Fullerenes azide addition

Beside the fact that azide addition to C50 is a convenient method for functionalizing fullerenes, the iminofullerenes also serve as precursors in the synthesis of nitrogen heterofullerenes [171]. Their chemistry is described in more detail in Chapter 12. 

Several groups have noted similar findings for azide addition, in which the structure of the bisadduct depends on the nature of the starting alkyl azide or bisazide [39-41]. Even chiral bisazafulleroids have been prepared [42,43]. As an interesting example, it was found that subsequent addition of azido ester to N-ethoxycarbonyl-azirenofullerene resulted in the formation of bisadduct 12 and not 11 [40]. Structure 12 constitutes the first fullerene derivative having [6,... 

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]. 

In a different approach to aza[70]fullerenes by Hirsch and coworkers, twofold azide addition yielded Cj-symmetrical 31 which results from bridging two adjacent 6-5 open bonds and is a suitable starting material for the macroscopic synthesis of the Cj-symmetrical 2,2 -diaza-l,l -bi([70]fullerenyl) 29 [116] (Scheme 2) formed together with the monomeric l-[2-(methoxy)ethoxy] -IH-2-aza[70]fullerene [117] (not shown). The latter probably results from trapping of C59N+ intermediates by the acetal cleavage product 2-methoxyethanol. Aza-fullerene formation occurs through elimination of one C-atom (presumably... 

Several studies have demonstrated the successful incoriDoration of [60]fullerene into polymeric stmctures by following two general concepts (i) in-chain addition, so called pearl necklace type polymers or (ii) on-chain addition pendant polymers. Pendant copolymers emerge predominantly from the controlled mono- and multiple functionalization of the fullerene core with different amine-, azide-, ethylene propylene terjDolymer, polystyrene, poly(oxyethylene) and poly(oxypropylene) precursors [63,64,65,66,62 and 66]. On the other hand, (-CggPd-) polymers of the pearl necklace type were fonned via the periodic linkage of [60]fullerene and Pd monomer units after their initial reaction with thep-xy y ene diradical [69,70 and 71]. 

Diazabishomofullerenes with another addition pattern can only be obtained in good yields if a tether directed synthesis is applied. If the tether between two azide groups is sufficiently rigid a second addition is forced to occur at specific regions of the fullerene cage [36, 37]. 

Systematic investigations of twofold additions of malonates to C70 revealed that the second addition takes place at one of the five a-bonds of the unfunctionalized pole [17, 26], With achiral, C2v-symmerical malonate addends, three constitutionally isomeric bisadducts are formed An achiral one (C2v-symmetrical 1), and two chiral ones (C2-symmetrical 2 and 3), which are obtained as pairs of enantiomers with an inherently chiral addition pattern (Figure 13.5). Twofold addition of chiral malonates leads to the formation of five optically active isomers, two constitutionally isomeric pairs of C2-symmetrical diastereomers and a third constitutional C2-symmetrical isomer (Figure 13.5). Twofold additions of azides to C70 lead to diazabis[70]homo-fullerenes, which served as starting material for the synthesis of bis-(aza[70]-fullerenyl) (Cg9N)2 (Chapter 12) [27]. As further bisadditions, addition reaction to C70 [2+2]cycloaddition of electron-rich bis(diethylamino)ethyne and 1-alkylthio-2-(diethylamino)ethynes [28] and the addition of transition metal fragments have been reported [29-32],... 

Banks et al. reported the formation of the expected [6,6]-closed aziridino-fullerene by the reaction of C6o and singlet oxycarbonylnitrenes [271], In addition, small amounts of unexpected closed [5,6]-closed adducts were postulated [272], In further investigations, Banks et al. studied the irradiation of C6o and ethyl azid-oformate 109 in benzene leading to a 4 1 mixture of two major products (Scheme... 

Other tethers have been employed in the search for regioselectivity in multiple additions to fullerenes. Some of these methodologies include the use of bis(o-quinodimethanes) connected by a, oo-dioxamethylene tethers [40], tethered nucleophilic vinylcarbenes [41] or azides [42],... 

It is known [1, 11], that the addition of organic azides leads to the formation of 5,6-open monoorganofullerenes (monoazahomofullerenes). Moreover, it is shown, that in contrast to the reactions of 6,6-closed monoorganofullerenes with azides, the cycloaddition of azides to azahomofullerenes can result to the formation of one bis(organo)fullerenes isomer as the predominate product [12]. However, the question is whether regioselective cycloaddition of azide to monoazahomofullerenes depends on the structure of azide organic fragment. The present communication is devoted to the search of the answer to this question, because a little amount of isolated communications did not answer the question [13-17]. 

Scheme 1.24. Regioselective addition to Cgo of a 2,3-O-isopropylidene-L-threitol-tethered bis-azide under formation of diaza-bishomo-[60]fullerene 252, and regioselective interconversion between the azahomo- (252) and the epiminofullerene (254) isomers.

The same approach was used to add five additional PS or PI chains on a monoadduct PS-Cbo prepared by reacting the fullerene with an azide-terminated polystyrene (Scheme 5.13) [74]. 

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