Regio- and diastereo-controlled synthesis of bis(formylmethano)[60]fullerenes and their application to the formation of [60]fullerene pearl-necklace polyimines

The tether-directed method was firstly applied to the biscyclopropanation of [60]fullerene via the addition-elimination reaction of bis(sulfonium ylide)s to give bis(formylmethano)[60]fullerenes with satisfactory regio- and stereoselectivity. The equatorial-bisadduct thus obtained was used for the polycondensation with an aromatic diamine to afford the corresponding pearl-necklace polyimine with satisfactorily high degree of polymerization.     

Highly regioselective transformation of out/out-equatorial bis(formylmethano)[60]fullerenes: construction of dissymmetric [60]fullerene-centered triads

Three kinds of out/out-equatorial bis(formylmethano)[60]fullerenes (1b-d) were obtained by the tether-directed bifunctionalization of [60]fullerene with bis(alpha-formylsulfonium ylide)s. The condensation of aromatic amines with 1b-d proceeded with an unexpectedly high regioselectivity to give one of two possible regioisomers of mono-imines as the main products (the ratio of the regioisomers, up to 97:3). By the transformation of the remaining formyl group in the mono-imines thus obtained, the corresponding dissymmetric bis-imines were efficiently synthesized.     

Revisit to the reaction of [60]fullerene with nitrile ylides generated from imidoyl chlorides and triethylamine

The reaction of [60]fullerene (C₆₀) with nitrile ylides generated from N-benzyl-4-nitrobenzimidoyl chloride/N-(4-chlorobenzyl)-4-nitrobenzimidoyl chloride and triethylamine gave only isomeric monoadducts of C₆₀ with [6,6]-closed structure. No [5,6]-open adduct of C₆₀ could be identified from these reactions. The previously reported [5,6]-open product of C₆₀ should be reassigned as a [6,6]-closed product.     

Probing the spatial requirements for [60]fullerene-[60]fullerene π-stacking and the syn addition of [60]fullerenes across acenes

The reaction between 2 equiv of [60]fullerene and 6,8,15,17-tetraphenylheptacene-7,16-quinone leads to both cis and trans-bis[60]fullerene adducts. This result contrasts sharply with the highly diastereoselective syn additions of [60]fullerenes across 6,13-diphenylpentacene and 6,8,15,17-tetraphenylheptacene. The importance of spatially dependent [60]fullerene-[60]fullerene π-stacking interactions in promoting a syn addition of [60]fullerenes is discussed.     

Regio/diastereo-controls of the Bingel-type biscyclopropanation of [60]fullerene by using bismalonates with a Tröger base analogue-derived tether

Four kinds of bismalonates tethered with a Tröger base derivative were synthesized and used for the double Bingel reaction of [60]fullerene. The regio/diastereoselectivities of the reaction were highly influenced by the structure of the Tröger base derivatives. Heteroaromatic analogues of the Tröger base were found to be applicable as the core of the tether.     

Regioselective synthesis of tetra(aryl)-mono(silylmethyl)[60]fullerenes and derivatization to methanofullerene compound

A method for the facile synthesis of tetraaryl-trimethylsilylmethyl-hydro[60]fullerenes, C₆₀Ar₄(CH₂SiMeR)H, has been developed in which readily prepared anionic mono(silylmethyl) fullerene is subjected to reaction conditions for organocopper-mediated multiple addition. Penta(organo)fullerene derivatives bearing different substituents and diverse functionality were synthesized in moderate to good yield under simple and mild reaction conditions. Further organic and organometallic transformations of these fullerenes allowed us to synthesize transition-metal complexes and a new methanofullerene derivative, 1,9-methano-6,12,15,18-tetraphenyl[60]fullerene, C₆₀Ph₄(CH₂).     

Facile fullerene modification: FeCl3-mediated quantitative conversion of C60 to polyarylated fullerenes containing pentaaryl(chloro)[60]fullerenes

A facile, one-step reaction using inexpensive reagents has been developed for functionalization of [60]fullerene, where the reaction of C(60) with FeCl(3) in chlorobenzene proceeded at 25 °C with 100% conversion, yielding a mixture of polyarylated products containing pentaaryl(chloro)[60]fullerene, C(60)(C(6)H(4)Cl)(5)Cl (up to 29%) and other polyarylated fullerenes (number of aryl groups is in a range from 5 to 10).     

Thermal and catalytic reactions of ethyl diazopyruvate with [60]fullerene

New stable [6,6]-methano cycloadducts and fulleropyrazolines containing electron-withdrawing groups have been obtained by the reaction of ethyl diazopyruvate with [60]fullerene. The results obtained by a systematic study conducted both in thermal and catalytic conditions have provided crucial indications concerning the mechanism of this important cluster opening process in fullerene chemistry.     

