Maira R. Cerón

An efficient method to separate Sc3N@C80 Ih and D5h isomers and Sc3N@C78 by selective oxidation with acetylferrocenium [Fe(COCH3C5H4)Cp]+.

Based on the different oxidation potentials of endohedral fullerenes Sc3N@C80 Ih and D5h and Sc3N@C78, an efficient and useful method that avoids HPLC has been developed for their separation. Selective chemical oxidation of the Sc3N@D5h-C80 isomer and Sc3N@C78 by using an acetylferrocenium salt [Fe(COCH3C5H4)Cp](+) followed by column chromatographic separation and reduction with CH3SNa resulted in the isolation of pure Sc3N@Ih-C80, Sc3N@C78, and a mixture of Sc3N@D5h-C80 and Sc3N@C68.

Unexpected Isomerism in cis‐2 Bis(pyrrolidino)[60]Fullerene Diastereomers

Similar yet different: A one-step regio- and diastereoselective synthesis of three new bis(pyrrolidine)[60]fullerenes, one cis-1 and two unprecedented cis-2 diastereoisomers, is reported. The compounds are easily purified using simple chromatographic techniques, and were fully characterized by spectroscopic techniques and X-ray crystallography. A mechanism for the isomeric conversion observed is proposed.

Bis-1,3-dipolar Cycloadditions on Endohedral Fullerenes M3N@Ih-C80 (M = Sc, Lu): Remarkable Endohedral-Cluster Regiochemical Control.

In this work, we briefly report some attempts to control regioisomeric bisadditions on Sc3N@Ih-C80 and Lu3N@Ih-C80 using the tether-controlled multifunctionalization method. We then describe the use of independent (nontethered) bis-1,3-dipolar cycloaddition reactions and the characterization of 5 new bisadducts, 3 for Sc3N@C80 and 2 for Lu3N@C80, which have never been reported before. Unexpectedly and remarkably, 4 of these compounds exhibit relatively high symmetry and 2 of these bisadducts are the first examples of intrinsically chiral endohedral compounds, due to the addition pattern, not to the presence of chiral centers on the addends. Since an analysis of the statistically possible number of bisadduct isomers on an Ih-C80 cage has not been reported, we present it here.

The Regioselectivity of Bingel–Hirsch Cycloadditions on Isolated Pentagon Rule Endohedral Metallofullerenes

In this work, the Bingel-Hirsch addition of diethylbromomalonate to all non-equivalent bonds of Sc3N@D3h -C78 was studied using density functional theory calculations. The regioselectivities observed computationally allowed the proposal of a set of rules, the predictive aromaticity criteria (PAC), to identify the most reactive bonds of a given endohedral metallofullerene based on a simple evaluation of the cage structure. The predictions based on the PAC are fully confirmed by both the computational and experimental exploration of the Bingel-Hirsch reaction of Sc3N@D5h -C80, thus indicating that these rules are rather general and applicable to other isolated pentagon rule endohedral metallofullerenes.

Tether‐Directed Bisfunctionalization Reactions of C60 and C70

Four easily isolable regio- and stereoselective bis-adducts of C60 and C70 , as well as a new C70 -dumbbell derivative, have been synthesized by using two different bismalonate tethered moieties. The derivatives that possess relatively long-tethered moieties show highly symmetric addition patterns, as evidenced by spectroscopic measurements, whereas the derivatives possessing the shorter-tethered moiety exhibit interesting addition patterns on C60 and C70 .

[5,6]‐Open Methanofullerene Derivatives of Ih‐C80

The synthesis of novel endohedral metallofullerene (EMF) derivatives has attracted considerable attention, mainly because of their exceptional electronic properties. The exploration of new derivatization protocols to increase their solubility and processability is crucial to expand the range of potential applications of these compounds. In general, EMFs show low reactivity owing to the pronounced stabilization that results from extensive charge transfer between the encapsulated metal cluster and the carbon cage. It is wellknown that cycloaddition reactions, such as 1,3-dipolar cycloaddition reactions of azomethine ylides, Diels–Alder reactions, and [2+2] cycloaddition reactions, proceed well with trimetallic nitride endohedrals only if a large excess of the reagents and long reaction times are used. An interesting observation concerning the most studied EMF, Sc3N@Ih-C80, is its lack of reactivity under regular Bingel–Hirsch conditions. Sc3N@Ih-C80 reacts only in the presence of dimethyl formamide. Cyclopropanation-type reactions have been used to modify EMFs to yield methanofullerenes and recently, azafulleroids and silylene-bridged derivatives. There are two distinct addition sites available on the Ih isomer of C80 fullerenes: C C bonds at [6,6] ring junctions (pyrene-type sites) and C C bonds at [5,6] ring junctions (corannulenetype sites). In 2005, Poblet and co-workers reported that the corannulene [5,6] bonds closest to the Sc atoms have the highest strain of all bonds in the Ih-C80 cage. Reactions at this bond can relieve some of the strain and produce the thermodynamically more stable derivative; therefore, the [5,6] bond is more reactive toward exohedral functionalization. This hypothesis was experimentally corroborated for reactions such as Diels–Alder and 1,3-dipolar cycloaddition reactions. However, the [6,6] junction is favored for methano-bridge formation on Ih-C80. [13, 19, 20] Although nitrogen and silicon bridges at [5,6] bonds have been reported, the corresponding methano adducts have remained elusive. Phenyl-C61-butyric acid methyl ester (PC61BM) and phenyl-C71-butyric acid methyl ester (PC71BM) are wellknown electron acceptors that exhibit reasonable efficiencies in organic photovoltaic (OPV) devices; thus, the methano bridge is a useful anchor for the preparation of fullerene derivatives, partly because of its stability at high temperatures. There are many examples of methano derivatives of EMFs; 13, 19] the most commonly reported are derivatives of Sc3N@Ih-C80, because it is the third-most-abundant fullerene after C60 and C70. To the best of our knowledge, all reported cyclopropane derivatives of Ih-C80 were formed by addition exclusively to [6,6] bonds. The diphenylmethane (DPM) addend was first reported by Mart n et al. on C60, and these derivatives showed promising properties in organic photovoltaic (OPV) devices. Some methanofullerene derivatives of endohedral fullerenes have already shown high open-circuit voltage (Voc) with reasonable efficiencies in OPV devices. [6] Herein, we report the synthesis and characterization of six diphenylmethano derivatives of Sc3N@Ih-C80 in good yields under mild conditions. Three of the compounds, 2a–c, are the first examples of [5,6]-open methanofullerenes derived from an IhC80 cage. The structures of compounds 2c and 3 c were confirmed by X-ray crystallography. Compounds 2 and 3 were obtained by photoirradiation of the appropriate carbene precursor 1 (5 equiv) in a solution of Sc3N@Ih-C80 in o-dichlorobenzene (o-DCB) at 0 8C for 10 min (Scheme 1, route A; see the Supporting Information). The modified endofullerenes 2 and 3 were obtained in over 40% yield in all cases (> 70 % as based on the unreacted pristine starting material). The crude reaction product was purified by column chromatography on silica gel with CS2/hexanes (7:3) as the eluent to yield a monoadduct fraction and with CS2/ toluene (1:4) to yield a small fraction of bisadducts (see the Supporting Information). The matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectra

Reactivity differences of Sc3N@C2n (2n = 68 and 80). Synthesis of the first methanofullerene derivatives of Sc3N@D5h-C80

Using a purification method introduced earlier based on redox properties it was possible to isolate Sc3N@I(h)-C80 and Sc3N@D(3h)-C78 and a mixture of Sc3N@D(5h)-C80 and Sc3N@D3-C68. Taking advantage of their chemical reactivity differences, Sc3N@D(5h)-C80 was isolated from Sc3N@D3-C68 followed by further functionalization, giving rise to five new methano-derivatives of Sc3N@D(5h)-C80.

Fullerene Derivatives Strongly Inhibit HIV-1 Replication by Affecting Virus Maturation without Impairing Protease Activity.

ABSTRACT Three compounds (1, 2, and 3) previously reported to inhibit HIV-1 replication and/or in vitro activity of reverse transcriptase were studied, but only fullerene derivatives 1 and 2 showed strong antiviral activity on the replication of HIV-1 in human CD4+ T cells. However, these compounds did not inhibit infection by single-round infection vesicular stomatitis virus glycoprotein G (VSV-G)-pseudotyped viruses, indicating no effect on the early steps of the viral life cycle. In contrast, analysis of single-round infection VSV-G-pseudotyped HIV-1 produced in the presence of compound 1 or 2 showed a complete lack of infectivity in human CD4+ T cells, suggesting that the late stages of the HIV-1 life cycle were affected. Quantification of virion-associated viral RNA and p24 indicates that RNA packaging and viral production were unremarkable in these viruses. However, Gag and Gag-Pol processing was affected, as evidenced by immunoblot analysis with an anti-p24 antibody and the measurement of virion-associated reverse transcriptase activity, ratifying the effect of the fullerene derivatives on virion maturation of the HIV-1 life cycle. Surprisingly, fullerenes 1 and 2 did not inhibit HIV-1 protease in an in vitro assay at the doses that potently blocked viral infectivity, suggesting a protease-independent mechanism of action. Highlighting the potential therapeutic relevance of fullerene derivatives, these compounds block infection by HIV-1 resistant to protease and maturation inhibitors.

Transformation of doped graphite into cluster-encapsulated fullerene cages

An ultimate goal in carbon nanoscience is to decipher formation mechanisms of highly ordered systems. Here, we disclose chemical processes that result in formation of high-symmetry clusterfullerenes, which attract interest for use in applications that span biomedicine to molecular electronics. The conversion of doped graphite into a C80 cage is shown to occur through bottom-up self-assembly reactions. Unlike conventional forms of fullerene, the iconic Buckminsterfullerene cage, Ih-C60, is entirely avoided in the bottom-up formation mechanism to afford synthesis of group 3-based metallic nitride clusterfullerenes. The effects of structural motifs and cluster–cage interactions on formation of compounds in the solvent-extractable C70–C100 region are determined by in situ studies of defined clusterfullerenes under typical synthetic conditions. This work establishes the molecular origin and mechanism that underlie formation of unique carbon cage materials, which may be used as a benchmark to guide future nanocarbon explorations.An understanding of how caged carbon materials self-assemble from doped graphite is a long-standing challenge. Here, the authors show that distinct bottom-up processes lead to the synthesis of high-symmetry clusterfullerenes.

CCDC 1437434: Experimental Crystal Structure Determination

Related Article: Maira R. Ceron, Marta Izquierdo, Amineh Aghabali, Sophie P. Vogel, Marilyn M. Olmstead, Alan L. Balch, Luis Echegoyen|2016|Carbon|105|394|doi:10.1016/j.carbon.2016.04.044