Regiochemistry of Azide Additions to [70]Fullerene

Abstract

In this paper we report for the first time on the reaction of C₇₀ with alkyl azides and show that the [3+2]-cycloaddition occurs preferably at bond 7 followed by bond 5 to give two regioisomeric A/B-triazolines and one C/C-triazoline Thermal extrusion of N₂ from these triazolines leads to open [5,6]-bridged iminofullerenes as A/A- and B/C-isomers as well as to the ring closed [6,6]-bridged analogues as A/B- and C/C-isomers. These results are in line with the corresponding thermal reaction of C₇₀ with diazomethane.     

Pyrolytic Trifluoromethylation of [76]-, [78]-, [84]-, and Aza[60]Fullerenes with Silver Trifluoroacetate; Evidence for Coordination of Fullerenes to Silver

Pyrolytic trifluoromethylation of [76], [78], [84], and aza[60]fullerenes with silver trifluoroacetate at 300°C results in extensive polyaddition of up to 18, 18, 20 and 20 CF₃ groups, respectively. In contrast to trifluoromethylation of [60]- and [70]fullerenes that give a full range of derivatives ranging upwards from C_n(CF₃)₂, [76]-, [78]-, and [84]-fullerenes only give C_n(CF₃)_6-18 derivatives, largely in the 10-12 CF₃ range; reaction with [76]fullerene is accompanied by formation of C₆₀(CF₃)₆ attributed to cage fragmentation. For aza[60]fullerene the hexa-addition level dominates, in contrast to its other reactions which give predominantly penta-addition products. All the compounds showed peaks at 1256±2 and 1180-1190 cm^-1, due to the CF₃ group, and peaks in this region are shown also by the soluble extract obtained on trifluoromethylation of nanotubes. As in trifluoromethylation of [60]- and [70]-fullerenes, the products obtained initially are involatile, attributed to formation os silver complexes; these are decomposed on subsequent solution in toluene. Mixed isomeric trifluoromethylated C₆₀F₈ derivatives viz. C₆₀F₇CF₃, C₆₀F₆(FG₃)₂, C₆₀F₅(CF₃)₃ and C₆₀F₄(CF₃)₄, and C₆₀F₄CF₃CF₂CF₃ (a C₆₀F₆ derivative) have been isolated from fluorination of [60]fullerene with MnF₃/K₂NilF₆ at 510°C.     

HPLC Diode-Array Analysis of C60 and C70 Polymeric Fullerene Oxides (Fullerene Polymeric Ozonides)

It is shown by HPLC diode-array analysis that the C₆₀ and C₇₀ polymeric fullerene oxides ([C₆₀]-PFOs and [C₇₀]-PFOs) which are polymeric ozonides, are composed by nine different components. The ozonide derivatives of C₆₀ and C₇₀ have been proved to be practically analogous in chemical structure and composition. The most important component of both [C₆₀]-PFOs and [C₇₀]-PFOs accounts for about 3/4 of each sample. The overozonation of [C₆₀]-PFOs in methanol has been studied and shown to not produce any significant changes.     

Spectroscopic Evidence for Anionic Coordination Complexes of the Transition Metals with C70 and the Higher Fullerenes C76, C78, C82, C84, C86, C90, and C92

The carbonylate anions [M(CO)₅]^- (M = Mn, Re), [Co(CO)₄]^-, [CpFe(CO)₂]^-, and [CpM(CO)₃]^- (M = Mo, W) react with C₇₀ via single electron transfer processes to give, respectively, the corresponding 17-electron, metal-centered radicals Co(CO)₄, M(CO)₅ (M = Mn, Re), CpFe(CO)₂, and CpM(CO)₃ (M = Mo, W) in addition to the radical anion C₇₀^-. In secondary thermal or photochemical processes, the metal-centered radicals Co(CO)₄ and M(CO)₅ (M = Mn, Re) combine with the C₇₀^- to form the new η²-C₇₀ complexes [Co(CO)₃(η²-C₇₀)]^- and [M(CO)₄(η²-C₇₀)]^-. However, the metal-centered radicals CpM(CO)₃ (M = Mo, W) require photolysis to react with C₇₀^- to form [CpM(CO)₂(η²-C₇₀)]^-, whereas neither thermolysis nor photolysis induces reaction between CpFe(CO)₂ and C₇₀^-. The photochemical reaction of [Mn(CO)₅]^- with a mixture of higher fullerenes known to contain at least C₇₆, C₇₈, C₈₄, C₈₆, and C₉₀ resulted similarly in the formation of the higher fullerene complexes [Mn(CO)₄(η²-C_n)]^- (n = 76, 78, 80, 82, 84, 86, 88, 90, 92, 96, and 98), all identified using electrospray mass spectrometry.     

