Bridged fullerenes

Isaacs, L., Wehrsig, A., and Diederich, F. (1993) Improved purification of C60 and formation of S- and 7i-homoaromatic methano-bridged fullerenes by reaction with alkyl diazoacetates. Helv. Chim. Acta 76, 1231-1250. 

Figure 4.7 Electronic-absorption spectra recorded in toluene of a mixture of (ethoxycarbonyl)-methylene-bridged fullerenes 114 with the relative ratio (1 1 3) (—), of pure isomer 114a (- ), and of Qq (—) [129. ...

An enantiopure dimer 149 with a l,l -binaphthyl-bridge was prepared via the bis-tosylhydrazone (see Table 4.4, page 130/131) [122], The electronic properties of these dimers, such as the electronic absorphon spectra and cyclic voltammetry, are indistinguishable from those of other methano-bridged fullerenes. CV-data show clearly that the two CgQ-imits of the binaphthyl-dimer are reduced independently [122],... 

The synthesis of a diphenylmethano-bridged fuUerene derivahve with reactive functional groups on the phenyl rings is exemplified by the preparahon of the diphenol derivative 118 (Scheme 4.23). It can be obtained from the corresponding methyl ether by treatment with BBrj in o-dichlorobenzene at 0 °C to room temperature in 94% yield. In contrast to the non-polar diphenyl-methano bridged fullerenes, 118 is soluble and stable in pyridine but sparingly soluble in benzene or toluene. 

The synthesis of a water-soluble diphenylmethano-bridged fullerene 122 was achieved by hydrolyzing the bis (acetamide) 121 with acetic acid-aqueous hydrochloric acid and then converting it into the bis(succinamide) 122 by treatment with succinic anhydride (Scheme 4.25) [158]. Compound 122 is soluble in water at pH > 7. This is an important requirement for the investigation of the biological activity of fullerenes. Remarkably, 122 is an inhibitor for the HIV enzymes protease (HIV-P) and reverse transcriptase (HIV-RT) [159]. As suggested by molecular modeling. 

The possible opening and closure of transannular cis-1 bonds in bisimino-bridged fullerenes such as 6 and 7 is governed by the following factors [17, 18] ... 

A broad variety of methano-bridged fullerenes are accessible by the reaction of Cgo with different diazomethanes. This chemical transformation of Cgo was discovered by Wudl and is based on the findings that Cgo behaves as an 1,3-dipolarphile3. 

Wooley et al.1511 have described the creation of fullerene-bound dendrimers (Scheme 5.14). Reaction of C60 with bis(p-methoxyphenyl)diazomethane 54 and subsequent cleavage of the methyl ethers afforded a 6-6 methano-bridged fullerene (55) possessing two phenolic moieties, as the major product.1521 Treatment of the bisphenolic fullerene 55 with 2.7 equivalents of the activated dendron (52) afforded the desired substituted fullerene (56) possessing two dendritic arms. 

Another improvement of the DPM rigidity and preorganization without alteration of the substitution pattern is the back-stabilization of the gable conformation. The 1.1-diphenylcyclopropane derivatives invariably show preference for the gable conformation, as revealed from x-ray data. Also, in diarylmethane-bridged fullerenes, the gable disposition was described as the most stable conformation. However, no experimental rotational barriers were reported until now. 

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