Methanofullerenes, derivatives

A methanofullerene derivative possessing an ammonium subunit has been prepared and subsequently shown to form a supramolecular complex with a porphyrin-crown ether conjugate <06T1979>. The synthesis and study of these fullerene-containing supramolecular photoactive devices have also been reported <06CRC1022>. 

Another example has been provided by Ito et al., who described the use of methanofullerene derivatives as powerful and stable precursors for glycofullerenes.217 Their study was based on the use of [60]fullerenoacetyl chloride (227), obtained from the ferf-butyl [60]fullerenoacetate derivative 226, which had been prepared in 56% yield by treatment of corresponding stabilized sulfonium ylides 225 with C6o-218 Subsequent transformation with p-TsOH in toluene gave [60]full-erenoacetic acid, which was directly converted into the corresponding acyl chloride 227 by using thionyl chloride. Standard ester formation with methyl 2,3,4-tetra-O-benzyI -/<-d-gl ucopyranoside (228) and 4-(dimethylamino)pyridine (DMAP) afforded the desired hybrid derivative 229 in 66% yield. 

The 1,3-dipolar addition reaction of fullerene with diazo compounds is one of the most studied reactions in the early stage of the research on fullerene chemistry [7]. The reaction in solution first affords rather labile fulleropyrazoline derivative 26, which is readily converted to the so-called 5,6-open (a bond originally shared by five- and six-membered rings cleaved) fulleroid (27) or 6,6-closed (a bond shared by two six-membered rings remaining closed) methanofullerene derivatives (28) by heat (e.g., refluxing in toluene) or photoirradiation (UV light), respectively (Scheme 11) [7a]. 

Let us note that two homologues of the malonate addends and of the corresponding methanofullerene derivatives described above (Fig. 66) were also prepared with chiral pendant mesogenic groups, laterally attached (Fig. 69). Both the G1 [304] and G2 [57] fullerodendrimers were found to show a chiral nematic phase (Fig. 69, Gl G 26 N 69 1 G2 G 24.3 N 80.61), and are the first Ceo derivatives that possess a chiral mesophase the Gl Geo-free malonate was also mesomorphic (G 20 N 113 I). 

First to be checked was a set of methanofullerene derivatives 289a-c, readily available via addition of substituted diarylcarbenes (generated in situ) to one of the double bonds of fullerene 59 followed by a conventional transformation of the carboxamido groups of the side chains (Scheme 4.88). Bis-succinoyl-... 

Cyclic a-diketones (acenaphthenequinone, aceanthrenequinone, and tV-alkyUsatins) were deoxygenated by tris(diethylamino)phosphine in the presence of fiillerene CgQ. a-Ketocarbenes were probable intermediates in the formation of polycyclic methanofullerene derivatives, which were investigated for their electrochemical behaviour and structures. 

The most used nucleophilic synthesis reaction to form fuUerenes is cyclopropanation. The original method was developed by Bingel, and it employs the generation of a carbon nucleophile starting from a-halo esters in the presence of a base (such as NaH), and the subsequent addition to After the addition of the anions of a-halo ester, an intramolecular substitution of the halide takes place with the intermediate fullerene anion, giving the corresponding methanofullerene derivative (Scheme 2.1e). Further modification of this method consist of preparing the a-halomalonate in situ. 

UV spectroseopy may serve as one of the qualitative and quantitative ways of fuUerene adducts analysis in such mixtures [5-7]. In literary sources there is no data on spectral characteristics of fuUerene compounds with different degrees of substitution, which allows to estimate the content of the functionalization of products in their mixtures. This paper is dedicated to the UV spectroscopy study of transformation into methanofullerene derivatives with different functionalization degrees. 

The most important classes of functionalized [60]fullerene derivatives, e.g. methanofullerenes [341, pyrrolidinofullerenes [35], Diels-Alder adducts [34i] and aziridinofullerene [36], all give rise to a cancellation of the fivefold degeneration of their HOMO and tlireefold degeneration of their LUMO levels (figure Cl.2.5). This stems in a first order approximation from a perturbation of the fullerene s 7i-electron system in combination with a partial loss of the delocalization. 

An alternative synthetic approach, first developed by Bingel225 allowed the efficient nucleophilic cyclopropanation of fullerenes via their reaction with bromomalonate derivatives in the presence of base. This approach, the most reliable method for the synthesis of functionalized methanofullerenes, combined the advantages of mild... 

Novel nitroxide malonate methanofullerenes (Fig. 1.3), thanks to the presence of nitroxide radicals and fullerene moiety, are able to protect cells from toxic side effects of cyclophosphamide (Gubskaya et al., 2007). Experiments were carried out on mice, in which leukemia P-388 was transplanted. Cyclophosphamide or fullerene individually injected did not increase the average life span of the animals, while the combination of the anticancer drug and nitroxide fullerene derivative resulted in the survival of 70% animals, classifying these compounds as promising modifiers of biological reaction for tumor therapy. 