UNSTABLE PRODUCTS FROM THE OZONATION OF C60 IN SOLVENTS

The ozonation of a solution of C₆₀ in toluene results in the formation of several unstable compounds C₆₀X and C₆₀Y[1-5] which decay completely at room temperature within about 1 h. The products are oxides C₆₀O[6,6], C₆₀O₂[I], C₆₀O₂[II], and possibly an isomer of C₆₀O₃. The transformations are not due to oxidation by atmospheric oxygen but are spontaneous. The ozonation of a solution of C₆₀O[6,6] in toluene results in the formation of two unstable compounds C₆₀Z[1-2] which also decay completely to C₆₀O₂[I] and C₆₀O₂[II]. It is suggested that all unstable “parents” are ozonides.     

Loss of Chlorine from C60 and C70 Chlorides

Fullerene contents of chlorinated C₆₀ and C₇₀ were determined with HPLC. n-Values of C₆₀Cl_n and C₇₀Cl_n were determined from mass increase during synthesis, MALDI-TOF mass spectrometry, PIXE, Nuclear Microprobe (¹²C[d,p]¹³C), and Electron Microprobe analysis. n-Values obtained immediately after synthesis were in the range 31-45. Best values obtained later were in the range 10-20. It is suggested that (i) the samples lost CS₂ or CS₂/CCl₄, or Cl of “crystallization” after synthesis, (ii) after synthesis the samples lost Cl bound to C₆₀ (iii) Cl was lost during the analysis, or (iv) some of all three.     

THE ELUSIVE C60S: THREE ATTEMPTED SYNTHESES

Results of semiempirical energy calculations suggested that a [6,6]-closed C₆₀S fullerene sulfide might be stable. Attempts were therefore undertaken to synthesize the compound by UV photolysis of C₆₀ in CS₂ and by the heating of mixtures of C₆₀ and S₈ to 325 and 400°C. Any sulfide, if formed, was present in undetectably small quantities. However, [¹²C₆₀³⁴S]^- ions were observed when a mixture of solid C₆₀ and elemental sulfur was analyzed by Laser Desorption Ionization Time-of-Flight mass spectrometry.     

Trifluoromethylation of [60]- and [70]Fullerene in the Ionization Chamber of a Mass Spectrometer

Both [60]- and [70]fullerene react with either the Scherer radical (perfluorodiisopropylethylmethyl, C₉F₁₉), a mixture of branched perfluorononenes (C₉F₁₈, the product of hexafluoropropene trimerization), or β-fluorosulphatotetrafluoroethyldiheptafluoroisopropylmethyl radical (C₉F₁₈OSO₂F) in the ionization chamber of a mass spectrometer to give the positive parent ions of trifluoromethylation products, the reaction being accompanied by hydrogen addition. The reaction occurs at least partly on the walls of the ionization chamber, by a radical mechanism employing CF₃ radicals formed from the radical reactants both thermally and under electron impact; only the latter route occurs with the perfluorononenes.     

