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

Abstract

Representatives of two classes of hexakis-adducts of C 60 were prepared by templated synthesis strategies. Compound 8 with a dipyridylmethano addend in a pseudo-octahedral addition pattern was obtained by DMAtemplated 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 C 60 moieties as part of the polymeric backbone ( Fig. 1).With the residual fullerene p-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, (AE)-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 (AE)-1, p-electron conjugation between the two unsubstituted poles of the carbon sphere is maintained via two (E)-stilbene-like bridges (Fig. 4). As a result, (AE)-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, (AE)-30 and (AE)-31, respectively (Scheme 6). The different extent of the residual p-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 (AE)-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.1. Introduction. ± Among the higher adducts of buckminsterfullerene (C 60 ; for a recent example, see [1]), hexakis-adducts are increasingly attracting interest as threedimensional scaffolds for advanced materials applications [2] [3]. Among those, derivatives with a pseudo-octahedral (T h ) addition pattern have been the earliest and most widely investigated ones [4 ± 8]. Also known is a hexakis-adduct with a D 3 -symmetrical addition pattern [2]. Both types of hexakis-adducts are accessible by stepwise additions, and their addends are evenly distributed over the entire carbon sphere. In this paper, we describe the synthesis of new hexakis-adducts with the T hsymmetrical addition pattern, which are useful...

Tether-directed remote functionalization of fullerenes C60 and C70

“…Acid-catalyzed cleavage of the tertbutyl ester groups and the crown ether template afforded the corresponding tetracarboxylic acid 19 which was transformed over several steps into tetrol 20 and further into tetrakismalonate 21. The final step of the sequence, affording D 2 -symmetric hexakisadduct (±)-22 as sole product [29,40], consisted of two double tether-directed remote Bingel additions, multiple macrocyclizations which had previously been described as 'clipping reactions' and given access to tris-and tetrakisadducts of C 60 [41]. X-ray crystallography of (±)-22 confirmed all six cyclopropane rings to be arranged in a double-helical fashion with the corresponding axis passing through the unfunctionalized poles of the carbon sphere.…”

“…However, following a multistep procedure by An et al [25], transformation of the fullerene-fused cyclohexene to cyclohexadiene units (7, Scheme 2) and in situ treatment of the latter with dimethyl acetylenedicarboxylate afforded, in a DielsAlder/retro-Diels-Alder sequence, tetrakisadduct 8 which was finally transesterified to octakis(ethyl ester) 9 [26,27]. As confirmed by X-ray crystallography [27], 9 includes two 6-6 bonds in all-e position relative to the addends in place which can be exploited for further molecular scaffolding [28,29]. Tetrakisadduct 9 was obtained independently by Kräutler and co-workers, as reported by Schwenninger et al [22] and Kräutler et al [30], through a completely different template-directed approach including, as a key step, a topochemically controlled, regioselective anthracene transfer in heated crystals of the monoadduct resulting from Diels-Alder addition of anthracene to C 60 [22,30].…”

“…This constitution leads to rather different chemical reactivity and physical properties in comparison to the pale yellow hexakisadducts with a pseudo-octahedral addition pattern (e.g., 4, Scheme 1). Hexacyclopropafullerene (±)-22 readily undergoes further Bingel additions at the two sterically most accessible polar 6-6 bonds under formation of orange-yellow heptakis-and octakisadducts [29,40].…”

Fullerodendrimers: Fullerene-Containing Macromolecules with Intriguing Properties

“…The UV/Vis spectra of 5-8 show all the characteristic features seen for previously reported analogous cis-2 bis-adducts [8]. In addition, it must also be added that 1,3-phenylene bis(methylene)-tethered bis-malonates produce regioselectively the cis-2 addition pattern at C 60 [26][27][28][29][30].…”

Self‐Organizing Surface‐Initiated Polymerization of Multicomponent Photosystems: Stack Exchange with Fullerenes

“…One TEG solubilizer 6 was attached to malonic acid 7 as described (Scheme 1). 2c The resulting malonate monoester 8 was reacted with the primary alcohols in diol 9 to give bis-malonate 10 . Diol 9 was prepared as described by Nierengarten et al2a Namely, 3,5-dibromobenzaldehyde 11 was protected as acetal 12 and formylated by treatment with first tert -butyl lithium ( t BuLi) and then N,N -dimethylformamide (DMF).…”