A spectrophotometric study of the charge transfer complexes of [60]fullerene with different tert-butylcalix[4]crowns

Formation of the charge-transfer complexes between various calix[4]crowns (1-4) and [60]fullerene were studied in toluene solution using UV-vis spectrophotometry. The stability constants and the thermodynamic data of the resulting 1:1 complexes were determined and were found to decrease with increasing the size of the crown moiety of the calixcrown. Except the complex of 3, all the complexes were found to be enthalpy stabilized but disfavored in terms of entropy.     

A biphasic displacement of [60]fullerene from fac-(dihapto-[60]fullerene)(dihapto-1,10-phenanthroline) tricarbonyl molybdenum (0)

The Lewis bases (=L) triphenylphosphine (PPh₃) and tricyclohexyl phosphine (P(Cy)₃) displace [60]fullerene (C₆₀) from the complex fac-(η²-C₆₀)(η²-phen)Mo(CO)₃ (phen = 1,10-phenanthroline). The progress of the reactions was followed observing the decrease of the absorbance values at 440 nm and by monitoring the stretching carbonyl region from 1700 to 2100 cm⁻¹. The plots of absorbance vs. time were biexponential, indicative of a biphasic behavior, for reactions under flooding conditions where [L] ? [fac-(η²-C₆₀)(η²-phen)Mo(CO)₃]. The plot of absorbance vs. time consisted of two consecutive segments: the first segment of the plot was a decrease of absorbance with time followed by a second segment where the absorbance increased with time. The first segment of the biphasic plot was ascribed to the solvent-assisted displacement of C₆₀ from fac-(η²-C₆₀)(η²-phen)Mo(CO)₃ and the second segment to decomposition of the complex fac-(η¹-L)(η²-phen)Mo(CO)₃ produced in the first of the two consecutive reactions. The rate constant values corresponding to the first segment of the biphasic plot are independent of the chemical nature of L, the molar concentration of L, and the molar concentration of C₆₀ but dependent on the chemical nature of the solvent.     

Perylene-3,4:9,10-bis(dicarboximide) linked to [60]fullerene as a light-harvesting antenna

New [60]fullerene-perylene-3,4:9,10-bis(dicarboximide) dyads 1 and 2 are described in the search of an energy transfer from the dye as a photoactive antenna to the fullerene moiety.     

Cyclodextrin-[60]fullerene conjugates: synthesis, characterization, and electrochemical behavior

Three different functionalized β-cyclodextrins (β-CDs) bearing the C₆₀ moiety linked covalently have been prepared in good yields by reaction between the parent β-CD and [60]fullerene via 1,3-dipolar cycloaddition. These compounds have been fully spectroscopically characterized and their electrochemical behavior has been investigated. Surprisingly, the electrochemical properties of the C₆₀ cage remain unaltered even after chemical functionalization, making these systems very appealing as supramolecular hosts for electron-transfer processes.     

Synthesis of a proline-rich [60]fullerene peptide with potential biological activity

A proline-rich [60]fullerene peptide was synthesized by use of (i) a 1,3-dipolar cycloaddition of an N-substituted glycine derivative to [60]fullerene, (ii) esterification of the isolated alcohol with the C-terminal amino acid of the desired peptide sequence, and finally (iii) coupling of the remaining hexapeptide to give the final product 8 as a TFA salt, with oxidized methionine. Product 8 was found to be biologically active against sera from MCTD and SLE patients (ELISA experiment).     

Methylation of [76]fullerene and [84]fullerenes; the first oxahomo derivatives of a higher fullerene

Methylation of [76]fullerene by reaction with Al-Ni alloy/NaOH followed by quenching of the intermediate anions with methyl iodide gives a mixture of methylated and methylenated products together with oxide derivatives. The major derivatives are five isomers of C(76)Me(2)(one of C(s) symmetry due to 1,6-C(76)Me(2)) and C(76)(CH(2))(n)(n= 2-4), together with corresponding mono-oxides. The single line (1)H NMR spectrum of mono-oxide C(76)Me(2)O shows it is an oxahomofullerene (ether) the first example derived from [76]fullerene, oxygen being inserted between the CMe groups in 1,6-C(76)Me(2)giving a product of C(2) symmetry. The probable structures of the unsymmetrical dimethyl derivatives have been deduced from heats of formation calculated by AM1 and density functional methods. Bis-oxide C(76)Me(4)O(2) is the first bis oxahomo[76]fullerene to be isolated and gives two equal-intensity lines in the (1)H NMR spectrum showing that it must also have C(2) symmetry; probable structures are considered. Methylation of [84]fullerene takes place less readily and only four C(84)Me(2) derivatives were isolated, two of them in quantities sufficient to show the symmetries as C(1), and either C(2) or C(s).     

