(Indol-3-yl)(DMIX)Iodonium Salts: Novel Electrophilic Indole Reagents.

A new umpolung approach to the C3-H functionalization of indoles with diverse nucleophiles based on the intermediate formation of I(III) reagents is described. The 3,5-dimethylisoxazol-4-yl auxiliary allows for selective indole transfer under catalyst-free conditions, which was impossible using previously reported reagents. Combining the mildness of transition-metal-free conditions and the high reactivity of hypervalent iodine reagents, this protocol tolerates various functional groups and provides access to indoles that are difficult to prepare conventionally.

Oxidative cage opening in the C70 fullerene facilitated by preceding trifluoromethylation.

Two novel derivatives of the C70 fullerene with 9- and 10-membered cage openings were obtained by means of oxidation and decarbonylation of C70(CF3)8. The major product, C70(O)(CF3)8O2, features a cleaved C-C bond transformed into two carbonyl functions plus an ether bridge. The second product, C69O(CF3)8O, has one of the carbonyls replaced with another ether bridge. We provide a DFT analysis of the possible formation pathways to give the oxidized compounds under the action of pyridine N-oxide.

Reversibly switchable methanofullerene by photoexcitation and reduction.

A cyclopropanated derivative of the trifluoromethylated fullerene Cs-C70(CF3)8 demonstrates reversible switching behavior triggered by excited state electron transfer or by negative charging. The switching between the state with connected 62-electron π-system and the state with disjoint 28- and 32-electron conjugated caps is effected by opening/closure of the cyclopropanated bond. A pronounced alteration of the electronic properties upon seemingly minor changes in a large fullerene molecule is an attractive feature for the organic electronic devices where similar fullerene compounds are commonly utilized as electron acceptor materials.

Difluoromethylenation of fullerene C70 provides isomeric diversity and availability of equatorial [5,6]-homofullerene C70(CF2).

We report synthesis, isolation, and spectroscopic characterization of the novel [5,6]-open C70(CF2) isomer III along with the already known [6,6]-closed and [6,6]-open C70(CF2) isomers I and II. The compounds were obtained in a ratio of I : II : III = 4 : 6 : 1 by means of thermal treatment of C70 fullerene with sodium chlorodifluoroacetate. This product composition is explained with the use of quantum chemical calculations that identify the reaction pathway as a two-stage nucleophilic cyclopropanation rather than the previously postulated carbene addition. We further report the first cyclic voltametric studies for the whole set of isomers of C70(CF2). Together with the DFT data, they demonstrate that the LUMO is stabilized in both isomer II ([6,6]-open) and III ([5,6]-open) by 0.1 eV with respect to the pristine C70, and isomer III has the lowest reorganization energy of all.

Dissociative Electron Attachment to Hexachlorobenzene.

Gas phase molecules of hexachlorobenzene (C6 Cl6 ) were investigated by means of dissociative electron attachment spectroscopy (DEAS). Three channels of molecular negative ions decay have been identified: abstraction of Cl- and Cl2- as well as electron detachment (τa ∼250 µs at 343 K). All three channels exhibit temperature dependence. The adiabatic electron affinity estimated using a simple but typically accurate Arrhenius model (EAa =1.6-1.9 eV) turns out to be much higher than the quantum-chemical predictions (EAa =0.9-1.0 eV). We discuss the possible reasons behind the observed discrepancy.

Electrochemically Induced Dimerization of p9mp-C70(CF3)12 Trifluoromethylated Fullerene.

We report a comprehensive study of a novel isomer of C70(CF3)12, p9mp-C70(CF3)12, whose electrochemical behavior differs from most of the other trifluoromethylated fullerenes. The addition pattern of p9mp-C70(CF3)12 is established by means of 19F-19F COSY NMR spectroscopy and DFT calculations. Like p7mp-C70(CF3)10, the new isomer p9mp-C70(CF3)12 undergoes dimerization to the [C70(CF3)12]22- upon single-electron reduction. The electrochemical observations are supported by the DFT calculations of dimerization energy and the temperature dependence of the CW X-band EPR spectroscopy data. Experimentally determined dimerization energies of p9mp-C70(CF3)12-• and p7mp-C70(CF3)10-• in solution are ca -8 and -26 kJ mol-1, respectively, in good correspondence with DFT data.

