Fullerene-crown ether conjugates

Transesterification of the fullerene crown ether conjugate (+)-89 allowed for the removal of the tether, leading to the D2fj-symmetrical bisadduct 94 (34%) [93], which is a very useful building block for further addition chemistry. 

A few other interesting molecular architectures exhibiting uncharacteristic electrochemical behavior have been constructed on the basis of the methanofullerene building block. These include two methanofullerene-substituted bipyridine ligands complexed to rhenium and ruthenium ((35) and (36) in Fig. 17), which were prepared as possible candidates for photoinduced electron transfer processes [138]. In addition, three fullerene crown ether conjugates ((38), (39), and (40) in Fig. 18) have... 

Electrochemical studies of fullerene crown ether conjugates (38), (39), and (40) yielded fascinating results. The three compounds differ only in the points of attachment of the tangential crown... 

Bourgeois, J.-P. Echegoyen. L. Fibbioli, M. Pretsch, E. Diederich. F. Regioselective synthesis of trans-l fuller-ene i.v-adducts directed by a crown ether tether Alkali metal cation modulated redox properties of fullerene-crown ether conjugates. Angew. Chem. Int. Ed. 1998. 37. 2118-2121. 

Fig. 18. A self-assembled fullerene-crown ether conjugate monolayer.

A fullerene-crown ether conjugate, similar in structure to that used for building SAM associates, forms in solution a 1 1 complex with 3-aminomethyl-(2,2,5,5-tetramethylpyrrolindin-l-oxyl). Using visible light, which engages mainly with the fullerene core, a radical-triplet pah-in the quartet excited state has been recorded. Strong electronic interactions between the triplet excitations and an ammonium aminoxyl free radical are responsible for the radical-triplet character. 

A methanofullerene derivative possessing an ammonium subunit has been prepared and subsequently shown to form a supramolecular complex with a porphyrin-crown ether conjugate <06T1979>. The synthesis and study of these fullerene-containing supramolecular photoactive devices have also been reported <06CRC1022>. 

Importantly, the tethers in these bisadduds can be readily removed, making them true templating units. This point is illustrated by the cleavage of the crown ether tether in conjugate 24 to give untethered trans-1 fundionalized fullerenes that are of interest for use as further molecular scaffoldings (Scheme 5).156 60 611... 

The conjugation in the molecular wire may be disrupted or modulated to create systems with different properties. For example, a porphyrin Ceo donor-acceptor system linked with a conjugated binaphthyl unit, has a preference for the atropi-somer where the fullerene unit is closer to the porphyrin system, thus increasing the through space interactions [82]. The charge transfer process on a dyad containing a crown ether in the linker structure can be modulated by complexation/ decomplexation of sodium cations [83] but even more interesting is the construction of supramolecular systems where the donor and acceptor moieties are... 

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