Hexakis-adducts of [60]fullerene with different addition patterns: Templated synthesis, physical properties, and chemical reactivity

Representatives of two classes of hexakis-adducts of C-60 were prepared by templated synthesis strategies. Compound 8 with a dipyridylmethano addend i n a pseudo-octahedral addition pattern was obtained by DMA-templated additi on (DMA = 9,10-dimethylanthracene; Scheme 1) and served as the starting mat erial for the first supramolecular fullerene dimer 2. Hexakis-adduct 12 als o possesses a pseudo-octahedral addition pattern and was obtained by a sequ ence of tether-directed remote functionalization, tether removal, and regio selective bis-functionalization (Scheme 2). With its two diethynylmethano a ddends in trans-1 position, it is a precursor for fascinating new oligomers and polymers that feature C-60 moieties as part of the polymeric backbone (Fig. 1). With the residual fullerene, pi -electron chromophore reduced to a 'cubic cyclophane'-type sub-structure (Fig. 4), and for steric reasons, 8 and 12 no longer display electrophilic reactivity. As a representative of the second class of hexakis-adducts, (+/-)-1, which features six addends in a distinct helical array along an equatorial belt, was prepared by a route that involved two sequential tether-directed remote functionalization step s (Schemes 3 and 5). In compound (+/-)-1 pi -electron conjugation between t he two unsubstituted poles of the carbon sphere is maintained via two (E)-s tilbene-like bridges (Fig. 4). As a result, (+/-)-1 features very different chemical reactivity and physical properties when compared to hexakis-adduc ts with a pseudo-octahedral addition pattern. Its reduction under cyclic vo ltammetric conditions is greatly facilitated (by 570 mV), and it readily un dergoes additional, electronically favored Bingel additions at the two ster ically well-accessible central polar 6-6 bonds under formation of heptakis- and octakis-adducts, (+/-)-30 and (+/-)-31, respectively (Scheme 6). The d ifferent extent of the residual pi -electron delocalization in the fulleren e sphere is also reflected in the optical properties of the two types of he xakis-adducts. Whereas 8 and 12 are bright-yellow (end-absorption around 45 0 nm), compound (+/-)-1 is shiny-red, with an end-absorption around 600 nm. This study once more demonstrates the power of templated functionalization strategies in fullerene chemistry, providing addition patterns that are no t accessible by stepwise synthetic approaches.