n}₂] (n=1, 2) (reaction ii). By the reaction i, all the three amines undergo cyclopalladation. However, in the case of the reaction ii, only the dibenzylamine complex [Pd(O₂CMe)₂{(PhCH₂)₂NH}₂] has been converted into a cyclopalladated complex. The reactivity of the three benzylamines towards cyclopalladation has been discussed in terms of the co-ordinating ability influenced by the bulkiness around the nitrogen atom. Temperature-dependent ¹H-NMR spectra are observed for mononuclear cyclopalladated complexes [Pd(O₂CMe){C₆H₄CH₂N(CH₂Ph)₂–C¹, N}L] (L=PPh₃, AsPh₃) and are attributed to the dissociation of the nitrogen atom in the cyclopalladated chelate ring. A heteroleptic bis-cyclopalladated complex [Pd[C₆H₄CH₂N(CH₂Ph)₂–C¹, N](C₆H₄CH₂NMe₂–C¹, N)] has also been prepared. X-ray crystallographic studies on [{Pd(O₂CMe)[C₆H₄CH₂N(CH₂Ph)₂–C¹, N]}₂] and [Pd[C₆H₄CH₂N(CH₂Ph)₂–C¹, N](C₆H₄CH₂NMe₂–C¹, N)] have been reported.     

Spectral and kinetic characteristics of cycloalkyl radicals in the liquid phase

The C₅–C₁₀ cyclolakyl radicals have a weak light absorption in the 240–300 nm wavelength range that is due to Rydberg transition to the 3s orbital. The extinction coefficients at 250 nm are in the range of 350–900 mol^–1 dm³ cm^–1. At this wavelength for the C₆–C₁₀ radicals a local maximum appears. The radical decay obeys second order kinetics. The kinetic characteristics of the cyclic and linear radicals are generally similar, indicating that the rings are flexible and can easily overcome steric constraints in the termination process. Both the light absorption and decay characteristics of the cyclopentyl radical are somewhat different from those of the other radicals that are attributed to the special co-planar arrangement.     

Relationship between reduction potentials and electron affinities of fullerenes and their derivatives

A linear relationship was found between the first reduction potentials (E°_red) and electron affinities (EA) for fullerenes C₆₀ and C₇₀, their hydro- and fluoro-derivatives, and aromatic hydrocarbons: E°_red = –3.04 + 0.81·EA. This equation was used to estimate the unknown values of EA = 2.45 eV for C₆₀H₂, 2.47 eV for C₇₀H₂, –0.15 eV for C₇₀H_36—38, –0.41 eV for C₇₀H_44—46, and E°_red = –1.74—–1.91 V (vs. Fc^0/+) for C₆₀H₁₈.     

Catalytic polyaddition of benzene to fullerene and properties of the reaction product

The use of a catalyst based on aluminum trichloride and copper dichloride in the reaction of fullerene with benzene afforded C₆₀Ph₁₉H₁₉. At 400°C, this compound eliminates hydrogen to form C₆₀Ph₁₉. The compounds obtained are characterized by their high solubility in organic solvents, film-forming properties, and photoluminescence at 520 nm. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1219–1221, June, 1997.     

Inertness of C<Subscript>60</Subscript> fullerene toward RO<Subscript>2</Subscript><Superscript>·</Superscript> peroxy radicals

The reactivity of fullerene C₆₀ toward peroxy radicals RO₂ ^· was tested by the chemiluminescence method. A comparison of the influence of C₆₀ and known inhibitors on the kinetics of liquid-phase chemiluminescence (CL) during oxidation of a series of hydrocarbons (ethyl-benzene, cyclohexane, n-dodecane, and oleic acid) shows that the fullerene does not react with the RO₂ ^· radicals. A sharp decrease in the CL intensity observed upon C₆₀ addition is caused by the quenching of CL emitters with fullerene but not by inhibition of hydrocarbon oxidation. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1808–1811, August, 2005.     

Electronic spectra and electron structure of fullerene complex (η2-C60)Fe(CO)4

The electronic spectrum of the C₆₀Fe(CO)₄ complex was studied in a toluene solution. The more intense absorption of C₆₀Fe(CO)₄ in the visible region, relative to the free C₆₀, can be attributed to the effect of lower symmetry of the C₆₀ fullerene cage in C₆₀Fe(CO)₄ and, thus, relaxation of selection rules for forbidden internal electronic transitions of C₆₀. No bands of the charge transfer from 3d(Fe) to C₆₀ orbitals were observed in the visible region of the complex spectrum. Assignment of the bands was confirmed by semiempirical calculations of the electronic spectrum.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1453–1458, June, 1996     

