Fullerene mono adduct

Addition reactions — The fullerenes Ceo and C70 react as electron-poor olefins with fairly localized double bonds. Addition occurs preferentially at a double bond common to two annelated 6-membered rings (a 6 6 bond) and a second addition, when it occurs is generally in the opposite hemisphere. The first characteriz-able mono adduct was [C6oOs04(NC5H4Bu )2]. formed by reacting Cgo with an excess of OSO4 in 4-butylpyridine. The structure is shown in... 

The cytotoxic and photocytotoxic effects of two water-soluble fullerene derivatives, a dendritic CL mono-adduct and the malonic acid CL tris-adduct were tested on Jurkat cells when irradiated with UVA or UVB light (Rancan et al., 2002). The cell death was mainly caused by membrane damage and it was UV dose-dependent. Tris-malonic acid fullerene was found to be more phototoxic than the dendritic derivative. This result is in contrast to the singlet oxygen quantum yields determined for the two compounds. 

Preparation of mono-adducts of fullerene - for studies on electrostatic interactions - was undertaken by cyclopropanation of fullerene with appropriately functionalised malonic esters 1 (Bingel reaction) to form 2. Coupling with the tert-butyl protected oligoamide-amino-dendron 3 and subsequent hydrolysis lead to the water-soluble fullerene dendron 5, which can carry up to nine negative charges after depro to nation. After association with the zinc complex of cytochrome C, photoinduced electron transfer (PET) from the redox protein to the fullerene can be accomplished, which was studied by fluorescence spectroscopy. 

Following our protocol to separate fullerene isomers by the intermediacy of defined covalent adducts, the fraction of fullerene soot was subjected to Bingel cyclopropanation with bis (.S )-l -phenyl butyl malonate (cf. Section III.C).60 Among the products two chiral mono-adducts and four chiral bis-adducts were isolated in pure state and characterized. An analysis taking into consideration the symmetries of the compounds as deduced from H- or 13 C NMR spectroscopy, the magnitudes of their Cotton effects (these are relatively large, between ca. 10 and 200 M 1 cm-1 in the case of chiral fullerene... 

Scheme 1.26. Formation of the D2-symmetric bis-adduct 133 of Di -Cu from C2-symmetric mono-adduct 132 and generation of the parent fullerene by electrochemical retro-Bingel reaction.

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... 

Hirsch and co-workers subsequently discovered that the yield of hexakis-adducts such as 8 or 9 can be greatly increased and their separation from side products substantially facilitated, if 9,10-dimethylanthracene (DMA) is used as a template (Scheme 7-2) [14, 15]. Anthracene derivatives such as DMA are well known to undergo reversible Diels-Alder additions with fullerenes at ambient temperamre [16-18]. After addition to the fullerene, the template directs diethyl malonate addends in the Bingel addition tegio-selectively into e positions, ultimately yielding the hexakis-adducts with a pseudo-octahedral, all-e addition pattern. The templated activation of e 6-6 bonds (bonds between two six-membered rings) is also efficient starting from C o mono-adducts, and several examples are shown in Scheme 7-2. Thus, bis(alkynyl)methanofullerene 10 [19] reacted with diethyl 2-bromomalonate/DBU (8 equiv) and DMA (12 equiv) to provide hexakis-... 

Chung s research group recently reported a different type of sultine-type precursor [70], The synthesis of heterocyclic sultines 63 has been reported elsewhere [71]. Conventional heating of 2,5-disubstituted thienosultines 63 with [60]fullerene 59 in o-DCB under reflux for 2-24 h produces the biradical intermediates 64 which are subsequently trapped by [60]fullerene 59 to produce the cycloadducts 65 and bis adducts 66 in 37-79% yields in 2 1 to 3 1 ratios (Scheme 11.19). The reaction was highly accelerated under microwave conditions (900 W, <180 °C) for only 4 min. The ratio of mono adducts 65 to bis adducts 66 was also increased from 2-3 1 to 3.5-6 1 when microwaves were applied [18]. 

In order to evaluate the influence of the geometric and electronic properties of the educts on the observed product distributions a variety of experimental and calculated mono adduct structures were analyzed (Fig. 21, Table 5). For example, as can be seen from the X-ray crystal structure of 47 the average values of the [5,6] -bonds are 1.451 A and those of the [6,6] -bonds excluding the cyclo-propanated [6,6]-bond between C-1 and C-2 1.388 A [102]. This clearly shows that the [5]radialene-type structure of the fullerene cage is preserved. 

In the case of the second most favored C(5)-C(6)-adduct (type P) which often accompanies the C(l)-C(2) mono-adduct in product mixtures [27], a f 2v -symmetrical addend again affords a single product isomer (e.g. 7-10, Fig. 5), whereas addition of a Q-symmetrical addend leads to a pair of enantiomers [( )-ll. Fig. 5]. In the latter case, a chiral addition pattern is created on the fullerene spheroid. Being due only to differences in nature, sequence, or steric arrange-... 

All C(7)-C(21) adducts of C70 are Q-symmetrical and interesting from a stereochemical viewpoint because they are the only 6-6 bond mono-adducts of this fullerene with an inherenly chiral functionalization pattern [34]. The bond in question, however, is not among the types a-y (Fig. 4) and has a relatively low local curvature [14]. Furthermore, its reactivity is probably reduced by its location in a six-membered ring with a relatively high benzenoid character [ 121 ] (cf. Sect. 4.1.5 and Fig. 6). Despite its high frequency (20 bonds vs. 10 bonds of type a and 10 bonds of type J3 in C70), the low reactivity may therefore account for the few observations of C(7)-C(21) adducts. 

In the case of achiral, C2v-symmetrical malonate addends, three constitutionally isomeric bis(methano)fullerenes are formed [54,131 ] An achiral one ( 2 -symmetrical 45), and two chiral ones (C2-symmetrical ( )-46 and ( )-47) which are obtained as pairs of enantiomers with an inherently chiral addition pattern [54] (Fig. 7). The tree constitutional isomers are formed in the approximate ratio 2.8 6.2 1 which differs substantially from the statistical 1 2 2 ratio and shows a marked preference for the second addition taking place at bonds C(56)-C(57)/C(59)-C(60) as compared to C(67)-C(68)/C(69)-C(70) (for the numbering of C70, cf. Fig. 3). Electroiuc factors such as the coefficients of the LUMO of the mono-adduct, to which the electron density of the incoming nucleophile is transferred [95], may explain the observed selectivity among distant bonds of (nearly) identical local curvature. 

Amines can add to C50. An early paper showed that up to 15 amine molecules may be added to the fullerene, but the hexa-adduct with the chains attached to the central double bond of the six pyracyclene unit constituting the Qo seems favored [32]. This addition has been used to graft Qo on poly(ethylene imine) and poly(4- [(2-aminoethyl)imino]methyl styrene) [33] or amine functionalized ethylene propylene terpolymer [34] to obtain sidefullerene polymers. Amino-terminated polystyrene with very narrow molar mass distributions, synthesized using amonic polymerization followed by end functionalization, can add to Coo to form multiarm stars (Scheme 5.7). Even, if a ratio C60/PS-NH2 of 2 1 is used in order to favor the mono-adduct, about 20% of di-adducts as well as small amounts of higher adducts are obtained [35]. 

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