Fullerene-mixed Peroxide Research Articles

Concise Synthesis of Open-Cage Fullerenes for Oxygen Delivery.

Open-cage fullerenes with a 19-membered orifice were prepared in three steps from C60 . The key step for cage-opening is aniline mediated ring expansion of a fullerene-mixed peroxide with a ketolactone moiety on the orifice. Release of ring strain on the spherical fullerene cage served as the main driving force for the efficient cage-opening sequence. Encapsulation of oxygen could be achieved at room temperature under moderate pressure (50 atm) and the encapsulated oxygen could be released slowly under ambient conditions. The activation energy of the oxygen-releasing process is 18.8 kcal mol-1 and the half-life at 37 °C was 73 min, which makes this open-cage fullerene derivative a potential oxygen-delivery material.

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.

Synthesis of Metal Complexes with an Open-Cage Fullerene as the Ligand.

An open-cage C60 derivative 9 with anilino, hemiketal, and lactone moieties on the edge of the opening was prepared through a fullerene-mixed peroxide procedure. Key steps include decarbonylation, intramolecular Friedel-Crafts reaction and oxetane ring opening rearrangement. The open-cage compound 9 readily reacts with various metal salts. A nickel complex was obtained by treating 9 with NiCl2 at r.t. followed by purification on a silica gel column. Single-crystal X-ray diffraction analysis showed that the nickel ion is coordinated to two ligands with an octahedral geometry.

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

AbstractReview: [49 refs.

Peroxide-mediated selective cleavage of [60]fullerene skeleton bonds: towards the synthesis of open-cage fulleroid C55O5.

Replacement of a pentagon in [60]fullerene with five oxygen atoms yields the open-cage compound C55O5 with five carbonyl groups on the rim of the orifice. Our attempts to synthesize such a target molecule starting from C60 have led us to prepare the fullerene-mixed peroxides such as C60(OO-t-Bu)6 with all the peroxo addends surrounding the same pentagon. Further investigations of the peroxide chemistry have generated various open-cage fullerene derivatives, including the carbon monoxide encapsulated endohedral compound CO@C59O6. This Personal Account mainly discusses peroxide-based processes resulting in selective cleavage of the fullerene skeleton bonds.

Selective Synthesis of Fullerenol Derivatives with Terminal Alkyne and Crown Ether Addends

A series of isomerically pure alkynyl-substituted fullerenol derivatives such as C(60)(OH)(6)(O(CH(2))(3)CCH)(2) were synthesized through Lewis acid catalyzed epoxy ring opening and/or S(N)1 replacement reactions starting from the fullerene-mixed peroxide C(60)(O)(t-BuOO)(4). Copper-catalyzed azide-alkyne cycloaddition readily converted the terminal alkynyl groups into triazole groups. Intramolecular oxidative alkyne coupling afforded a fullerenyl crown ether derivative.

Synthesis of 18-Membered Open-Cage Fullerenes through Controlled Stepwise Fullerene Skeleton Bond Cleavage Processes and Substituent-Mediated Tuning of the Redox Potential of Open-Cage Fullerenes

Oxidation of the fullerenediol C(60)(OH)(2)(O)(OAc)(OOtBu)(3) with PhI(OAc)(2) yields the open-cage fullerene derivative C(60)(O)(2)(O)(OAc)(OOtBu)(3)2 with an 11-membered orifice. Compound 2 reacts with aniline to form a new open-cage derivative with a 14-membered orifice, which yields an 18-membered open-cage fullerene derivative upon addition of another molecule of aniline. Two different types of aniline derivatives with either electron-donating or electron-withdrawing substituents can be added sequentially, affording an unsymmetrical moiety in the open-cage structure. Reduction potentials of the 18-membered open-cage fullerene derivatives can be fine-tuned by changing the substituents on the aniline. The results provide new insights about the mechanism of open-cage reactions of fullerene-mixed peroxide.

