Peroxide-Mediated Selective Cleavage of [60]Fullerene Skeleton Bonds: Towards the Synthesis of Open-Cage Fulleroid C55O5

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.

Open-cage fullerenes as ligands for metals

The remarkable structures of open-cage fullerenes with functionalization on the outer surface and an accessible inner void make them interesting ligands for reactions with metal complexes. The behaviors of open-cage fullerenes in reactions with various metal complexes are examined and compared to the corresponding reactions with intact fullerenes. The structural results from X-ray diffraction are emphasized. Open-cage fullerenes frequently undergo unanticipated structural changes such as carbon-carbon bond cleavage upon reactions with metal complexes. Much more remains to be learned about the possibility of inserting metal ions larger than Li+ into the interior void of these open-cage fullerenes and about the effects of redox reactions on metal complexes of open-cage fullerenes.

Electrochemically Promoted Benzylation of [60]Fullerooxazolidinone

Benzylation of the electrochemically generated dianion from N-p-tolyl-[60]fullerooxazolidinone with benzyl bromide provides three products with different addition patterns. The product distribution can be dramatically altered by varying the reaction conditions. Based on spectral characterizations, these products have been assigned as mono-benzylated 1,4-adduct and bis-benzylated 1,2,3,16- and 1,4,9,25-adducts, respectively. The assigned 1,2,3,16-adduct has been further established by X-ray diffraction analysis. It is believed that the 1,4-adduct is obtained by decarboxylative benzylation of the dianionic species, while bis-benzylated 1,2,3,16- and 1,4,9,25-adducts are achieved via a rearrangement process. In addition, the electrochemical properties of these products have been studied.

An "Umpolung Relay" Strategy: One-Pot, Twice Polarity Inversion Cascade Synthesis of Diversified [60]Fulleroindoles

An "umpolung relay" strategy, which includes an one-pot, twice polarity inversion cascade of C₆₀ via carbanion and carbocation polarity reversed relay pathway, has been developed for the synthesis of a diverse range of novel [60]fulleroindole derivatives.

Electrochemical regioselective alkylations of a [60]fulleroindoline with bulky alkyl bromides

Electrochemical alkylations of a [60]fulleroindoline with different bulky alkyl bromides exhibit different reaction behaviors. The hydroalkylation and dialkylation of the electrochemically generated dianionic [60]fulleroindoline with bulky 2,4,6-tris(bromomethyl)mesitylene give rise to 1,2,3,16-adducts. In comparison, the hydroalkylation of the dianionic [60]fulleroindoline with bulkier diphenylbromomethane still affords a 1,2,3,16-adduct, while the corresponding dialkylation provides a sterically favoured 1,4,9,12-adduct, which is scarcely investigated, as the major product along with the isomeric 1,2,3,16-adduct as the minor product. The structures of these products have been determined by spectroscopic data and single-crystal X-ray diffraction analysis. A plausible reaction mechanism has been proposed to explain the formation of the observed products.

Synthesis of Open-Cage [60]Fullerenes with Five Carbonyl Groups on the Rim of the 15-Membered Orifice

A new type of open-cage [60]fullerene was prepared starting from our previously reported open-cage [60]fullerenes containing hydroxy and tert-butylperoxo groups, and an iminofuranone moiety on the rim of the orifice. The key reactions are alcoholysis with MeOH/PCl₅ and reductive aromatization with SnCl₂ or HI (aq). The resulting open-cage compound contains two ketone carbonyls, two amide carbonyls, and one ester carbonyl group. The X-ray crystal structure of the precursor compound shows that the 18-membered orifice is almost completely blocked because of the presence of the amide group directly above the orifice.

Potassium salt promoted regioselective three-component coupling synthesis of 1,4-asymmetrical [60]fullerene bisadducts with superior electron transport properties

An efficient one-pot three-component domino coupling reaction of phenols, C₆₀, and bromoalkanes was developed, resulting in the highly regioselective synthesis of 1,4-asymmetrical C₆₀ bisadducts.