Anionic zirconium and hafnium borohydride complexes

Zirconium and hafnium tetrachlorides react with NaBH₄, in dimethoxyethane (DME) to give [Na(DME)₃][M(BH₄)₅]. These compounds react with Bu₄NBH₄ and Ph₄PBH₄ to give (R₄E)[M(BH₄)₅]. Bidentate and tridentate BH ₄ ^– occur in [M(BH₄)₅]^– according to IR spectroscopy. Data from¹H and¹H-{¹¹B} NMR spectra are consistent with intermolecular exchange of BH₄ ligands in solutions of complexes (I)–(VI). The BH₄groups and the bridging and terminal protons in each BH₄ group equilibrate rapidly. Heating the complexes (I)–(VI) reduces the central atom, releases diborane, and decomposes the outer-sphere cation. The neutral borohydrides M(BH₄)₄, can be prepared by thermolysis of the sodium salts (I) and (II).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1207–1214, June, 1990.     

Synthesis of a Fullerene Derivative of Benzo[18]crown-6 by Diels-Alder Reaction: Complexation Ability,Amphiphilic Properties,and X-Ray Crystal Structure of a Dimethoxy-1,9-(methano[1,2]benzenomethano)fullerene[60] Benzene Clathrate

A fullerene derivative 1 of benzo[18]crown-6 was obtained by Diels-Alder addition of fullerene[60](C₆₀) to the ortho-quinodimethane prepared in situ from 4,5-bis(bromomethyl)benzo[18]crown-6 ( 3 ) with Bu₄NI in toluene. Extraction experiments show that the complexation of K⁺ ions strongly increases the solubility of 1 in protic solvents like MeOH. Using Langmuir-Blodgett techniques, monolayers of the highly amphiphilic fullerene-derived crown ether 1 and its K⁺ ion complex were prepared. An X-ray crystal structure was obtained from a benzene clathrate of comparison compound 2 , synthesized by Diels-Alder reaction of C₆₀ with the ortho-quinodimethane derived from 1,2-bis(bromomethyl)-4,5-dimethoxybenzene ( 4 ). Both the fullerene molecule 2 and the benzene molecule are fully ordered in a crystal packing which is stabilized by intermolecular van-der-Waals contacts between the benzene ring and the C-spheres, intermolecular C…?C contacts between the C₆₀ moieties, and intermolecular O…?C contacts between the O-atoms of the veratrole moieties and fullerene C-atoms.     

Study of equilibria in solutions of buckminsterfullerene exohedral derivative, (η2-C60)Pd(PPh3)2, using electrochemical methods and electronic spectroscopy

Polarization curves of electrochemical oxidation and reduction, as well as electronic absorption spectra of the palladium complex of fullerene, C₆₀Pd(PPh₃)₂, and its mixtures with Pd(PPh₃)₄ have been studied in toluene-acetonitrile (9:1) solutions. The experimental data can be explained by the assumption that equilibrium takes place between the initial complex, polymetallated compounds, C₆₀[Pd(PPh₃)₂]_n (n=1–4), and free fullerene, C₆₀.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2153–2158, December, 1994.This work was supported by the Russian Foundation for Basic Research, Project No. 93-03-18725.     

Kinetic and ESR studies on radical polymerization of methyl methacrylate in the presence of fullerene

The effect of fullerene (C₆₀) on the radical polymerization of methyl methacrylate (MMA) in benzene was studied kinetically and by means of ESR, where dimethyl 2,2′-azobis(isobutyrate) (MAIB) was used as initiator. The polymerization rate (R_p) and the molecular weight of resulting poly(MMA) decreased with increasing C₆₀ concentration ((0–2.11) × 10⁻⁴ mol/L). The molecular weight of polymer tended to increase with time at higher C₆₀ concentrations. R_p at 50°C in the presence of C₆₀ (7.0 × 10⁻⁵ mol/L) was expressed by R_p = k[MAIB]^0.5[MMA]^1.25. The overall activation energy of polymerization at 7.0 × 10⁻⁵ mol/L of C₆₀ concentration was calculated to be 23.2 kcal/mol. Persistent fullerene radicals were observed by ESR in the polymerization system. The concentration of fullerene radicals was found to increase linearly with time and then be saturated. The rate of fullerene radical formation increased with MAIB concentration. Thermal polymerization of styrene (St) in the presence of resulting poly(MMA) seemed to yield a starlike copolymer carrying poly(MMA) and poly(St) arms. The results (r₁ = 0.53, r₂ = 0.56) of copolymerization of MMA and St with MAIB at 60°C in the presence of C₆₀ (7.15 × 10⁻⁵ mol/L) were similar to those (r₁ = 0.46, r₂ = 0.52) in the absence of C₆₀. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2905–2912, 1998