Hexakis-Adducts of [60]Fullerene with Different Addition Patterns: Templated Synthesis, Physical Properties, and Chemical Reactivity

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Abstract

Representatives of two classes of hexakis-adducts of C60 were prepared by templated synthesis strategies. Compound 8 with a dipyridylmethano addend in a pseudo-octahedral addition pattern was obtained by DMA-templated addition (DMA=9,10-dimethylanthracene; Scheme 1) and served as the starting material for the first supramolecular fullerene dimer 2. Hexakis-adduct 12 also possesses a pseudo-octahedral addition pattern and was obtained by a sequence of tether-directed remote functionalization, tether removal, and regioselective bis-functionalization (Scheme 2). With its two diethynylmethano addends in trans-1 position, it is a precursor for fascinating new oligomers and polymers that feature C60 moieties as part of the polymeric backbone (Fig. 1). With the residual fullerene π-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 steps (Schemes 3 and 5). In compound (±)-1, π-electron conjugation between the two unsubstituted poles of the carbon sphere is maintained via two (E)-stilbene-like bridges (Fig. 4). As a result, (±)-1 features very different chemical reactivity and physical properties when compared to hexakis-adducts with a pseudo-octahedral addition pattern. Its reduction under cyclic voltammetric conditions is greatly facilitated (by 570 mV), and it readily undergoes additional, electronically favored Bingel additions at the two sterically well-accessible central polar 6-6 bonds under formation of heptakis- and octakis-adducts, (±)-30 and (±)-31, respectively (Scheme 6). The different extent of the residual π-electron delocalization in the fullerene sphere is also reflected in the optical properties of the two types of hexakis-adducts. Whereas 8 and 12 are bright-yellow (end-absorption around 450 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 not accessible by stepwise synthetic approaches.

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