Unprecedented ring expansion of C60: difluoromethylene[60]fullerenes and their hydrides

After discovery of fullerenes there were offered a wide variety of ways of their practical use. Nowadays a lot of patents in the field of fullerene chemistry concern use of fullerenes and nanotubes in semiconductor and nanoeletronic devices, e.g. photodiodes, transistors, sun batteries. Due to high electronegativity, fullerene C60 can easily form charge-transfer complexes in which it acts as acceptor of electrons. Light irradiation of fullerene-based dyads (consisting of an electron-acceptor fullerene cage covalently bonded with photoactive donor part) results in intermolecular and supramolecular photoinduced electron transfer processes. High efficiency of light absorption and charge separation lies in a basis of the working principle of photovoltaic cells. Accordingly, research on fullerene derivatives with enhanced electronegativity is an important task. Due to high electronegativity of fluorine atom, its addition to fullerenes leads to increase in their electron-acceptor properties. Therefore research on fluorine-containing fullerene derivatives is a matter of great interest. In this work there were carried out synthesis, isolation and investigation of electrochemical properties of two simplest representatives of the new class of fullerene fluorides: С60(CF2) and C60(CF2)2. It was shown that addition of CF2-bridge to fullerene leads to a considerable shift of reduction potential: [6,6]-open C60(CF2) and cis-2C60(CF2)2 undergo reversible reduction at potentials, 150 and 145 mV more positive than that of C60. Structure, electron shell structure and lifetimes of anion-radicals obtained by reduction were determined by means of EPR and DFT calculations. It was shown that monoanions of compounds in question preserve the methylene bridge. Protonation of monoanion-radical of C60(CF2) in o-DCB with strong H-acid leads to formation of 1,9-dihydro-(1a,1a-difluoro-1aH-1(9)а-homo(C60Ih)fullerene, C60(CF2H2). This compound is the first characterized derivative of [6,6]-open C60(CF2). According to UV-vis spectroscopic, MALDI mass-spectroscopic and Н и F-NMR data, it has [6,6]-open structure.