Water-Promoted Reaction of C60Ar5Cl Compounds with Thiophenes Delivers a Family of Multifunctional Fullerene Derivatives with Selective Antiviral Properties.

Here we report a reaction of the fullerene derivatives C60Ar5Cl, which enables the substitution of Cl with thiophene residues and the formation of the novel family of C1-symmetrical C60 fullerene derivatives with six functional addends C60Ar5Th. The discovered reaction provided a straightforward approach to the synthesis of previously inaccessible multifunctional water-soluble fullerene derivatives, including the compounds with antiviral activity against human immunodeficiency and influenza viruses.

Green and rapid preparation of long-term stable aqueous dispersions of fullerenes and endohedral fullerenes: The pros and cons of an ultrasonic probe.

A green, scalable, and sustainable approach to prepare aqueous fullerene dispersions (AFD) C60, C70, endohedral metallofullerene Gd@C82, and their derivatives C60Cl6, C70Cl10, and supramolecular and ester-like derivatives, 10 fullerene species total, is proposed. For the first time, an immersed ultrasonic probe was used to preparing dispersions for pristine fullerenes without addends. Both ultrasound-assisted solvent-exchange and direct sonication techniques for AFD preparation using an immersed probe were tested. The average time for AFD preparation decreases 10-15 times compared to an ultrasound-bath-assisted technique, while final fullerene concentrations in AFDs remained at tens of ppm (up to 80 ppm). The aqueous dispersions showed long-term stability, a negatively charged surface with a zeta potential up to -32 mV with an average nanocluster diameter of no more than 180 nm. The total anionic and cationic compositions of samples were found by inductively coupled plasma atomic emission spectroscopy and chromatographic techniques. The highlights and challenges of using an ultrasound probe for AFD production are discussed.

Dissociative Electron Attachment to 2,3,6,7,10,11-Hexabromotriphenylene.

2,3,6,7,10,11-Hexabromotriphenylene (HBTP) and 2,3,6,7,10-pentabromotriphenylene (PBTP) were investigated by means of dissociative electron attachment spectroscopy (DEAS). The dominant decay channel of the transient molecular negative ions consists of elimination of Br- with resonances in the low electron energy region. Formation of long-lived parent anions with autodetachment lifetime τa = 310 µs is observed at thermal electron energies. The adiabatic electron affinities, EAa = 1.12 ± 0.1 eV in HBTP and 1.09 ± 0.1 eV in PBTP, evaluated using a simple Arrhenius approach are in good agreement with those predicted by DFT (XYG3/Def2-TZVPP//PBE0/Def2-TZVPP) calculations.

Facile Separation, Spectroscopic Identification, and Electrochemical Properties of Higher Trifluoromethylated Derivatives of [70]Fullerene.

We survey the structure and electronic properties of the family of higher trifluoromethylated C70 (CF3 )n molecules with n=14, 16, 18, and 20. Twenty-two available compounds, of which thirteen are newly obtained and characterized, demonstrate the broad diversity of π-system topologies, which enabled us to study the interplay between the CF3 addition pattern and the electronic properties. UV/Vis spectroscopic and cyclic voltammetric studies demonstrate the importance of the exact addition pattern rather than the plain number of addends. Of particular interest is the skew pentagonal pyramid (SPP) addition pattern, which enables formation of closed-shell cyclopentadienyl anions C70 (CF3 )n-1- through CF3 detachment upon electron transfer. A detailed study of the process is presented for a SPP-C70 (CF3 )16 where potentiostatic electrolysis at the second reduction potential gives C70 (CF3 )15- oxidizable to a persistent C70 (CF3 )15. radical. Together with the literature data for the lower C70 (CF3 )n compounds with n=2-12, the present results show good correlation between the experimental boundary level positions and the DFT predictions. The compounds turn out to be electron acceptor molecular semiconductors with experimental LUMO energies and HOMO-LUMO gaps within the ranges of -4.3 to -3.7 eV and 1.6 to 3.3 eV, respectively, depending on the shape of the conjugated fragments. The HOMO levels fall within the range of -5.6 to -6.9 eV and show linear correlation with the number of addends.

