Fullerenes methano

Diederich F, Jonas U, Gramlich V, Herrmann A, Ringsdorf H and Thilgen C 1993 Synthesis of a fullerene derivative of benzo[18]crown-6 by Diels-Alder reaction complexation ability, amphiphilic properties, and x-ray crystal structure of a dimethoxy-1,9-(methano[1, 2]benzomethano)fullerene[60] benzene clathrate Helv. Chim. Acta 76 2445-53... 

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. 

Methanesulfonyl chloride, 23 653, 681-683 Methano[60]fullerenes, 12 242 Methanogenic conditions, defined, 3 757t Methanoic acid, physical properties, 5 29t Methanol, 16 299-316. See also Methanol synthesis... 

As well as the Bingel reaction and its modifications some more reactions that involve the addition-elimination mechanism have been discovered. 1,2-Methano-[60]fullerenes are obtainable in good yields by reaction with phosphorus- [44] or sulfur-ylides [45,46] or by fluorine-ion-mediated reaction with silylated nucleophiles [47]. The reaction with ylides requires stabilized sulfur or phosphorus ylides (Scheme 3.9). As well as representing a new route to l,2-methano[60]fullerenes, the synthesis of methanofullerenes with a formyl group at the bridgehead-carbon is possible. This formyl-group can be easily transformed into imines with various aromatic amines. 

The reverse reaction to the Bingel cyclopropanation - the so-called retro-Bingel reaction - was developed by Diederich, Echegoyen and coworkers [70] and opens up the possibility to remove the Bingel-addend completely. This removal was successfully done with Cjq malonates [70, 71], dialkoxyphosphorylmethano[60]-fullerene [72], methano[60]fullerenyl amino acid derivatives [73] and also with... 

Figure 4.6 Chemical shifts for the bridgehead C atoms and the methylene H-atoms and coupling constants j(CH) for the methano bridge C atoms in H2 for isomers 113a and 113b. The corresponding C atoms resonate in the region between 130 and 150 ppm together with all other sp -carbons of the fullerene sphere. For the 1,6-addition adduct of with (p-methoxy-phenyl)diazomethane, the peak position of the bridgehead C atoms was found by HETCOR analysis to be 138.65 ppm [110. ...

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. 

Thermal extrusion of N2 from O-benzyl- and O-pivaloyl-protected diazirine yields the corresponding carbenes, which react with in toluene to give the fullerene sugars 333 (Scheme 4.67) [377, 378]. These [2+1] carbene additions cleanly lead to 1,2-methano-bridged sugar monoadducts. 

Reactions of Cjq with metal carbene complexes also yield the [6,6] methano-fullerenes [392]. These adducts are probably not formed via a carbene addition, but via a formal [2-1-2] cycloaddition under formation of a metalla cyclobutane intermediate. The Fischer carbene complex [mefhyl(methoxymethylene)]pentacarbonyl chromium can be utilized to prepare l,2-mefhyl(methoxymethano)-fullerene in 20% yield [392]. A tungsten carbene complex was primarily used to initiate the formation of a polyacetylene polymer, but it was discovered that addition of to the complex-polymer-mixture improves the polymerization and dramatically increases the catalytic activity of the carbene complex [393]. can be integrated into the polymer via carbene addition. 

Formation of cluster opened methano- and imino[60[fullerenes (fulleroids and azafUlleroids) Thermal [3+2]-cycloadditions ofdiazo compounds or azides leads to the formation of fulleropyrazolines or fullerotriazolines. Thermolysis of such adducts after extrusion of N2 affords as kinetic products the corresponding [5,6]-bridged methano and iminofullerenes with an intact 60 re-electron system and an open transannular bond (see Chapter 4) [88-91]. The corresponding [6,6]-bridged structures with 58 re-electrons and a closed transannular bond are formed only in traces. 

The removal of methano addends from fuUerenes using CPE is an efficient and versatile procedure, which has heen successfully employed in the separation of enantiomers and constitutional isomers of the higher fullerenes, for the isomerization of his- and tris-adducts of Ceo, and more recently, for the selective removal of one addend in the presence of another. 

These studies were initiated upon observing that the ds-2-bis-methano-fullerene, (57), was the only one of six bis isomers available synthetically (see Fig. 23) that exhibited an irreversible second reduction wave by CV and SSV [105]. A one-electron CPE of (57) in DCM atthe first reduction potential followed by reoxidation... 

The usefulness of the retro-cyclopropanation reaction is even more remarkable than previously anticipated. It was questioned whether this reaction allowed the selective removal of a Bingel-type addend while leaving addends of a different type unaffected. A variety of mixed bis-adducts such as those shown in Fig. 29, were prepared, all of which contained a bis(ethoxycarbonyl)methano group [182]. In all cases, CPE led to the selective removal of the Bingel addend in over 60% yield, while the other one was retained, confirming that the reaction may be used in a synthetic protection-deprotection protocol to prepare novel fullerene derivatives. 

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. 

Figure 3 Comparison of absorption and fluorescence (inset) spectra of different classes of C6oderivatives themethano-C6oderivative l -carboxy-l,2-methano[60]fullerene the pyrrolidino-C6o derivative N-ethyl-trans-2, 5 -dimethylpyrrolidino[3, 4 l,2][60] fullerene 33 (Fig. 24) (- - -),[B14al the C60 derivative 2-hydroxy-tetrahydrofu-ran[4, 5 l,2] [60]fullerene (—), and the amino-C60 derivative 3 (Fig. 4) AW -dimethyl-piperazine [2, 3 l,2][60]fullerene (-). (From Ref. 65.)...

UV-vis spectroscopy and NMR investigations clearly demonstrate that isomer 59b is the 6,6-adduct of C6o with C2v symmetry, namely the methano fullerene. There is crucial evidence supported by H and 13C NMR for the isomer 59a being the 5,6-adduct of C6o with Cs symmetry. No isomerization of the pure fulleroid to the methanofullerene or vice versa upon photolysis is observed as reported by Wudl et al. [238], Thus, the isomeric ratio of the two isomers reveals the formation ratio of carbene and diazo compound during the reaction. 

The thermal Diels-Alder reaction ([4 + 2] cycloaddition) is widespread in the synthesis of fullerene derivatives. In contrast, only a few examples of the photochemical Diels-Alder reaction in solution or in the solid state are known. The first example is described by Tomioka and coworkers [249], Irradiation of ketone 73 and C6o at 10°C with a high pressure mercury lamp through a Pyrex filter led to the formation of 61-hydroxy-61-phenyl-l,9-(methano[l,2]benzenomethano) fullerene 75 (Scheme 29). This compound is unusually unstable and yields the monoalky 1-1,2-dihydrofullerene 76 either by silica gel chromatography or upon heating. 

At the beginning of this chapter, we mentioned how the removal of di(alkoxycar-bonyljmethano addends on a C6o core can be achieved by electrolytic reduction to yield the parent [60]fullerene. This so-called retro-Bingel reaction was initially conducted on diethyl l,2-methano[60]fullerene-61,61-dicarboxylate (see Figure 1) leading to > 80 % yield of recovered C60 after controlled potential... 

In another example, diazo compounds cycloadd to fullerenes across a 6,6 double bond to give fulleropyrrazolines, that decompose to mixtures of methano-fullerenes and methanofulleroids either thermally or photochemically [82]. 

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