The Application of Electron Shuttles

One obstacle in the reduction of carbon-rich molecules using alkali metals is their low solubility, especially when the compounds are large however, the anions of such compounds are soluble in THF. One way to overcome this difficulty is by using another carbanion as an intermediate reagent to aid the electron transfer. In this manner, the soluble carbanion can effectively transfer electrons to the compounds of low solubility and thus reduce them. This method was used already in 1960 by both Homer and Normant, who used the radical anion of 1 for a variety of 

The new carbon allotropes, fullerenes [14] and nanotubes [15], can accept a large number of electrons to their -system however, the neutral compounds are hardly soluble, especially in THF. Because of the low solubility of fullerenes, their complete reduction to hexaanions with Li is possible only under extreme conditions, such as the use of an ultrasound bath [16], When the reduction of fullerenes is performed in the presence of a small amount of 2, moderate conditions are required, e.g., low temperature and without sonication [17]. Corannulene, which is a fragment of fullerenes, is highly soluble in THF and is easily reduced. The resulting corannulene anion serves as an efficient electron shuttle, which assists in complete reduction of the practically insoluble fullerenes. In a similar way, single walled nanotubes were reduced by charge transfer by the use of small aromatic compounds, such as naphthalene, fluorenone and anthraquinone [18]. 

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