The first carbon nanostructure that was covalently modified to alter surface properties was the C60 fullerene. After its discovery in the mid-1980s, numerous functionalization methods were developed for obtaining two important classes of derivatives, methanofullerenes and fullerene Diels-Alder adducts. 

Diazo compounds also undergo cycloaddition with fullerenes [for reviews, see (104),(105)]. These reactions are HOMO(dipole)-LUMO(fullerene) controlled. The initial A -pyrazoline 42 can only be isolated from the reaction of diazomethane with [60]fullerene (106) (Scheme 8.12) or higher substituted derivatives of Ceo (107). Loss of N2 from the thermally labile 42 resulted in the formation of the 6,5-open 1,2-methanofullerene (43) (106). On the other hand, photolysis produced a 4 3 mixture of 43 and the 6,6-closed methanofullerene (44) (108). The three isomeric pyrazolines obtained from the reaction of [70]fullerene and diazomethane behaved analogously (109). With all other diazo compounds so far explored, no pyrazoline ring was isolated and instead the methanofullerenes were obtained directly. As a typical example, the reaction of Cgo with ethyl diazoacetate yielded a mixture of two 6,5-open diastereoisomers 45 and 46 as well as the 6,6-closed adduct 47 (110). In contrast to the parent compound 43, the ester-substituted structures 45 and 46, which are formed under kinetic control, could be thermally isomerized into 47. The fomation of multiple CPh2 adducts from the reaction of Ceo and diazodiphenylmethane was also observed (111). The mechanistic pathway that involves the extrusion of N2 from pyrazolino-fused [60]fullerenes has been investigated using theoretical methods (112). 

For methanofullerenes, the triplet-triplet absorption appears arround 720 nm, for cyclohexylfused derivatives, pyrrolidino- and dihydro-fullerene, the absorption appears arround 700 nm [62,71,72]. 

Finally, the wide applicability and the experimental simplicity of the retro-Bingel reaction was evidenced in the isolation of pure enantiomers of C76, in the formation of methanofullerene compounds not accessible otherwise, such as ( )-75, and in the separation of constitutional isomers as well as of enantiomers of Cg4. The retro-cyclopropanation reaction seems to be generally selective, and still needs to be exploited in the preparation of unusual derivatives with controlled regiochemistry. 

In a bulk-heterojunction photovoltaic cell with methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) as an electron acceptor, alternating copolymer 19 (Fig. 9), derived from 2,7-fluorene and 2,5-dithienylsilole, can show impressive performance as the electron donor.31 In a device configuration of ITO/PEDOT/active layer/Ba/Al, the dark current density—bias curve shows a small leakage current, suggesting a continuous, pinhole-free active layer in the device. Under illumination of an AM 1.5 solar simulator at 100 mW/cm2, a high short-circuit current of 5.4 mA/cm2, an open-circuit voltage of 0.7 V, and a fill factor of 31.5% are achieved. The calculated energy conversion efficiency is 2.01%. 

There has been one derivative ofbis(methanofullerene) carrying two dendritic wedges (Fig. 71) fhaf was claimed to show a mesophase between 40 and 70 °C, though the phase was not identified the precursor itself displayed a nematic phase (Cr 48 N 63 I) [305]. 

Fulleropyrrolidines constitute an important family of Ceo derivatives that have the advantage over the methanofullerene systems in that they lead to stable reduced species, allowing the development of fullerene-based redox molecular switches. In order to promote mesomorphism in such a mono-adduct structure, Deschenairx et al. decided to modify the Ceo derivative by the use... 

Three new phosphonate derivatives of Cgo methanofullerenes (499), (500) and (501) were synthesized. Their electrochemical behavior and the pathways involved in the retrocyclopropanation reactions were also investigated (Figure 96). ... 

The need to prepare fullerene derivatives for possible applications to medicine and material sciences resulted in the development of novel synthetic methods for the functionalization of Cso. R. Pellicciari et al. reacted Ceo with carboalkoxycarbenoids generated by the Rh2(OAc)4-catalyzed decomposition of a-diazoester precursors. This reaction was the first example of a transition metal carbenoid reacting with a fullerene and the observed yields and product ratios were better than those obtained by previously reported methods. The reaction conditions were mild and the specificity was high for the synthesis of carboalkoxy-substituted[6,6]-methanofullerenes. When the same reaction was carried out thermally, the rearranged product (the [6,5]-open fullerene) was the major product. 

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