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Recently, mechanical milling using a mixer mill or planetary mill has been fruitfully utilized in organic synthesis under solvent-free conditions. This review article provides a comprehensive overview of various solvent-free mechanochemical organic reactions, including metal-mediated or -catalyzed reactions, condensation reactions, nucleophilic additions, cascade reactions, Diels-Alder reactions, oxidations, reductions, halogenation/aminohalogenation, etc. The ball milling technique has also been applied to the synthesis of calixarenes, rotaxanes and cage compounds, asymmetric synthesis as well as the transformation of biologically active compounds.

The bulk synthesis of the [2 + 2] dimer of fullerene C 60 was achieved by the solid-state mechanochemical reaction of C 60 with KCN by the use of a high-speed vibration milling (HSVM) technique. This reaction took place also by the use of potassium salts such as K 2 CO 3 and CH 3 -CO 2 K, metals such as Li, Na, K, Mg, Al, and Zn, and organic bases such as 4-(dimethylamino)-and 4-aminopyridine. Under optimum conditions, the reaction afforded only the dimer C 120 and unchanged C 60 in a ratio of about 3:7 (by weight) regardless of the reagent used. The dimer C 120 was fully characterized by IR, UV-vis, 13 C NMR, and TOF MS spectroscopies, cyclic voltammetry, and differential scanning calorimetry. Comparison of the IR and 13 C NMR spectral data of C 120 with those reported for all-carbon C 60 polymers implied that the [2 + 2] dimer C 120 represents the essential subunit of these polymers. The dimer C 120 underwent facile dissociation into two C 60 molecules by heat, HSVM treatment, exposure to room light, or electrochemical reduction. The dimer C 120 encapsulating 3 He in one of the C 60 cages was synthesized and was used to confirm the scrambling of a C 60 cage between the monomer and the dimer during the HSVM reaction. A possible mechanism for the selective formation of the dimer C 120 is proposed.

The cover picture shows the process of hydrogen and helium insertion/expulsion which has been achieved for the first time with an open fullerene derivative (outlined in the background). The experimental activation barrier for helium decomplexation could be obtained and fully agrees with the calculated value (density functional theory). The barrier for H2 complexation/decomplexation is interestingly almost double that of helium, as illustrated by the energy diagram shown in the foreground. This difference arises from the larger, elongated surface of H2 undergoing greater van der Waals interaction at the transition state relative to that of helium, even though both atoms have the same radii. More about this process can be found in the article by Rubin, Houk, Saunders, Cross et al. on p. 1543 ff.

The low or lack of solubility of fullerenes, carbon nanotubes and graphene/graphite in organic solvents and water severely hampers the study of their chemical functionalizations and practical applications. Covalent and noncovalent functionalizations of fullerenes and related materials via mechanochemistry seem appealing to tackle these problems. In this review article, we provide a comprehensive coverage on the mechanochemical reactions of fullerenes, carbon nanotubes and graphite, including dimerizations and trimerizations, nucleophilic additions, 1,3-dipolar cycloadditions, Diels-Alder reactions, [2 + 1] cycloadditions of carbenes and nitrenes, radical additions, oxidations, etc. It is intriguing to find that some reactions of fullerenes can only proceed under solvent-free conditions or undergo different reaction pathways from those of the liquid-phase counterparts to generate completely different products. We also present the application of the mechanical milling technique to complex formation, nanocomposite formation and enhanced hydrogen storage of carbon-related materials.

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Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

We report a new kind of experimental realization of a molecular rectifier, which is based on a single azafullerene C59N molecule in a double-barrier tunnel junction via the single electron tunneling effect. An obvious rectifying effect is observed. The positive onset voltage is about 0.5-0.7 V, while the negative onset voltage is about 1.6-1.8 V. Theoretical analyses show that the half-occupied molecular orbital of the C59N molecule and the asymmetric shift of the molecular Fermi level when the molecule is charged are responsible for the molecular rectification.