First Synthesis and Characterization of CH₄@C₆₀

Abstract

The endohedral fullerene CH 4 @C 60 ,i nw hich each C 60 fullerene cage encapsulates asingle methane molecule,has been synthesized for the first time.Methane is the first organic molecule,a swella st he largest, to have been encapsulated in C 60 to date.T he key orifice contraction step,aphotochemical desulfinylation of an open fullerene,w as completed, even though it is inhibited by the endohedral molecule.T he crystal structure of the nickel(II) octaethylporphyrin/ benzenesolvate shows no significant distortion of the carbon cage,r elative to the C 60 analogue,and shows the methane hydrogens as ashell of electron density around the central carbon, indicative of the quantum nature of the methane.The 1 Hspin-lattice relaxation times (T 1 )f or endohedral methane are similar to those observed in the gas phase,i ndicating that methane is freely rotating inside the C 60 cage.T he synthesis of CH 4 @C 60 opens ar oute to endofullerenes incorporating large guest molecules and atoms.Soon after the discovery of C 60 in 1985, [1] came recognition that its approximately spherical 3.7 diameter cavity provides aunique environment in which to isolate single atoms. [2] Since then endohedral fullerenes,that is,compounds denoted A@C 60 in which molecules or atoms are enclosed within the fullerene cage,have been the focus of substantial experimental and theoretical efforts. [3][4][5] Endohedral fullerenes may be synthesized by forming the fullerene in the presence of the endohedral species (particularly successful for metallofullerenes), [3,5] by high temperature and pressure treatment of the fullerene with the endohedral species (inert gas@C 60 ), [6,7] or by ion bombardment of the fullerene (N@C 60 ), [8] but all give very low incorporation and require extensive purification. Furthermore,t hese methods are not applicable to the incorporation of small organic molecules.Them acroscopic-scale preparation of endohedral fullerenes by multi-step "molecular surgery" [9][10][11][12] involves chemically opening an orifice in the fullerene,o fas ize suitable to allow entry of the single molecule.S uturing of this orifice to restore the pristine carbon cage was pioneered by Komatsu [13,14] and Murata [15] who reported the first syntheses of H 2 @C 60 and H 2 O@C 60 following insertion of H 2 or H 2 O under high-pressure,i nto open-cage fullerenes 1 and 2, respectively.O ptimized procedures for the synthesis of H 2 @C 60 and H 2 O@C 60 have subsequently been reported by ourselves, [16] based on Murataso pen-cage C 60 derivative 2, and also applied to the synthesis of HF@C 60 (Figure 1). [17,18] Them acroscopic quantities of endohedral fullerenes provided by molecular surgery have allowed detailed investigation of physical properties,i ncluding by neutron scattering, infrared spectroscopy,a nd NMR spectroscopy. [19] These methods have shown that, as ar esult of the inert and highly symmetrical environment of the cavity,a ne ntrapped molecule behaves much as would be expected in the very lowpressure gas state, [17,[19][20][21][22][23] displ...

Encapsulation of a Water Molecule inside C60 Fullerene: The Impact of Confinement on Quantum Features

“…A step advance in endofullerene science has been made with the advent of a novel, multistep organic synthesis procedure known as molecular surgery. 9 − 12 , 29 , 32 − 34 Such a procedure consists of a series of chemical reactions for creating an open C 60 cage, in which the guest molecule can be inserted, followed by the closing of the cage with the guest trapped inside. Various molecules, such as H 2 , HD, HF, H 2 O, and CH 4 , have been encapsulated into C 60 in this manner to date, and their properties have been experimentally investigated by X-ray diffraction, inelastic neutron scattering (INS), far-infrared spectroscopy (FIR), and nuclear magnetic resonance (NMR) spectroscopy techniques.…”

EPR study of NO radicals encased in modified open C<sub>60</sub> fullerenes

“…Using such designertype open cages instead of closed structures creates a new route for the preparation of interesting compounds. The family of endohedral fullerenes with closed carbon cages like N@C 60 (Murphy et al, 1996), He@C 60 (Saunders et al, 1994), H 2 @C 60 (Komatsu et al, 2005), H 2 O@C 60 (Kurotobi and Murata, 2011), HF@C 60 (Krachmalnicoff et al, 2016), and CH 4 @C 60 (Bloodworth et al, 2019), as well as C 82 (Stevenson et al, 1999) based metallo-endohedrals, can thus be expanded significantly. It has been shown that these new compounds can be stable under ambient conditions, allowing easy handling.…”

The Endofullerene HF@C60: Inelastic Neutron Scattering Spectra from Quantum Simulations and Experiment, Validity of the Selection Rule, and Symmetry Breaking

“…1,2 Their synthesis has been accomplished utilizing the approach known as molecular surgery, in which a hole is created in the fullerene cage through a sequence of chemical reactions allowing the insertion of the guest molecule into the cavity, followed by reforming the pristine fullerene shell with the guest molecule trapped in its interior. [3][4][5][6] Inside C 60 , the entrapped molecules are under the conditions unlike any other studied previouslyconfined in the highly symmetric and nonpolar nanoscale cage and, in the case of HF and H 2 O, isolated and unable to form hydrogen bonds to other molecules.…”