Molecular Containers Derived from [60]Fullerene through Peroxide Chemistry

Molecular containers can keep guest molecules in a confined space that is completely separated from the solution. They have wide potential applications, including selective trapping of reactive intermediates, catalysis within the cavity, and molecular delivery. Numerous molecular containers have been prepared through covalent bonds, metal-ligand interactions and H-bonding or hydrophobic interactions. Fullerenes are all-carbon molecules with a spherical structure. Partial opening of the cage structure results in open-cage fullerenes, which can serve as molecular containers for various small molecules and atoms. Compared with classical molecular containers, open-cage fullerenes exhibit some unusual phenomena because of the unique structure of the fullerene cage. The synthesis of an open-cage fullerene with a large enough orifice as a molecular container requires consecutive cleavage of multiple fullerene skeleton bonds within a local area on the cage surface. In spite of the difficulty, remarkable progress has been achieved. Several reactions have been reported to cleave fullerene C-C bonds selectively to form open-cage fullerenes, some of which have been successfully used as molecular containers for molecules such as H₂O. The size and shape of the orifice play a key role in the encapsulation of the guest molecule. To date the focus in this area has been the preparation of open-cage fullerenes and encapsulation of small molecules. Little information has been reported about the functional properties of these host-guest systems. Potential applications of these systems need to be explored. This Account mainly presents our results on the encapsulation of small molecules in open-cage fullerenes prepared in my group. The preparation of our open-cage fullerenes is based on fullerene-mixed peroxides, which are briefly mentioned herein. The encapsulation and release of a single molecule of water is discussed in detail. Quantitative water encapsulation was achieved by heating the open-cage fullerene in a homogeneous CDCl₃/H₂O/EtOH mixture at 80 °C for 18 h. The kinetics of the water release process was studied by blackbody IR radiation-induced dissociation (BIRD) and theoretical calculations. The trapped water could also be released by H-bonding with HF. To control the encapsulation and release processes, we prepared open-cage fullerenes with a switchable stopper on the rim of the orifice. Besides H₂O, encapsulations of H₂, HF, CO, O₂, and H₂O₂ were also achieved by using different open-cage fullerenes. The encapsulation of CO is quite unusual in that the trapped CO is derived from a fullerene skeleton carbon that was pushed into the cavity by oxidation under ambient conditions at room temperature. The trapped O₂/H₂O₂ could be released slowly under mild conditions, and these systems are now being studied as a new type of oxygen-releasing materials for biomedical research. The present results demonstrate that open-cage fullerenes are suitable molecular containers for small molecules. Our future work will focus on optimizing the conditions for the preparation of open-cage fullerenes and applications of open-cage fullerenes in areas such as oxygen delivery for photodynamic therapy.

A retro Baeyer-Villiger reaction: electrochemical reduction of [60]fullerene-fused lactones to [60]fullerene-fused ketones

An unprecedented retro Baeyer–Villiger reaction has been achieved by the electrochemical reduction of [60]fullerene-fused lactones in the presence of acetic acid at room temperature, affording [60]fullerene-fused ketones in excellent yields within a short time.

A highly efficient electrochemical reduction of [60]fullerene-fused lactones to [60]fullerene-fused ketones, a formal process of retro Baeyer–Villiger reaction, has been achieved for the first time. The electrochemically generated dianionic [60]fullerene-fused lactones can be transformed into [60]fullerene-fused ketones in the presence of acetic acid in 85–91% yields. Control experiments have been performed to elucidate the reaction mechanism. The products have been characterized with spectroscopic data and single-crystal X-ray analysis. Moreover, the electrochemical properties have also been investigated.

Solvent-promoted catalyst-free regioselective N-incorporation multicomponent domino reaction: rapid assembly of π-functionalized [60]fullerene-fused dihydrocarbolines

An unprecedented solvent-promoted N-incorporation multicomponent domino chemistry was developed for the direct construction of π-functionalized [60]fullerene-fused dihydrocarbolines from simple hydrocarbons.

Synthesis and reactivity of tetraalkoxyl[60]fullerene epoxides, C60(O)(OR)4

Hexachloro[60]fullerene, C60Cl6, was reacted with a mixture of ROH/H2O (R = Me, Et, n-Pr, (CH2)2C≡CH) to form both C60Cl(OH)(OR)4 and C60Cl(OR)5. Only the C60Cl(OH)(OR)4 were isolated with bulky alcohols, ROH (R = (CH2)3C≡CH, (CH2)4C≡CH). Tetrahydro[60]fullerene epoxides, C60(O)(OR)4, were prepared by treating C60Cl(OH)(OR)4 with CuI. The epoxy moiety could be hydrolyzed to the vicinal diol derivatives, C60(OH)2(OR)4, and then oxidized to form dicarbonyl open-cage fullerenes, C60O2(OR)4. CuI was found to convert the terminal alkynyl addends into iodoalkynyl addends on the C60 cage.

Oxidative deamination of azafulleroids into C60 by peracids

Oxidation of azafulleroids with peracids regenerate C₆₀via oxidation of the bridged nitrogen, depending on the basicity of N-substituents.