Unexpected Formation of Pyrazoline-Fused Metallofullerenes from the Multicomponent Cascade Reaction of Sc3N@Ih-C80 with Tetrazines, Water, and Oxygen

Inverse Electron Demand Diels-Alder Reaction on M3N@C80 (M=Lu, Sc): Reactivity and Reversibility Enable Chemical Separation of Metallofullerenes

Endohedral metallofullerenes are chemically more inert compared to empty fullerenes, primarily due to their intramolecular electron transfer. In this work, we report an inverse electron demand Diels-Alder (IEDDA) reaction on M3N@C80 (M=Lu, Sc), where they show significantly higher reactivity than empty fullerenes. The molecular structures of the [4+2] cycloadducts were unambiguously characterized. Moreover, the cycloadducts can fully revert to pristine M3N@C80 via retro-cycloaddition upon thermal treatment. With the unusual reactivity and reversibility, the IEDDA reaction enables an effective separation approach for metallofullerenes from their soot extracts, opening path to efficient and economical scale-up synthesis of metallofullerenes in laboratory and industrial settings.

Effects of Solvents on Reaction Products: Synthesis of Endohedral Metallofullerene Oxazoline and Epoxide

Herein, we performed the reactions of M₃N@I_h-C₈₀ (M = Sc and Lu) with the methanol (CH₃OH) solution of TBAOH (note that both CH₃O^- and OH^- are nucleophiles) in benzonitrile (PhCN) and dimethylformamide, respectively. It is found that OH^- ions rather than CH₃O^- ions selectively attacked the fullerene cage to form the M₃N@C₈₀^--O^- intermediate. Although the fullerene cage is initially attacked by OH^- in both PhCN and DMF solvents, the products are quite different. In PhCN, two isomeric Sc₃N@I_h-C₈₀ fullerooxazoline heterocyclic products (1 and 2) were synthesized. Whereas, in DMF, an epoxide of Lu₃N@I_h-C₈₀ (3) was obtained. The preference for fullerooxazoline formation over that of fullerene epoxy in PhCN is well explained by density functional theory calculations. Plausible reaction mechanisms for the formation of metallofullerene oxazoline and epoxide were proposed based on the experimental and theoretical results.

[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.

Synthesis of [60]- and [70]Fullerene-Fused Tetrahydroquinoxaline Derivatives by Oxidative [4 + 2] Cycloaddition with Unusual Reactivity and Regioselectivity

The oxidative [4 + 2] reaction of o-phenylenediamine-derived disulfonamides with fullerene C₆₀ and C₇₀ is reported, in which electron-deficient reactants showed high reactivity. The reaction of C₇₀ exhibited unusual regioselectivity, yielding a [5,6]-adduct as the major product, which was characterized by ¹H, ¹³C NMR and single-crystal X-ray diffraction. DFT calculations revealed the reaction is an inverse-electron-demand Diels-Alder (IEDDA) reaction, and the [5,6]-adduct of C₇₀ is a kinetic product.