Fullerene-ferrocene hybrid

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... 

Ferrocene is composed of a pair of 6-7r-electron carbon arrays and a 6-d-electron iron(II) atom. Ferrocene-fullerene donor-acceptor dyads carry all the requisites for electron-transfer phenomena. However, data for the formation of ferrocene-fullerene hybrids are not abundant. Some such dyads have already been synthesized following the methodology of 1,3-dipolar cycloaddition of the appropriate azome-thine ylides to C60, with either variable-spacing building blocks or a rigid-bridge all-cj-bonded framework, in order to tune the redox properties of the system [40,234, 248-251]. Another novel dyad that contained two covalently bound ferrocene units was recently synthesized via cyclopropanation of the fullerene core [252]. 

Recently, hybrids of a fullerene and a ferrocene have been reported in which an ion is sandwiched between a ti -C5H5 ring and a it -fullerene, shown in Figure 13-38(b). The fullerenes used, Cbo(CH3)5, and C7o(CH3)3, have methyl groups that apparently help stabilize these compounds. The methyl groups are bonded to carbons adjacent to the 5-membered ring to which the iron bonds. 

Hybrids of a fullerene and a ferrocene have been reported in which an ion is sandwiched between a ring and a rj -fullerene (Figure 13.41b). The fullerenes used,... 

Figure 20 Redox gradient in the hybrid self-assembled system composed of fullerene derivative, positively charged porphyrin, negatively charged porphyrin and ferrocene with positively charged pyridinium anchor. (Reproduced from Ref. 102. Royal Society of Chemistry, 2004.)...

The idea of the fusion of a molecule of ferrocene with a molecule of fullerene is intriguing since such a bucky ferrocene would exhibit the properties of both parent molecules. Very recently professor Eiichi Nakamura, University of Tokyo, with his collaborators synthesized such a ferrocene/ fullerene hybrid molecule by a route as depicted in Figure 15.12.1. The route involved a suitably modified fullerene derivative that can act as a 6ji-electron donor to the d iron(II) atom. By heating C6oMe5H (1) and [FeCp(CO>2]2 (Cp = cyclopentadienyl) together in benzonitrile at 180 °C for 8 hours, the product (2) was obtained in 52% isolated yield. 

Figure 15.12.1. Synthesis of ferrocene/fullerene hybrid molecule (2). The single and double bonds in fullerene are only formal, as for fullerene itself. (Reproduced by permission from the principal author E. Nakamura, and from the American Chemical Society.)...

The hybrid molecule can not only be oxidized reversibly like ferrocene but it can be reduced reversibly like fullerene. This offers a very special com-... 

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