Methanofullerene Materials

The novelty of this type of organic functionalization is explained in terms of the wide number of different methanofullerene materials that can be reached due to the presence of esters moieties either properly functionalized carbon nucleophiles can be constructed that ultimately would add to C60, or additional chemical transformation to the addend group of an already synthesized methanofullerene could occur. Thus, theoretically, any chemical group carrying novel physical, electronic, magnetic, or mechanical properties that fulfills the appropriate requirements for the construction of novel organofullerene hybrid materials can be properly designed and, thus, attached on the fullerene skeleton. 

An important field where the cyclopropanation reaction finds growing application is the construction of dendrimers possessing fullerenes either as functional cores [26-33] or branches [34-38]. Dendrimers can serve as building blocks for the construction of organized materials with nanosize precision due to the well-defined three-dimensional structure they possess. An issue of great importance is to incorporate photoactive and/or redox-active units at the center of the dendrimer in order to establish these types of materials as molecular devices. An example of an organofullerene material that has the potential to serve as a core building block for the construction of dendrimeric compounds 

Several cyclopropanated organofullerene materials have been synthesized for the preparation of fullerene-containing thermotropic liquid crystals. A wide variety of such liquid-crystalline materials were synthesized possessing mono-140-42], hexa-addition [43] pattern, or even dendritic addends [44-46]. 

Cyclobutanefullerenes (four-membered rings fused to 6,6 junctions) are typically formed upon [2+2] cycloadditions. Basically these types of cycloadditions are less common, with the first reported example being the thermal [2+2] cycloaddition of benzyne to C60 [49,50]. 

In an another mechanistic study, Foote and co-workers reported a possible charge-transfer mechanism for the photochemical [2+2] cycloadditions of electron-rich ynamines [56-58]. Further studies on the regio- and stereoselectivity upon addition of less electron-rich substrates such as alkyl-substituted 1,3-bu-tadienes [59], acyclic enones [60], and aryl alkenes [61] to C60 were performed in more recent years. 

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Novel EPMEs based on carbon paste impregnated with (1,2-methanofullerene C60)-61-carboxylic acid (I), diethyl (1,2-methanofullerene C60)-61-61-dicarboxylate (II) and tert-butyl (1,2-methanofullerene C60)-61-carboxylic acid (III) were designed for the assay of S-clenbuterol raw material and in serum samples [52], All EPMEs showed near-Nemstian responses (56.8, 57.0 and 57.1mV/decade of concentration) for S-Clen, with correlation coefficients for the equations of calibration of 0.9996 (I), 0.9998 (II) and 0.9998 (III), respectively, and low detection limits (of lO-10 and 10 11mol/L magnitude order). R-Clen, on the other hand, showed non-Nemstian response. All electrodes displayed good stability and reproducibility over 1-month test period, when used every day for measurements (RSD <0.1%). 

Several organofullerene donor-acceptor molecular material hybrid systems have been synthesized via 1,3-dipolar cycloaddition reactions of azomethine ylides, via Bingel cyclopropanation and methanofullerene formation intermediates as well as via cycloaddition reactions, that have already been discussed in previous sections. The majority of such hybrid systems possess always as acceptor unit the fullerene core and as donor moieties porphyrins, tetrathiafulvalenes, ferrocenes, quinones, or electron-rich aromatic compounds that absorb visible light [190-193]. The most active research topic in this particularly technological field relies (i) on the arrangement of several redox-active building blocks in... 

The need to prepare fullerene derivatives for possible applications to medicine and material sciences resulted in the development of novel synthetic methods for the functionalization of Cso. R. Pellicciari et al. reacted Ceo with carboalkoxycarbenoids generated by the Rh2(OAc)4-catalyzed decomposition of a-diazoester precursors. This reaction was the first example of a transition metal carbenoid reacting with a fullerene and the observed yields and product ratios were better than those obtained by previously reported methods. The reaction conditions were mild and the specificity was high for the synthesis of carboalkoxy-substituted[6,6]-methanofullerenes. When the same reaction was carried out thermally, the rearranged product (the [6,5]-open fullerene) was the major product. 

Figure 2.56 collects some exemplary reactions of Ceo with different bromoma-lonates and other applicable keto compounds. This collection shows that there is virtually no Umit to the choice of side chains, which renders the Bingel-Hirsch reaction an attractive and flexible starting point for the synthesis of fuUerene-containing materials. For example, the base-mediated conversion of a malonate and Cao into the respective methanofullerene can also be achieved. With the semiester of malonic acid instead of a malonate, the monosubstituted methanofullerene is obtained because the primary product is instantaneously decarboxylated (Figure 2.56). P-Ketoesters may also be reacted under Bingel-Hirsch conditions to give methanofuUerenes.

In general, the methanofullerenes formed by the Bingel reaction are stable and have been used widely for the synthesis of new materials. However, as a drawback, they show liability under reductive conditions. Electrochemical reduction is sufficient to induce a reverse Bingel reaction in di(alkoxycarbonyl)methanofullerenes, generating the parent fullerene and starting malonate as products. ... 

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