Functionalization of fullerenes

Because the reaction occurred in solution and, in these early days, in an effort to avoid explosion hazards [18], a modified domestic microwave oven was used. By use of microwave irradiation higher yields of the desired products were obtained more quickly (39% yield after irradiation for 20 min) than under thermal condi- 

Application of microwave irradiation in conjunction with use of toluene as solvent gave cycloadduct 5 in 35% yield after 15 min at 800 W [20], an improvement on the yields obtained by conventional heating. This higher yield is probably because of reduced reversion of the cycloaddition in the shorter period of time needed for the irradiated reaction. It is remarkable that under microwave conditions the formation of bis adducts was not observed in these reactions. 

Hetero-Diels-Alder Reactions The hetero-Diels-Alder reaction is one of the most important methods for the synthesis of heterocyclic compounds. Although it is a potentially powerful synthetic tool it has, however, been used relatively seldom. 

Microwave irradiation has been used to improve reactions involving heterodieno-philes and heterodienes of low reactivity. 

Addition of a 1,3-dipole to an alkene to give a five-membered ring is a classical organic reaction. Indeed, 1,3-dipolar cycloaddition reactions are useful for formation of carbon-carbon bonds and for preparation of heterocyclic compounds. 

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Keywords Diels-Alder reaction of exohedral functionalization of fullerenes and preparation of heterocyclic fullerenes... 

ThUgen C, Sergeyev S, Diederich F (2004) Spacer-Controlled Multiple Functionalization of Fullerenes. 248 1-61... 

Eguchi and Ohno have used silyl nitronate induced 1,3-dipolar cycloaddition for functionalization of fullerene C60 (Eq. 8.76).127a Nitrile oxides also undergo 1,3-dipolar cycloaddition... 

Maggini, M., and Scorrano, G. (1993) Addition of azomethine ylides to CM Synthesis, characterization, and functionalization of fullerene pyrrolidines./. Am. Chem. Soc. 115, 9798-9799. 

Scheme 6.197 Functionalization of fullerene and single-wall carbon nanotubes through cycloaddition chemistry.

Fullerenes Cycloaddition reactions are very popular for functionalization of fullerenes. Such reactions of fullerenes are compiled and discussed in detail in Reference 253. During the last 10 to 15 years, several communications appeared concerning [3 + 2] cycloaddition of nitrile oxides to fullerene C60- Nitrile oxides, generated in the presence of C60, form products of 1,3-cycloaddition, fullerene isoxazolines, for example, 89. The products were isolated by gel permeation chromatography and appear by and 13 C NMR spectroscopy to be single isomers. Yields of purified products are ca 30%. On the basis of 13C NMR, structures with Cs symmetry are proposed. These products result from addition of the nitrile oxide across a 6,6 ring fusion (254). 

F. Diederich, R. Kessinger, Regio- and Stereoselective Multiple Functionalization of Fullerenes in Templated Organic Synthesis , Eds. P. J. Stang, F. Diederich, Wiley-VCH, Weinheim, 1999, pp. 189-218. 

Tabata Y, Ikada Y (1999) Biological functions of fullerene. Pure Appl Chem. 71 2047-2053. 

Covalent functionalization of fullerenes has also been used to obtain surface-modified fullerenes that are more compatible to polymer matrices in order to fabricate composites. In this context, four basic strategies were developed. The first one allows the fullerenes to react during the monomer polymerization, so that the fullerene can be attached to the polymer chain [111, 112]. Second, an already synthesized polymer is treated using specific conditions that allow the chemical reaction with fullerenes [113,114]. Third, the fullerenes are chemically bonded to a monomer which is polymerized or co-polymerized to obtain the modified monomer [115,116]. Fourth, a dendrimer can be synthesized around a fullerene which then acts as a nucleus [117,118]. 

Although there have been great advances in covalent functionalization of fullerenes to obtain surface-modified fullerene derivatives or fullerene polymers, the application of these compounds in composites still remains unexplored, basically because of the low availability of these compounds [132]. However, until now, modified fullerene derivatives have been used to prepare composites with different polymers, including acrylic [133,134] or vinyl polymers [135], polystyrene [136], polyethylene [137], and polyimide [138,139], amongst others. These composite materials have found applications especially in the field of optoelectronics [140] in which the most important applications of the fullerene-polymer composites have been in the field of photovoltaic and optical-limiting materials [141]. The methods to covalently functionalize fullerenes and their application for composites or hybrid materials are very well established and they have set the foundations that later were applied to the covalent functionalization of other carbon nanostructures including CNTs and graphene. 

Abstract More than a decade has passed since fullerenes became avaUahle to researchers in almost all fields of science. The explosive development of study on the chemical functionalization of fullerenes has led to a wide variety of fullerene derivatives. However, most of these reactions have been carried out in the liquid phase, and curiously enough the solid-state reaction (or solid-solid reaction) of fullerenes has been developed only in recent years. This chapter focuses on the solid-state reaction of fullerenes, particularly the reaction which was conducted under what is called high-speed vibration milling conditions. It will be shown how this reaction technique is pertinent for the creation of fullerene derivatives with novel structures, and how efficient this method is for certain reactions compared with the liquid-phase reaction. 

Research Focus Functionalization of fullerene molecule with perfluorosulfonic acid for use as a Nafion -like fuel cell electrode. 

Secondary Functionalization of Fullerene Monoadducts by Cycloaddition Reactions... 

Besides the 1,3-dipolar cycloaddition of azomethine ylides to C60, the Bingel cycloprop anation reaction is widely used for regioselective functionalization of fullerenes. In principle, this versatile modification involves the generation of carbon nucleophiles from a-halo esters and their subsequent addition to C60 [19]. The addition takes place exclusively on double bonds between two six-membered rings of the fullerene skeleton, yielding methanofullerenes. As shown in Scheme 2, addition of diethylbromomalonate to C60, in the presence of an auxiliary base... 

Recently photorefractivity in polymers has been demonstrated [137,138]. The second-order nonlinearity is obtained by poling the polymer doped with a nonlinear chromophore. Such a polymer may or may not be a good photoconductor. Usually sensitizers have to be added to enhance the charge-generation efficiency. Semiconductor nanoclusters represent a new class of sensitizing material for this purpose. The sensitizer function of fullerene in a photorefractive polymer has been demonstrated recently [138]. 

Regio- and Stereoselec tive Multiple Functionalization of Fullerenes... 

The functionalization of fullerenes is predominantly through addition reactions [70]. With many double bonds in a fullerene molecule (30 for Cgo), multiple additions to the same fiillerene cage are quite common in fullerene derivatization. For Cgo derivatives, there is a suggestion that the monoadducts... 

Figure 18. Heat of formation of carbon fullerenes relative to that of graphite as a function of fullerene size obtained from the TBMD calculations. (From Ref. 76.)...

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