Open-Cage Fullerene as Molecular Container for F- , Cl- , Br- and I. Angew Chem Int Ed Engl 2022;61:e202212090. [PMID: 36316627 DOI: 10.1002/anie.202212090]

Capturing Metal Fluoride inside a Carbon Cage

We report here a new type of metal fluoride cluster that can be stabilized inside fullerene via in situ fluorine encapsulation followed by exohedral trifluoromethylation, giving rise to rare-earth metal fluoride clusterfullerenes (FCFs) M2F@C80(CF3) (M = Gd and Y). The molecular structure of Gd2F@C80(CF3) was unambiguously determined by single-crystal X-ray analysis to show a μ2-fluoride-bridged Gd-F-Gd cluster with short Gd-F bonds of 2.132(7) and 2.179(7) Å. The 19F NMR spectrum of the diamagnetic Y2F@C80(CF3) confirms the existence of the endohedral F atom, which exhibits a triplet with a large 19F-89Y coupling constant of 74 Hz and a high temperature sensitivity of the 19F chemical shift of 0.057 ppm/K. Theoretical studies reveal the ionic Y-F bonding nature arising from the highest electronegativity of the F element and an electronic configuration of [Y2F]5+@[C80]5- with an open-shell carbon cage, which thus necessitates the stabilization of FCFs by exohedral trifluoromethylation.

Encapsulation of charged halogens by the 512 water cage

This study focuses on the encapsulation of the entire series of halides by the 512 cage of twenty water molecules and on the characterization of water to water and water to anion interactions. State-of-the-art computations are used to determine equilibrium geometries, energy related quantities, and thermal stability towards dissociation and to dissect the nature and strength of intermolecular interactions holding the clusters as stable units. Two types of structures are revealed: heavily deformed cages for F- indicating a preference for microsolvation, and slightly deformed cages for the remaining anions indicating a preference for encapsulation. The primary variable dictating the properties of the clusters is the charge density of the central halide, with the most severe effects observed for the F- case. For the remaining halides, the anion may be safely viewed as a sort of "big electron" with little local disruptive power, enough to affect the network of non-covalent hydrogen bonds in the cage, but not enough to break it. Gibbs energies for dissociation either into cavity and halide or into water molecules and halide suggest that, in a similar way as to methane clathrate, a more weakly bonded complex that has been detected in the gas phase, all halide containing clathrate-like structures should be amenable to experimental detection in the gas phase at moderate temperature and pressure conditions.

Solution Dynamics of Covalent Open-[60]Fullerene Dimers

The translational diffusivity of covalent open-[60]fullerene dimers in an organic solvent was found to be well describable by a prolate ellipsoid model while a monomeric open-[60]fullerene behaves like a sphere model. The water association dynamics were examined for two open-[60]fullerene dimers, showing a higher water affinity for the sp3-linked dimer relative to sp2-linked dimer owing to an effective orbital-orbital overlap identified by π(fullerene)→σ*(H2O) interactions as suggested by theoretical calculations.

Recent advances in supramolecular fullerene chemistry

Fullerene chemistry has come a long way since 1990, when the first bulk production of C60 was reported. In the past decade, progress in supramolecular chemistry has opened some remarkable and previously unexpected opportunities regarding the selective (multiple) functionalization of fullerenes and their (self)assembly into larger structures and frameworks. The purpose of this review article is to provide a comprehensive overview of these recent developments. We describe how macrocycles and cages that bind strongly to C60 can be used to block undesired addition patterns and thus allow the selective preparation of single-isomer addition products. We also discuss how the emergence of highly shape-persistent macrocycles has opened opportunities for the study of photoactive fullerene dyads and triads as well as the preparation of mechanically interlocked compounds. The preparation of two- or three-dimensional fullerene materials is another research area that has seen remarkable progress over the past few years. Due to the rapidly decreasing price of C60 and C70, we believe that these achievements will translate into all fields where fullerenes have traditionally (third-generation solar cells) and more recently been applied (catalysis, spintronics).