Preparation and characterization of C60S16 and C70S48 thin films

In this study, we have investigated different methods for preparation of thin films of C₆₀ and C₇₀-sulfur compounds. Films of good quality were obtained by reaction of amorphous C₆₀ and C₇₀ films with a saturated sulfur solution in toluene at 40°C or with saturated sulfur vapour at a temperature of 140°C for several hours. The quality of the fullerene-sulfur films were strongly dependent on the microstructure of the initially deposited fullerene film and the synthesis temperature. X-ray diffraction analyses showed that both methods lead to the formation of films consisting of C₆₀S₁₆ and C₇₀S₄₈ (space groups C 2/c and Amm2, respectively). C₆₀S₁₆ films synthesised on Al₂O₃(012) and Si(100) substrates were texture-free while C₇₀S₄₈ films typically exhibited a preferential (100) orientation. The films were also characterised by Raman and IR- spectroscopy, which confirmed that the interactions between the fullerene molecules and the S₈ rings are weak. The fullerene-sulfur compounds were found to be unstable at high vacuum conditions. Both materials C₆₀S₁₆ and C₇₀S₄₈ are non-conductive at room temperature with conductivities less then 10⁻⁵ (Ω/cm).     

Synthesis and Spectral Characterization of Difunctional Fullerenes

The oxidation of C₆₀ with m-chloroperbenzoic acid gave C₆₀O₂ with a high positional selectivity, as the ¹³C NMR analysis suggested. Diadducts C₆₀CCI₂O, C₆₀CCl₂(anthracene), C₆₀CCl₂[(CH₂CH₂)₂N₂], and C₆₀CCI₂[Pt-(PPh₃)₂] were synthesized, isolated, and characterized by negative ion FAB mass spectroscopy.     

ISOLATION AND CHARACTERISATION OF C60(CF3)2

From the products of reactions of [60]fullerene with either K₂PtF₆ at 470 °C or AgF at 520 °C, we have isolated C₆₀(CF₃)₂, the simplest trifluoromethylfullerene, which gives a single ¹⁹F NMR line at -69.5 ppm. The HPLC retention time is less than that of C₆₀F₂ confirming the trend observed for other fluoro- vs. trifluoromethylfullerenes namely that the latter elute more rapidly. Other trifluoromethyl- containing species, C₆₀(CF₃)₄O, C₆₀F₅CF₃, C₆₀(CF₃)₄H₂, C₆₀(CF₃)₆H₂, and C₆₀(CF₃H)₃ were detected in the product mixture.     

Synthesis of fullerenes from carbon powder by using high power induction thermal plasma

Radio frequency (rf) inductively coupled thermal plasma (ICTP) was used to fabricate fullerenes (C₆₀,C₇₀, etc.) by direct evaporation of carbon powder injected into the plasma. Spectroscopic observation of the plasma was made for molecular band spectra of C₂ and atomic lines of C. The formation of fullerenes C₆₀ and C₇₀ as well as higher fullerenes were checked and recognized by high performance liquid chromatography (HPLC) and time-of-flight mass spectrometer (TFMS). The suitable conditions for the synthesis of fullerenes within the experimental conditions adopted were 10-kPa plasma pressure, with a considerably higher flow rate of approximately 150 l/min for mixed-gas condition of Ar, He and CO₂, with carbon powder of average diameter 20 μm. The results showed that the productivity of fullerenes has a relation to the intensity of C₂ molecular and C atomic spectra from the induction plasma. Mixing of Si with C particles has a kind of role in enhancing the synthesis rate of fullerenes C₆₀, as well as the higher order fullerenes.     

Some New Aspects of Chlorination of Fullerenes

The effect of the reagent ratio, reaction time and power of the reagent on the product composition in chlorination of [60]fullerene was studied. Chlorofullerenes C₆₀Cl₆, C₆₀Cl₈, C₆₀Cl₁₀, C₆₀Cl₁₂, C₆₀Cl₁₄, and C₆₀Cl₂₆ were synthesized and characterized by chemical analysis, FTIR, ¹³C NMR, and MALDI TOF mass spectrometry. The experimental data supported the coexistence of several isomers of C₆₀Cl_n (n = 8, 10, 12, 14, 26); the mixtures were not separated so far. Semiempirical calculations (AM1, PM3) were used to analyze the addition patterns and resulted in the most favorable structures of C₆₀Cl_8-26. Chlorination of C₇₀ under various conditions invariably yielded C₇₀Cl₁₀.     