Tightly Bound Double-Caged [60]Fullerene Derivatives with Enhanced Solubility: Structural Features and Application in Solar Cells.

A series of novel highly soluble double-caged [60]fullerene derivatives were prepared by means of lithium-salt-assisted [2+3] cycloaddition. The bispheric molecules feature rigid linking of the fullerene spheres through a four-membered cycle and a pyrrolizidine bridge with an ester function CO2 R (R=n-decyl, n-octadecyl, benzyl, and n-butyl; compounds 1 a-d, respectively), as demonstrated by NMR spectroscopy and X-ray diffraction. Cyclic voltammetry studies revealed three closely overlapping pairs of reversible peaks owing to consecutive one-electron reductions of fullerene cages, as well as an irreversible oxidation peak attributed to abstraction of an electron from the nitrogen lone-electron pair. Owing to charge delocalization over both carbon cages, compounds 1 a-d are characterized by upshifted energies of frontier molecular orbitals, a narrowed bandgap, and reduced electron-transfer reorganization energy relative to pristine C60 . Neat thin films of the n-decyl compound 1 a demonstrated electron mobility of (1.3±0.4)×10-3  cm2 V-1 s-1 , which was comparable to phenyl-C61 -butyric acid methyl ester (PCBM) and thus potentially advantageous for organic solar cells (OSC). Application of 1 in OSC allowed a twofold increase in the power conversion efficiencies of as-cast poly(3-hexylthiophene-2,5-diyl) (P3HT)/1 devices relative to the as-cast P3HT/PCBM ones. This is attributed to the good solubility of 1 and their enhanced charge-transport properties - both intramolecular, owing to tightly linked fullerene cages, and intermolecular, owing to the large number of close contacts between the neighboring double-caged molecules. Test P3HT/1 OSCs demonstrated power-conversion efficiencies up to 2.6 % (1 a). Surprisingly low optimal content of double-caged fullerene acceptor 1 in the photoactive layer (≈30 wt %) favored better light harvesting and carrier transport owing to the greater content of P3HT and its higher degree of crystallinity.

Reductive Hydrogenation of Cs -C70 (CF3 )8 and C1 -C70 (CF3 )10.

CF3 -derivatized fullerenes prove once again to be promising scaffolds for regioselective fullerene functionalization: now with the smallest possible addends-hydrogen atoms. Hydrogenation of Cs -C70 (CF3 )8 and C1 -C70 (CF3 )10 by means of reduction with Zn/Cu couple in the presence of water proceeds regioselectively, yielding only one major isomer of C70 (CF3 )8 H2 and only two for C70 (CF3 )10 H2 , whose addition patterns are combined in the only abundant isomer of C70 (CF3 )10 H4 . The observed selectivity is governed by the electronic structure of trifluoromethylated substrates. Interestingly, we discovered that Clar's theory can be utilized to predict the regiochemistry of functionalization, and we look forward to testing it on forthcoming cases of derivatization of pre-functionalized fullerene building blocks.

Orienting Effect of the Cage Addends: The Case of Nucleophilic Cyclopropanation of C2 -C70 (CF3 )8.

