Synthesis of Functional Organometallic Complexes Involving a Pentahaptofullerene Ligand

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The pentaphenylated fullerene anion C_<60>Ph_5-, which is obtained through the five-fold addition of an organocopper reagent to C_<60>, and its metal complexes represent a new class of cyclopentadiene derivatives, which can be prepared through deprotonation of the parent compond. One out of twelve pentagons in C_<60> is isolated from the remaining 50 sp^2 carbon atoms of the C_<60> molecule by five surrounding sp3 carbon atoms each bearing a phenyl group. The previous X-ray crystallographic studies revealed the highly unique cavity structure formed around the cyclopentadienyl (Cp) moiety by the five phenyl groups, but failed to give us information on the electronic properties of these unique molecules. In this research project, we have carried out ab-initio molecular orbital calculations and electrochemical experiments and obtained evidence that there is endohedral homoconjugation, that is, an electronic interaction between the upper Cp and the lower C_<50> moiety in C_<60>Ph_5-and C_<60>Ph_5H through inside of the C_<60> cage.We also found that the reaction of C_<70> with an organ ocopper reagent gives a trisaddition product [C_<7O>Ar_3H, Ar = 4-CF_3-C_6H_4] with an indene-like substructure flanked by the three sp^3 carbons in a quantitative yield. The trisadduct was deprotonated with metal alkoxides to form the corresponding metal complexes C_<70>Ar_3M [M=K, Tl]. The results of ab initio molecular orbital calculations and X-ray diffraction study suggested that C_<70>Ar_3- coordinates to the metal as an eta^5-indenylide rather than a eta^3-ligand in C_<7O>Ar_3M.