Fullerene dendron

Preparation of mono-adducts of fullerene - for studies on electrostatic interactions - was undertaken by cyclopropanation of fullerene with appropriately functionalised malonic esters 1 (Bingel reaction) to form 2. Coupling with the tert-butyl protected oligoamide-amino-dendron 3 and subsequent hydrolysis lead to the water-soluble fullerene dendron 5, which can carry up to nine negative charges after depro to nation. After association with the zinc complex of cytochrome C, photoinduced electron transfer (PET) from the redox protein to the fullerene can be accomplished, which was studied by fluorescence spectroscopy. 

Fullerenes possess electronic and photophysical properties which make them natural candidates for the preparation of functional dendrimers. The attachment of a controlled number of dendrons on a core provides a compact insulating layer around the carbon sphere, and the... 

FuUerodendrimers also allow an evaluation of the accessibility of the Cgo core unit by studying bimolecular deactivation of its excited states by external quenchers. Recently Ito, Komatsu, and co-workers have used this approach to investigate a series of fuUerodendrimers (9-11) in which Frechet-type dendrons have been connected to a fullerene moiety via an acetylene linker (Fig. 5) [35]. 

All the fullerene-containing dendrimers reported to date have been prepared with a Cgo core but never with fullerene units at their surface or with Cgg spheres in the dendritic branches. We have recently started a research program on the synthesis of dendrons substituted with fullerene moieties. These fulleroden-drons are interesting building blocks for the preparation of monodisperse fullerene-rich macromolecules. In addition, they are also amphiphilic compounds capable of forming stable Langmuir films at the air-water interface. 

Dendrons 21-23 are easily prepared on a multi-gram scale and are highly soluble in common organic solvents thanks to the presence of the four long alkyl chains per peripheral fullerene unit. Therefore, they appear to be good candidates for the preparation of fullerene-rich macromolecules, for example, as shown by their attachment to a phenanthroline diol derivative and the preparation of the corresponding copper(I) complexes (see below). 

Fullerene derivative 34 substituted with two long alkyl chains (solubilizing groups) and a carboxylic function was used as peripheral subunit for the constructions of the dendrons (Fig. 14). 

However, transfer of the monolayers to solid substrates was inefficient because of the small size of the hydrophilic anchor, which imparted a hydrophobic/hydrophilic imbalance. Accordingly, increasing the size of the hydrophilic anchor facilitated the formation of stable Langmuir films that could be transferred to sohd substrates with a transfer ratio of 1 (Nierengarten et al. 2001). Bayer s research group reported a related approach in which the fullerene was modified with carboxylate-terminated dendrons and alkyl chains (Maierhofer et al. 2000). This amphiphilic fullerene derivative formed stable monolayers that could be compressed and expanded without hysteresis (Fig. 11.46d Maierhofer et al. 2000). 

Another example of fullerene-rich dendrimers consist of a Cu(I) bis-phenanthro-line complex as core, linked to four dendrons, each one containing 1,2 (compound 28 in Fig. 6.22), or 4 fullerene moieties appended at the periphery.77... 

Over the past 15 years, we have assisted in a huge development of the covalent chemical functionalization of the Ceo carbon sphere aimed at generating many new fullerene-based materials,6 7 in which the outstanding properties of the fullerenes would combine synergistically with those of other molecular materials, polymers, dendrons, liquid crystals, and more, in general, with photo-, electro-, or biologically active units (Scheme 9.1). 

A metallodendrimer with a copper(I) core unit coordinatively bound to phe-nanthroline ligands and whose dendrons bear terminal fullerene units was synthesised by Nierengarten el al. (Fig. 4.57) [122]. 

Wooley et al.1511 have described the creation of fullerene-bound dendrimers (Scheme 5.14). Reaction of C60 with bis(p-methoxyphenyl)diazomethane 54 and subsequent cleavage of the methyl ethers afforded a 6-6 methano-bridged fullerene (55) possessing two phenolic moieties, as the major product.1521 Treatment of the bisphenolic fullerene 55 with 2.7 equivalents of the activated dendron (52) afforded the desired substituted fullerene (56) possessing two dendritic arms. 

Scheme 5.14. Poly(benzyl ether) dendrons have been attached to fullerenes via carbenoid-type chemistry.

Wooley et al.234 reported the first dendrimer— fullerene hybrid, 165 (Scheme 21), via the alkylation of a prederivatized fullerene diphenol, 166, with the dendritic bromide 6. Because of purification problems related to impure fullerene starting material, Hawker et al. later investigated the direct cycloaddition235 of a fourth generation azide-functionalized Frechet-type dendron, 167, with Ceo- This dendritic fullerene, 168, could be easily isolated by flash chromatography and showed a significant increase in solubility over the parent fullerene. Avent et al. reported a similar cycloaddition of poly(phenylacetylene) dendrons bearing a focal tosylhydrazone functionality.236... 

Nierengarten and co-workers have described a series of ligands based upon dendron functionalized phen ligands decorated with fullerenes such as and have reported detailed studies of energy and electron transfer processes in the [CUL2] complexes. " ... 

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