Fulleroid derivatives

The same characteristic patterns in H chemical shifts are found in fulleroid derivatives such as 23— 28 or 29—33,2 ° 2i7 where either a proton or a methyl group is placed above a fullerene ring (Figure 15). In the case of the methyl groups, the effects appear to be somewhat attenuated (for Instance, Ad between 30 and 31 is only 1.9 ppm), certainly due to the averaging of the three methyl protons, only one of which will be located in close proximity to the ring at a given time. 

The same type of methanofullerene and fulleroid derivatives as for Ceo can be observed for C70. For derivatives of the latter, several isomers are possible, some of which have been observed and characterized,namely, the cyclopropane derivatives 34 and 35 and the fulleroids 36 and 37 (Figure 16).The <3( H) values of the polar adduct 36 are very similar to those of the corresponding Ceo derivative, 19 (Figure 15). The same is true for the low-frequency... 

Similarly, irradiation of tetrasubstituted bis(fulleroid) derivatives 72 in the presence of oxygen affords a 12-membered ring diketone on the surface of the fullerene. In spite of the same 60 n electronic structure as C o, whose photooxygenation leads to the formation of the fullerene epoxide, [2 -I- 2]-cycloaddition of 72 with Oj followed by symmetrical ring opening of the dioxetane 73 predominantly occured to give 74 (Scheme On the contrary, oxidation and Diels-Alder reaction of the mother... 

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]. 

All 7-fiilleroids known so far and simple ways to describe them are given in Section 19.1 based on that some infinite series are introduced. In Section 19.2, a necessary condition for the p-vectors, which implies that five of the new 7-fulleroids are minimal for their respective values of v, is derived. 

ESI-MS of fulleroid 1,2-oxazetidine 34 (Equation 2), obtained by a hetero-Diels-Alder reaction between buck-minsterfullerene Cgo and nitrosobenzene, provided a useful method for the characterization of small neutral organic molecules, otherwise not detectable, as fullerene derivatives <1997USP5635404>. 

In contrast to the N-MEM (N-alkyl) analogue (see Sect. 2.2.2), N-aryl-aza-fiilleroids, obtained from the thermal reaction of aryl azides with 50, can be photochemically isomerized to azirenofullerenes [51]. This closely resembles the difference in the photochemical behavior of C-aryl- and C-alkyl fulleroids obtained from the reaction of diazo compounds with Qo (e.g. [5,6] CgiHj is photochemically stable). After some initial studies (see for example [52-55]), the addition of azides and nitrenes to C o has been investigated and used for the preparation of a series of functional fullerene derivatives by a number of other investigators, but their work is not relevant in relation to the preparation of aza[60] fullerene. The addition of azides to fullerenes has been brie% reviewed previously [56-58]. 

Nuber and Hirsch, in the meantime, prepared bisaza[70]fulleroid 60 in a one-step synthesis from C70 with MEM azide in ODCB at 120°C. They observed that while 60 was formed preferentially, another bisadduct isomer [presumably the (l,6) (l,9)-isomer, according to modern lUPAC numbering] was formed as a byproduct. When this material was subjected to the reaction conditions that afforded aza[60]fullerenes from 8 (see Sect. 2.2.5), an analogous aza[70]fullerene dimer, most likely with the structure 61, and the methoxyethoxy derivative 62 could be isolated from the mixture in 10 and 15% yield, respectively (Fig. 26)... 

Fluorescence quantum yields of the C o derivatives were quantitatively determined. For the mono-functionalized Cgo derivatives, the compound with a (5-6)-open fulleroid addition pattern on the fullerene cage appeared to be considerably less fluorescent than those with a [6,6]-closed cage addition pattern. Despite the disturbance of the electronic structure via multiple additions to the fullerene cage, the multiple-functionalized Cgo derivatives exhibited no dramatic changes in fluorescence quantum yields in... 

Recently, the electrochemistry of fullerenes and their derivatives has gained much attention [33]. Cgo, C70 and higher fullerenes were reduced electrochemi-cally, and six reduction waves were observed for both Cgo and C70 [34], as well as for most of the higher fullerenes [35]. The energy levels that were obtained from these experiments were mostly in line with MO calculations. The electrochemistry of numerous fullerene derivatives was studied to compare their electron affinities and energy levels with their parent fullerenes. Electrochemically induced isomer-izations can be observed in CV, as is the case in the rearrangement of fulleroids to methanofullerenes [36]. 

Compared to Ceo and C70, the chemistry of the higher fullerenes is still in its infancy and is essentially restricted to reduction and addition reactions of the most abundant isomers of C76, C78, and Cyclopropanation has emerged as a versatile means of derivatization, but no fulleroid-type derivatives have been reported so far. Even if these could be isolated eventually, assignment of the plethora of possible regioisomers will be extremely difficult. Thus, exohedral NMR probes will, at least in the near future, be of limited use for the study of ring currents in the higher fullerenes. 

Inoue, H., Yamaguchi, H., Iwamatsu, S.-L, Uozaki, T., Suzuki, T., Akasaka, X, Nagase, S., and Mutata, S., Photooxygenative partial ring cleavage of bis(fulleroid) synthesis of a novel fullerene derivative with a 12-membered ring, Tetrahedron Lett., 42, 895, 2001. 

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