Selective oxidative conversion of triaryldihydro[C59N]fullerenes: a model case for oxygenation of carbon allotropes

Abstract

The photooxidation of triaryldihydro [C 59 N]fullerenes was achieved by treatment with air and light leading to a new selective core functionalization of azafullerenes, which serves as a model case for oxygenation of carbon allotropes.To date, azafullerenes, in which one carbon atom of the C 60 skeleton is substituted by nitrogen, are the only class of heterofullerenes that are accessible in macroscopic quantities. 1,2 In general, carbon allotropes like fullerenes, carbon nanotubes and graphene represent an emerging research field. 3-5 Particularly, graphene based materials have gained enormous attention due to their fascinating electronic properties. 6 In this regard, graphene oxide 7 plays an important role as a promising precursor for wet chemical synthesis of graphene with minimal defects. 8 Its structure contains epoxy and hydroxyl groups in addition to carboxylic acids at the edges of the graphene oxide layers according to the Lerf-Klinowski model. 9,10 However, the oxygenation mechanism behind structures like graphene oxide is still not understood. Even the structure elucidation is still in progress. 11 In addition, the chemical doping of graphene with nitrogen leads to promising materials that have already shown superior preferences towards various applications. 12 However, chemical reactions on N-doped graphenes are an unaddressed issue. In this context, fullerenes, in general, provide a very suitable model system to study oxygenation reactions and the stability of products due to their monodispersity and the possibility of using unambiguous characterization methods such as mass spectrometry, NMR spectroscopy and X-ray single crystal analysis. Here, we report on selective oxygenation reactions of azafullerene derivatives providing valuable insights into carbon allotrope oxides and their formation mechanism.The azafullerene dimer can be obtained by a three-step reaction starting from C 60 . 1,2 Covalent functionalization of C 59 N monoadducts such as C 59 NAr has been investigated quite extensively; 13,14 however, heterofullerene derivatives with a higher degree of addition have only been generated in a few cases, 15-21 in contrast to the corresponding rich chemistry of the isocyclic fullerene C 60 . However, the establishment of a C s -symmetrical 6,8,12,15,18-addition motif, also known for C 60 fullerene derivatives, 22,23 was first demonstrated by our group with the successful synthesis of tetrachlorinated aryladduct C 59 NArCl 4 bearing an integral pyrrole moiety within the p-system of the fullerene surface. 16 Recently, we explored the formation of pentaarylazafullerene C 59 NAr 5 by an acid catalyzed reaction of a C 59 N precursor with electron-rich aromatic compounds. During the course of these reactions, triaryldihydroazafullerenes C 59 NAr 3 H 2 1-4 were formed as stable intermediates. 20,21 Furthermore, they exhibit the same pentakisaddition pattern, but contain an unusual pyrrole substructure with allylic hydrogen atoms. The reactivity of these triaryldihydroazafullerenes is still unexplored,...

Chemistry with Graphene and Graphene Oxide—Challenges for Synthetic Chemists

“…In this regard, for example, oxygenated azafullerene derivatives have been studied in detail by using NMR spectroscopy and mass spectrometry. [148] The knowledge generated by the systematic functionalization of graphene could be a very valuable basis for exploring the chemistry of other sheet materials such as MoS 2 or even so far unknown synthetic carbon allotropes. One carbon allotrope of interest is graphyne, which is composed of sp-and sp 2 -hybridized carbon atoms arranged in a 2D crystal lattice.…”

Hydro‐aza‐(C59N)fullerenes: Formation Mechanism and Hydrogen Substitution

“…The intermediates 5 a – 10 a were isolated and characterized. The structures of 6 a , 8 a , and 3 a could be unambiguously verified by X‐ray crystallographic analysis . The two hydro‐azafullerenes 9 a and 10 a were characterized by NMR spectroscopy combined with selective synthesis of the α′‐H isomer 10 a starting from the dihydro‐azafullerene 6 a …”

“…The structureso f6a, 8a,a nd 3a could be unambiguously verifiedb yX -ray crystallographic analysis. [17,25] The two hydro-azafullerenes 9a and 10 a were characterized by NMR spectroscopyc ombined with selectives ynthesis of the a'-H isomer 10 a startingf rom the dihydro-azafullerene 6a. [17] Herein, we propose ad etailed mechanism of the entire reaction sequence shown in Scheme2.T his includes the dihydro adducts 5a-8a exhibiting different additionp atterns (Scheme 2 i), ii), and iii)).…”

ChemInform Abstract: Azafullerene C59N in Donor—Acceptor Dyads: Synthetic Approaches and Properties

“…Compared to C 60 derivatives, azafullerenes have al ower energy of the S 1 state (by 0.27 eV), almosth alf fluorescenceq uantum yield and lifetimea nd lower quantum yield for the ISC (F T % 1f or C 60 derivatives).A dditionally,a sw ell as C 60 ,a zafullerene is also as inglet oxygen sensitizer. [12] Regarding electrochemistry,a zafullerene derivatives usually exhibit three quasi-reversible reductionw aves, as in the case of C 60 ,b ut usually in more positive potentials. All in all, Ndoping of the fullerenes phere with an itrogen atom results in al ower singlet excited state energy and easier reduction, making C 59 Nd erivatives potentially better energy-and electron-acceptors than those of C 60 .…”