Fullerene-Functionalized Halogen-Bonding Heteroditopic Hosts for Ion-Pair Recognition

Despite their hydrophobic surfaces with localized π-holes and rigid well-defined architectures providing a scaffold for preorganizing binding motifs, fullerenes remain unexplored as potential supramolecular host platforms for the recognition of anions. Herein, we present the first example of the rational design, synthesis, and unique recognition properties of novel fullerene-functionalized halogen-bonding (XB) heteroditopic ion-pair receptors containing cation and anion binding domains spatially separated by C60. Fullerene spatial separation of the XB donors and the crown ether complexed potassium cation resulted in a rare example of an artificial receptor containing two anion binding sites with opposing preferences for hard and soft halides. Importantly, the incorporation of the C60 motif into the heteroditopic receptor structure has a significant effect on the halide binding selectivity, which is further amplified upon K+ cation binding. The potassium cation complexed fullerene-based receptors exhibit enhanced selectivity for the soft polarizable iodide ion which is assisted by the C60 scaffold preorganizing the potent XB-based binding domains, anion-π interactions, and the exceptional polarizability of the fullerene moiety, as evidenced from DFT calculations. These observations serve to highlight the unique properties of fullerene surfaces for proximal charged guest binding with potential applications in construction of selective molecular sensors and modulating the properties of solar cell devices.

Anion-π catalysis on carbon allotropes

Anion-π catalysis, introduced in 2013, stands for the stabilization of anionic transition states on π-acidic aromatic surfaces. Anion-π catalysis on carbon allotropes is particularly attractive because high polarizability promises access to really strong anion-π interactions. With these expectations, anion-π catalysis on fullerenes has been introduced in 2017, followed by carbon nanotubes in 2019. Consistent with expectations from theory, anion-π catalysis on carbon allotropes generally increases with polarizability. Realized examples reach from enolate addition chemistry to asymmetric Diels-Alder reactions and autocatalytic ether cyclizations. Currently, anion-π catalysis on carbon allotropes gains momentum because the combination with electric-field-assisted catalysis promises transformative impact on organic synthesis.

CH3 CN@open-C60 : An Effective Inner-Space Modification and Isotope Effect Inside a Nano-Sized Flask

Despite several small molecules being encapsulated inside cage-opened fullerene derivatives, such species have not considerably affected the structures and properties of the outer carbon cages. Herein, we achieved an effective inner-space modification for an open-cage C60 derivative by insertion of a neutral CH3 CN molecule into the cavity. The CH3 CN@open-C60 thus obtained showed an enhanced polarity, thus affording an easy separation from a mixture containing the empty cage by column chromatography on silica gel, without the preparative HPLC that was needed for previous cases. The less negative reduction potentials with respect to those of empty cage reflect the decreased energy level of the LUMO, which is supported by the DFT calculations. NMR spectroscopy, single-crystal X-ray analysis, and theoretical calculations revealed that both the presence of the encapsulated CH3 CN and cage deformation caused by the CH3 CN play an essential role in the change of the electronic properties. Furthermore, the favored binding affinity of deuterated acetonitrile CD3 CN with internal C60 surface is discussed.

[60]Fullerene-Fused Cyclopentanes: Mechanosynthesis and Photovoltaic Application

The mechanochemical cascade reaction of [60]fullerene with 3-benzylidene succinimides, diethyl 2-benzylidene succinate, or 2-benzylidene succinonitrile in the presence of an inorganic base has been investigated under solvent-free and ball-milling conditions. This protocol provides an expedient method to afford various [60]fullerene-fused cyclopentanes, showing advantages of good substrate scope, short reaction time, and solvent-free and ambient reaction conditions. Furthermore, representative fullerene products have been applied in inverted planar perovskite solar cells as efficient cathode interlayers.