Preparation of Ketolactone and Bislactone [60]Fullerene Derivatives and Their Conversion into Open‐Cage Fullerenes with a 12‐ or 15‐Membered Orifice

AbstractSelective cleavage of the peroxo group in the fullerene mixed peroxide C60(O)(OOtBu)6 1 produces open‐cage fullerenes with ketone and lactone moieties on the rim of the orifice. Photolysis of 1 results in the ketolactone derivative 2 C58(CO)‐(COO)(O)(OOtBu)4 with an epoxide moiety. Thermolysis of 1 results in the formation of two other isomers, the bislactone 3 C58(COO)2(OOtBu)4 and the ketolactone 4 C58(CO)(COO)(O)(OOtBu)4 with a 1,4‐dioxepin‐5‐one moiety. Both alcohols and amines react with one of the lactone moieties of 3 and expand the 12‐membered orifice into a 15‐membered orifice. Only amines react with the lactone moiety of 4 and expand the 11‐membered orifice into a 12‐membered orifice. Total yield of the 15‐membered open‐cage compound can reach 8.9 % in three steps starting from C60. The products were characterized by spectroscopic data and X‐ray diffraction data.

Preparation of a 12-Membered Open-Cage Fullerendione through Silane/Borane-Promoted Formation of Ketal Moieties and Oxidation of a Vicinal Fullerendiol

[60]Fullerene mixed peroxide C(60) (OH)(Cl)(OOtBu) reacts with PhMe(2)SiH/B(C(6)F(5))(3) to give oxahomofullerene. Mechanistic investigation indicates that the hydroxyl group in the central pentagon ring is essential to convert the tert-butylperoxo group into a ketal moiety. Migration of the silyl group and transformation of the siloxy group into a phenyl group are observed in the deprotection of the fullerene bound siloxy group. A 12-membered open-cage fullerendione was obtained through oxidation of a [6,6]-fullerendiol. This orifice could be closed to form ketal/hemiketal moieties by BF(3)-catalyzed reaction with methanol. All of the new fullerene derivatives were characterized by spectroscopic data, and structure of the open-cage fullerendione was also confirmed by single-crystal X-ray analysis.

Efficient Cage-Opening Cascade Process for the Preparation of Water-Encapsulated [60]Fullerene Derivatives

Cage-opened fullerenes with 18-membered-ring orifices have been prepared starting from fullerene-mixed peroxides. The key transformation involves a cascade sequence including a deketalization, a S(N)2' epoxide opening reaction, and a formal 3,3-sigma rearrangement. The 18-membered-ring orifice is big enough for water encapsulation under mild conditions. Single crystal X-ray structures were obtained for both the empty and water-encapsulated fullerene derivatives.

Preparation of Azafullerene Derivatives from Fullerene-Mixed Peroxides and Single Crystal X-ray Structures of Azafulleroid and Azafullerene

Azafullerene was prepared by addition of hydroxylamine to a cage-opened fullerendione derivative and subsequent PCl5 induced rearrangement processes. X-ray structures were obtained for the azafullerene and its azafulleroid precursor.

Preparation of fullerenol, fullerenone, and aminofullerene derivatives through selective cleavage of fullerene C–H, C–C, C–N, and C–O bonds in fullerene-mixed peroxide derivatives

Various reactions of fullerene-mixed peroxides were investigated in an effort to explore the chemistry of functional groups on the fullerene surface. Amines convert fullerene peroxides into fullerene epoxides through S N2′ type reaction. Lewis acid catalyzed hydrolysis of fullerene epoxides led to vicinal fullerendiols, which may be oxidized into fullerendiones by diacetoxyiodobenzene (DIB). Alcohols and amines react with the adjacent dione to form acetal or hemiacetal groups through different mechanisms.

Reactivity of Fullerene Epoxide: Preparation of Fullerene-Fused Thiirane, Tetrahydrothiazolidin-2-one, and 1,3-Dioxolane

The epoxide moiety in the fullerene-mixed peroxide C60(O)(OOtBu)4 1 reacts readily with aryl isocyanates ArNCS (Ar = Ph, Naph) to form both the thiirane derivative C60(S)(OOtBu)4 and fullerene-fused tetrahydrothiazolidin-2-one. The reaction of 1 with trimethylsilyl isothiocyanate TMSNCS yields the isothiocyanate derivative C60(NCS)(OH)(OOtBu)4, the isothiocyanate and hydroxyl moieties of which could be converted to a fullerene-fused tetrahydrothiazolidin-2-one ring with alumina quantitatively. Treating 1 with BF3.Et2O yields the fullerene-fused [1,3,2]-dioxoborolane derivative C60(O2BOH)(OOtBu)4. In the presence of aldehyde or acetone, BF3.Et2O catalyzes the conversion of epoxide to fullerene-fused 1,3-dioxolane derivatives. The products are characterized by spectroscopic data. Two of the compounds are also characterized by single-crystal X-ray analysis.