Reactions of the electrochemically generated dianion of [60]fullerene with bulky secondary alky bromides

Reactions of the electrochemically generated dianion of [60]fullerene (C₆₀^2?) with bulky secondary alkyl bromides exhibit different reaction behaviors. Reaction of C₆₀^2? with diphenylbromomethane gives rise to 1,2-C₆₀HR or 1,4-C₆₀R₂ (R?=?CHPh₂) adducts, while reaction of C₆₀^2? with diethyl 2-bromomalonate unexpectedly affords methanofullerene C₆₀?>?CR₂ (R?=?CO₂Et). Plausible reaction mechanisms have been proposed to explain the formation of the observed products.     

Ligand exchange reactions of fac -(dihapto-[60]fullerene) (dihapto-1,2- bis -(diphenylphosphino)ethane tricarbonyl chromium(0)

The complex fac-(η²-C₆₀)(η²-dppe)Cr(CO)₃ (dppe?=?1,2-bis(diphenylphosphino)ethane and C₆₀?=?[60]fullerene) reacts with piperidine (pip) to produce fac-(η²-C₆₀)(η¹-pip)₂Cr(CO)₃. The reactions are first order with respect to [?fac-(η²-C₆₀)(η²-dppe)Cr(CO)₃] under flooding conditions where [pip]???[?fac-(η²-C₆₀)(η²-dppe)Cr(CO)₃]. The pseudo-first order rate constant values (k _obsd) are [pip]-dependent. Curved (upward) plots of k _obsd versus [pip] and linear plots of k _obsd versus [pip]² indicate that the piperidine-assisted dppe displacement from fac-(η²-C₆₀) (η²-dppe)Cr(CO)₃ is second order with respect to [pip]. The proposed mechanism involves a [60]fullerene-stabilized intermediate.     

Supramolecular complexation studies of [60]fullerene with calix[4]naphthalenes—a reinvestigation

Estimations of equilibrium or association constant (K_ASSOC) values reported by many other groups for the supramolecular complexation between [60]fullerene (‘C₆₀’) with different macrocyclic hosts, in solvents such as toluene or carbon disulfide, for example, is often conducted by UV-vis absorption and/or ¹H NMR spectroscopy. In this paper, the complexation behaviour of two calix[4]naphthalene hosts with C₆₀ in toluene and carbon disulfide has been re-examined, using both of these methods. An analysis is presented of the data newly obtained, in light of recent advances and understanding published by others of the limitations of, in particular, the absorption spectroscopic methods. The discussion presented is also intended to aid those who may be unfamiliar with the nuances and limitations of the analytic models involving C₆₀ supramolecular complexation. Also presented is a general mechanism for C₆₀ supramolecular complexation studies, which lay the groundwork for further experiments.     

Synthesis of fulleropyrrolidines through the reaction of [60]fullerene with quaternary ammonium salts and amino acids

The reactions of [60]fullerene with amino acids and quaternary ammonium salts in toluene afforded two fulleropyrrolidine derivatives. One fulleropyrrolidine derivative contained a RCH moiety originating from quaternary ammonium salts through C–N bond cleavages and other fulleropyrrolidine derivatives contained a PhCH moiety originating from toluene through C–H bond cleavage. By using chlorobenzene instead of toluene as solvent, only one fulleropyrrolidine derivative containing a RCH moiety was obtained in the reactions.     

Cobalt-catalyzed hydroalkylation of [60]fullerene with active alkyl bromides: selective synthesis of monoalkylated fullerenes

The Co-catalyzed hydroalkylation of C(60) with reactive alkyl bromides 1 (RBr) in the presence of Mn reductant and H(2)O at ambient temperature gave the monoalkylated C(60) (2) in good to high yields. The use of CoLn/Mn/H(2)O under Ar atmosphere is crucial for the success of the present transformation. The reaction most probably proceeds through the Co(0 or I) complex-promoted generation of a radical (R(?)) followed by addition to C(60). This hydroalkylation method was applied to the synthesis of zinc porphyrin attached C(60) (2l), dendrimer attached C(60) (2m), and fullerene dimer (2n), which were not easily available through the previously known methods.     

The first synthesis of a methano[60]fullerene with an electron-donating group at the methano-bridge carbon: synthesis and reaction of aminomethano[60]fullerene

[reaction: see text] Aminomethano[60]fullerene was synthesized for the first time as a trifluoromethanesulfonic acid salt by applying the Curtius rearrangement of azidocarbonylmethano[60]fullerene as the key reaction. Aminomethano[60]fullerene thus obtained was found to be able to react with various acyl chlorides to afford the corresponding amides.