C2 -C70 (CF3 )8 was found to be a very promising substrate in the Bingel and the Bingel-Hirsch reactions combining perfect regioselectivity with much higher reactivity compared to its analogs. The reactions with diethyl malonate yield a single isomer of the monoadduct C70 (CF3 )8 [C(CO2 Et)2 ] and a single C2 -symmetrical bisadduct C70 (CF3 )8 [C(CO2 Et)2 ]2 . The Bingel-Hirsch variation is particularly interesting in that it additionally affords, in a similar regioselective manner, the unexpected alkylated derivatives C70 (CF3 )8 [CH(CO2 Et)2 ]H and C70 (CF3 )8 [C(CO2 Et)2 ][CH(CO2 Et)2 ]H. The novel compounds have been isolated and structurally characterized by means of (1) H and (19) F NMR spectroscopy as well as single-crystal X-ray diffraction. The mechanistic and regiochemical aspects of the reaction are explained with the aid of DFT calculations.

Transalkylation of higher trifluoromethylated fullerenes with C70: a pathway to new addition patterns of C70(CF3)8.

We report three new isomers of C70(CF3)8, structurally related to p(7)mp-C70(CF3)10, that are inaccessible by direct trifluoromethylation, but can be easily identified among the products of the transalkylation of higher trifluoromethylfullerenes with C70. The reported compounds are characterized by UV/Vis, 1 D and 2 D COSY (19)F NMR spectroscopy, and DFT calculations. A rather unusual addition pattern is observed in p(6),i-C70(CF3)8 in which one addend is attached remotely from the others; polarization of the adjacent unsaturated bonds by the addend makes the molecule readily oxidizable.

Alkali-metal trichloroacetates for dichloromethylenation of fullerenes: nucleophilic addition-substitution route.

The first experimental evidence that fullerenes react with alkali-metal trichloroacetates through a nucleophilic addition-substitution route, yielding dichloromethylenefullerenes as the final products, is reported. The intermediates, C60 (CCl3 )(-) and C70 (CCl3 )(-) anions, have been isolated in their protonated forms as ortho-C60 (CCl3 )H, as well as three ortho and one para isomer of C70 (CCl3 )H. The structures were unambiguously determined by means of (1) H, (13) C, and (1) H-(13) C HMBC NMR spectroscopy along with UV/Vis spectroscopy. The observed regiochemistry was analyzed with the aid of quantum chemical calculations. Conversion of the protonated compounds into the [6,6]-closed C60/70 (CCl2 ) cycloadducts under basic conditions can be effected only for the ortho isomers, whereas para-C70 (CCl3 )H decomposes back into pristine C70 .

[6,6]-Open and [6,6]-closed isomers of C70(CF2): synthesis, electrochemical and quantum chemical investigation.

Novel difluoromethylenated [70]fullerene derivatives, C70(CF2 )n (n=1-3), were obtained by the reaction of C70 with sodium difluorochloroacetate. Two major products, isomeric C70(CF2 ) mono-adducts with [6,6]-open and [6,6]-closed configurations, were isolated and their homofullerene and methanofullerene structures were reliably determined by a variety of methods that included X-ray analysis and high-level spectroscopic techniques. The [6,6]-open isomer of C70(CF2 ) constitutes the first homofullerene example of a non-hetero [70]fullerene derivative in which functionalisation involves the most reactive bond in the polar region of the cage. Voltammetric estimation of the electron affinity of the C70(CF2 ) isomers showed that it is substantially higher for the [6,6]-open isomer (the 70-electron π-conjugated system is retained) than the [6,6]-closed form, the latter being similar to the electron affinity of pristine C70. In situ ESR spectroelectrochemical investigation of the C70(CF2 ) radical anions and DFT calculations of the hyperfine coupling constants provide evidence for the first example of an inter-conversion between the [6,6]-closed and [6,6]-open forms of a cage-modified fullerene driven by an electrochemical one-electron transfer. Thus, [6,6]-closed C70(CF2 ) constitutes an interesting example of a redox-switchable fullerene derivative.