Electrochemically Induced Retro‐Cyclopropanation Reactions

Abstract

The efficient removal of methano addends from fullerenes using reductive electrochemistry is a versatile and useful reaction, which was initially called the retro-Bingel reaction since it was observed for the first time on bis(alkoxycarbonyl)methano adducts, commonly known as Bingel adducts. Since its initial discovery, this reaction has been successfully employed in the separation of enantiomers and constitutional isomers of fullerenes, which in some cases were otherwise not accessible. Even more interesting than the retro-Bingel reaction was the electrochemically induced isomerization that bis-methano adducts of C 60 exhibit, and which was referred to as the ''shuffle''. The combination of both reactions gave interesting results during the electrolysis of tetrakis-, pentakis-, and hexakis-Bingel adducts of C 60 . The selective removal of Bingeltype addends, while leaving other addends undisturbed, was also investigated. More recently, it was observed that in addition to bis(alkoxycarbonyl)methano adducts, electrochemical Spain in 1972. She received her B.Sc., M.Sc., and PhD degrees in 1995 MICROREVIEWS: This feature introduces the readers to the authors' research through a concise overview of the selected topic. Reference to important work from others in the field is included. reduction of other methano adducts, such as spiromethanofullerenes, could also result in removal of the methano addends, thus the reaction was more generally denoted as retro-cyclopropanation. In some of the spiromethanofullerenes investigated, and depending on the solvent used, an electrochemically induced intermolecular addend transfer was observed, which provided a regioisomeric distribution that differed significantly from that obtained by a synthetic route. We have recently shown that singly bonded dimers are formed as intermediates during retro-cyclopropanation reactions. In this microreview, we describe the general observations that led to the initiation of these exciting electrochemical investigations, review the differences between the chemical and electrochemical methodologies in retro-cyclopropanation reactions and explore the mechanisms involved during addend removal.

Electron Donor–Acceptor Interactions in Regioselectively Synthesized exTTF2–C70(CF3)10 Dyads

“…The voltammogram turned out to be irreversible at the second reduction potential, at which a retro-cyclopropanation reaction probably occurs. [24] On the oxidation side, the two-electron quasireversible oxidation, forming the exTTF dication directly, is observed at E 1 ox = + + 0.07 V. [25] Similar redox potentials, as found for 3 and 2, reveal, in agreement with the data stemming from the electronic spectra, only weak interactions between the redox chromophores in their ground state.…”

Isomeric and Structural Impacts on Electron Acceptability of Carbon Cages in Atom-Bridged Fullerene Dimers

“…This reduction was not ascribed to the carbon-bridged fullerene dimers but to intermediates arising from rearrangement or dissociation of the C 2m dCdC 2n dimers; i.e., different species formed by an irreversible chemical process occurred with the reduction reactions, as those reported for other fullerene derivatives. [24][25][26][27] For instance, the homofullerene is able to rearrange into the methanofullerene under the conditions of the electrochemical reduction. 28,29 Controlled Potential Electrolysis (CPE) of C 121 (I).…”

“…24 The derivatives with phosphonate or sulfone groups are able to lose their addend from the fullerene cage, to react with another molecule or to form a dimer when electrochemistry is performed. 26 C 120 undergoes dissociation into a C 60 anion under electrochemical reduction.…”

Chemical, Electrochemical, and Structural Properties of Endohedral Metallofullerenes

“…Other methods include electrochemical and chemical separations of EMFs from the extracted soot. These methods take advantage of the considerably large HOMO-LUMO gaps of empty fullerenes such as C 60 and C 70 . EMFs are more easily oxidized or reduced, then extracted with polar solvents to finally be reduced or oxidized, thereby obtaining neutral EMFs that can be easily separated by HPLC.…”

“…[58] An extensive study of these derivatives later concluded that the [6,6] regioisomer has a very high stability, since no retrocycloaddition of 18 a took place (in contrast to C 60 ). [70] The methanofullerene 18 c synthesized with Y 3 N@C 80 was identified by X-ray diffraction as a fulleroid in which the addition bond is broken (see C1-C9 in Figure 10). The [6,6] bond of the addition site is indeed open and, in contrast to the crystal structure of the methanopyrrolidino 13 b derivative, one metal ion points directly towards the open bond.…”