Novel fluorene-containing fullerenes C60: synthesis and structures

Abstract

Reactions of fullerene C 60 with fluorene 2 carbaldehyde or 2,7 diacetylfluorene in toluene gave novel spiromethanofullerenes containing a reactive free formyl group. A novel fluorene containing fullerenopyrrolidine was obtained by the Prato reaction. The purity and com positions of the compounds obtained were confirmed by MALDI TOF mass spectro metry and HPLC. Their structures were confirmed by 2D homo and heterocorrelation NMR techniques.The chemistry of fullerenes has much advanced in the study of the Bingel-Hirsch 1,2 and Prato reactions 3 yield ing methanofullerenes and fullerenopyrrolidines. These compounds are stable and their properties strongly de pend on the nearest environment in the attached addend. For this reason, more and more attention is being given to their derivatives containing fragments of polycyclic hydro carbons or heterocycles. The presence of such fragments can impart unusual photophysical properties to the re sulting compounds.Here we describe a method for the synthesis of novel fluorene containing spiromethanofullerenes and fullerenopyrrolidine. The distinctive feature of spiro methanofullerenes is the spatial orientation of the addend rigidly bound to the methano fragment. These compounds can exhibit specific properties of addends. Fluorene con taining fullerenes C 60 are promising as precursors of do nor-acceptor polymeric products, as well as for creation of film and layered electron and photoconductive and light emitting materials. 4Up to date, fluorene containing methanofullerenes have been obtained according to Wudl´s method 5,6 through intermediate diazo compounds. The electro chemical properties of the resulting compounds have been also studied. 5,6 Here we synthesized novel fluorene con taining fullerene derivatives by the Bingel-Hirsch and Prato reactions. 1-3 Results and DiscussionThe acidity of the methylene H atoms in fluorene and its derivatives is sufficient for in situ preparation of bromo derivatives in base catalyzed reactions with CBr 4 . Carb anions generated in reactions of bromofluorene with a base add to the double bond of fullerene to give methano fullerene. The room temperature Bingel-Hirsch reac tions 1,2 of fullerene C 60 with fluorene 2 carbaldehyde and 2,7 diacetylfluorene in the presence of CBr 4 and DBU gave the corresponding fluorene containing spiro methanofullerenes 1 and 2. Compounds 1 and 2 were isolated by column chromatography on SiO 2 in 12.3 and 17.3% yields, respectively.The presence of two fullerene reactive groups in the starting fluorene 2 carbaldehyde allows one to obtain two types of fullerene derivatives: spiromethanofullerene 1 and fullerenopyrrolidine 3. For the synthesis of the latter, a mixture of fullerene C 60 , N methylglycine, and fluo rene 2 carbaldehyde was refluxed in toluene under dry argon for 8 h. The composition of the reaction mixture was monitored by HPLC. Fullerenopyrrolidine 3 was iso lated by column chromatography on SiO 2 in 16.1% yield (with respect to the consumed fullerene). The reactivities of fullerenes 1-3 toward ...

Decatungstate‐Photocatalyzed Radical Addition of 9‐Substituted Fluorenes to [60]Fullerene: A Mechanistic Approach

“…Up to date, many examples of [60]fullerenes containing a fluorene moiety have been published [17–20] . However, the synthesis of all those fullerene derivatives, requires the use of a linker moiety for attaching the fluorene or fluorene derivatives into the fullerene core [21–24] . The linkers are usually synthesized by standard experimental procedures, namely the 1,3 dipolar cycloadditions of azomethane ylides, [21] the Bingel reaction, [22–24] and more recently a new platinum‐catalyzed [2+2] cycloaddition reaction [25] .…”

“…However, the synthesis of all those fullerene derivatives, requires the use of a linker moiety for attaching the fluorene or fluorene derivatives into the fullerene core [21–24] . The linkers are usually synthesized by standard experimental procedures, namely the 1,3 dipolar cycloadditions of azomethane ylides, [21] the Bingel reaction, [22–24] and more recently a new platinum‐catalyzed [2+2] cycloaddition reaction [25] . However, a new, versatile and attractive synthetic route that could facilitate a one‐step, efficient approach to the C 60 ‐fluorene direct coupling, has yet to be developed.…”

Nucleophilic cyclopropanation of [60]fullerene by the addition–elimination mechanism

“…For example, information is available that spiromethanofullerenes containing a reactive free formyl 341 and diacetyl 342 groups were synthesized by the Bingel-Hirsch process (Scheme 95). 162 Meldrum's acid derivatives are also original cyclopropanating agents. Under Bingel-Hirsch reaction conditions, they gave a number of methano derivatives 343-353 in moderate yields (Scheme 96).…”