Controlled regio- and chemoselective addition of isothiocyanate to the dione moiety of a cage-opened fullerene-mixed peroxide derivative

Addition of the ambident SCN group to a fullerendione derivative follows two different pathways in the presence and absence of Lewis acid.

Synthesis of [59]Fullerenones through Peroxide-Mediated Stepwise Cleavage of Fullerene Skeleton Bonds and X-ray Structures of Their Water-Encapsulated Open-Cage Complexes

Fullerene skeleton modification has been investigated through selective cleavage of the fullerene carbon-carbon bonds under mild conditions. Several cage-opened fullerene derivatives including three [59]fullerenones with an 18-membered-ring orifice and one [59]fullerenone with a 19-membered-ring orifice have been prepared starting from the fullerene mixed peroxide 1, C60(OOtBu)6. The prepositioned tert-butyl peroxy groups in 1 serve as excellent oxygen sources for formation of hydroxyl and carbonyl groups. The cage-opening reactions were initiated by photoinduced homolysis of the tBu-O bond, followed by sequential ring expansion steps. A key step of the ring expansion reactions is the oxidation of adjacent fullerene hydroxyl and amino groups by diacetoxyliodobenzene (DIB). Aminolysis of a cage-opened fullerene derivative containing an anhydride moiety resulted in multiple bond cleavage in one step. A domino mechanism was proposed for this reaction. Decarboxylation led to elimination of one carbon atom from the C60 cage and formation of [59]fullerenones. The cage-opened [59]fullerenones were found to encapsulate water under mild conditions. All compounds were characterized by spectroscopic data. Single-crystal structures were also obtained for five skeleton-modified derivatives including two water-encapsulated fulleroids.

Efficient Conversion of Bromofullerene to Alkoxyfullerenes Through Either Homolytic or Heterolytic Cleavage of C60—Br Bond.

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Efficient conversion of bromofullerene to alkoxyfullerenes through either homolytic or heterolytic cleavage of C 60–Br bond

The bromine atom in a fullerene-mixed peroxide derivative is replaced by an alkoxyl group under visible light irradiation or in the presence of silver salt. Homolytic or heterolytic cleavage of the C 60–Br bond is proposed to explain the mechanism. The presence of oxygen is also a key factor in the photolysis reaction.

From Fullerene-Mixed Peroxide to Open-Cage Oxafulleroid C59(O)3(OH)2(OOtBu)2 Embedded with Furan and Lactone Motifs

[reaction: see text] Removal of one carbon atom from the C60 cage is achieved under mild conditions. The process involves the formation of fullerene-mixed peroxide, subsequent Lewis acid induced cleavage of O-O and C-O bonds, and thermolysis at 75 degrees C. In the proposed mechanism, the carbon atom is deleted as CO and an oxygen atom occupies the vacancy to form a furan ring. Single-crystal X-ray analysis confirmed the results.

Lewis Acid Promoted Preparation of Isomerically Pure Fullerenols from Fullerene Peroxides C60(OOt-Bu)6 and C60(O)(OOt-Bu)6

Fullerene mixed peroxides C60(t-BuOO)6 and C60(O)(t-BuOO)6 react with Lewis acids to form various fullerenols through the partial fragmentation of t-BuOO groups. Two monohydroxyl fullerenols with the general formula C60(OH)(t-BuOO)5 and six monohydroxyl fullerenols with the general formula C60(O)(OH)(t-BuOO)5 were prepared, which are essentially the same except the location of the OH group. An additional reaction of the monohydroxyl fullerenols gave bis- and trishydroxyl fullerenols. Single-crystal X-ray structures have been obtained for the two monohydroxyl fullerenols. Other compounds are characterized by chemical correlation and their spectroscopic data. Cuprous bromide could protect the most reactive t-BuOO group from being attacked by stronger Lewis acids. The proposed mechanism mainly involves Lewis acid induced heterolysis of the peroxo O-O bond.

Preparation of Covalent-Bound Iodofullerene through Selective Opening of Fullerene Epoxide To Form Halohydrin Fullerene Derivatives

The epoxy moiety in a fullerene mixed peroxide can be opened regioselectively by various Lewis acids to form halohydrin fullerene derivatives. The first iodofullerene was obtained by treating the fullerene epoxide with triphenylphosphine and iodine. A single-crystal structure of the chlorohydrin derivative supports the results.