Buckminsterfullerenes / Organodihydrofullerenes / Fullerene derivatives Controlled two-step nucleophilic hydroalkylations, hydroar-formed. In all cases the addition takes place at a double bond ylations as well as hydrostannylations of fullerene-60 (1) and separating two six-membered rings of the fullerene core. In fullerene-70 (2) lead to defined organodihydrofullerenes this way a variety of organodihydrofullerenes also carrying CWHR and C,,HR. NMR investigations show that only one functional groups have been synthesized. isomer of each organodihydrofullerene with C, symmetry is
The spherical all-carbon Ih molecule fullerene-60 (C,) consists of 12 isolated pentagons and 20 hexagons. Structural data"] and calculations[*] demonstrate that the bonds between two hexagons (6 -6 bonds) exhibit double-bond character. The bonds between the pentagons and hexagons (5 -6 bonds) with single-bond character are significantly longer, also showing a much lower electron density. Therefore, fullerene-60 can be considered a sphere built up of fused [Slradialene and cyclohexatriene units. This structural argument is supported by its chemical reactivity. One-step additions to c60, namely the addition of osmium tetroxide['], transition-metal complexes[41 or 1,3-dipolesr5I, exclusively take place at the 6-6 bonds. The other important chemical property of Cs0 (1) is its high electrophilicityt6I and affinity towards radicals[71. Due to the polyfunctionality (thirty 6 -6 bonds), an uncontrolled reaction leads to a huge number of different addition products which are impossible to isolate. Only few examples for the preparation of isomerically pure single compounds are k n ~w n [ ' -~, * -~' ~ . R ecentlyP1, we have shown that it is possible to control even two-step nucleophilic additions to a 6 -6 bond and to isolate the isomerically pure organodihydrofullerenes 1-tert-butyl-and l-ethyl-l,9-dihydrofullerene-60"*l (5b and 5c). Thereby 1 was titrated with tert-butyllithium or ethylmagnesium bromide and subsequently protonated under HPLC control. This method opens up the access to a variety of functionalized organodihydrofullerenes which for example can serve as precursors for further reactions. Independently, 5b was prepared by Fagan et al. using another procedure[131. The experi-