Solubility of Fullerene C60 and C70 in Toluene, o-Xylene and Carbon Disulfide at Various Temperatures

The solubilities of fullerene C₆₀ and C₇₀ in toluene, o-xylene and carbon disulfide between the melting point and boiling point of the solvents, respectively, have been measured. The temperature dependent solubility of C₆₀ displays anomalous behaviors. A solubility maximum of C₆₀ around 0 °C for toluene and carbon sulfide and around 30 °C for o-xylene was observed. The temperature-dependent solubility of C₇₀ behaves normally for all the three solvents studied.     

GROUP TRANSFER AND DIMERIZATION PROCESSES OF C60(CN)2 UNDER ATMOSPHERIC PRESSURE IONIZATION CONDITIONS

Neutral and anionic C₆₀(CN)₂ were investigated with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) mass spectrometry. It was observed that its anions underwent cyano- group and oxygen transfer, and dimerization processes in ESI conditions to form C₆₀(CN)₃H^-, C₆₀(CN)₂(OH₂)^-, [C₆₀(CN)₃H]^-₂, [C₆₀(CN)₂(OH₂)]^-₂ and [(C₆₀)₂(CN)₂(OH)]^-. Meanwhile, neutral C₆₀(CN)₂, for which no signal was observed in ESIMS, showed a base peak corresponding to C₆₀(CN)₂Cl^- in APCIMS spectra with CHCl₃ used as solvent, while only a molecular ion peak corresponding to C₆₀(CN)^-₂ was observed for the toluene solution of neutral C₆₀(CN)₂ in the same conditions. Possible mechanisms for group transfer and dimerization were proposed based on these observations.     

Direct and Catalytic Hydrogenation of Buckminsterfullerene C60

C₆₀H₁₈ was obtained by direct hydrogenation of C₆₀ at 400 C and 80 atm C₆₀ was hydrogenated to C₆₀H₃₆ as a main product in the presence of Pd/C catalyst at 180C and 30-70 atm. C₆₀H₃₆ is unstable in dichloromethane and some other organic solvents.     

Synthesis and Characterization of Dialkyl-C61

Three-step synthesis from dialkyl ketone (R₂C=O) with C₆₀ gave C₆₀(CR₂)_n [R = Me, Et, Pr, Bu, (CH₂)₅.; n = 1, 2]. The adducts were isolated by means of gel permeation chromatography, and the monoadducts were characterized by ¹H and/or ¹³C NMR spectroscopies as a mixture of major [5, 6] and minor [6, 6] isomers. Their solubility and electrochemical properties were reported.     

Synthesis of Radiolabeled Fullerenes C60 and C70

The synthesis of radiolabeled C₆₀/C₇₀ for potential biochemical tracer studies was carried out. Vaporization under plasma are conditions (~3000C) of graphite rods impregnated with the ¹⁴C labeled steroid progesterone generates the expected C₆₀/C₇₀ mixture. Isolation and characterization of the ¹⁴C-C₆₀ is reported. Interestingly, the C₇₀ had more radioactivity than the C₆₀.     

The Solid-State Mechanochemical Reaction of Fullerene C60

The solid-state mechanochemical reaction of fullerene C₆₀ by the use of a high-speed vibration milling technique has been applied to the nucleophilic addition of an organozinc reagent to C₆₀, [4+2] cycloaddition of C₆₀ with condensed aromatic hydrocarbons, 1,3-dipolar addition of C₆₀ with organic azides, and dimerization of C₆₀.     

INCORPORATED C70 IN SOL AND GEL

C₇₀ is incorporated in gel by a sol-gel process with using 3-amino-propyltriethoxysilane (NH₂(CH₂)₃Si(OC₂H₅)₃, APTS) and 3-glycidoxypropltrimethoxysilane (CH₂OCHCH₂O(CH₂)₃Si(OCH₃)₃, GPTMS) as precursors. C₇₀ is firstly mixed with APTS to form C₇₀-NH₂(CH₂)₃Si(OC₂H₅)₃ compound by the reaction between C₇₀ and amino-group of APTS, and then the compound is hybridized with GPTMS to form solid gel. The linkage of C₇₀ and APTS is estimated and confirmed with FT-IR spectra, and the UV/Visible spectra of the sol and gel are measured.