Long-Lived C Radical Anion Stabilized Inside an Electron-Deficient Coordination Cage.

Fullerene C and its derivatives are widely used in molecular electronics, photovoltaics, and battery materials, because of their exceptional suitability as electron acceptors. In this context, single-electron transfer on C generates the C radical anion. However, the short lifetime of free C hampers its investigation and application. In this work, we dramatically stabilize the usually short-lived C species within a self-assembled ML coordination cage consisting of a triptycene-based ligand and Pd(II) cations. The electron-deficient cage strongly binds C by providing a curved inner π-surface complementary to the fullerene's globular shape. Cyclic voltammetry revealed a positive potential shift for the first reduction of encapsulated C, which is indicative of a strong interaction between confined C and the cationic cage. Photochemical one-electron reduction with 1-benzyl-1,4-dihydronicotinamide allows selective and quantitative conversion of the confined C molecule in millimolar acetonitrile solution at room temperature. Radical generation was confirmed by nuclear magnetic resonance, electron paramagnetic resonance, ultraviolet-visible-near-infrared spectroscopy and electrospray ionization mass spectrometry. The lifetime of C within the cage was determined to be so large that it could still be detected after one month under an inert atmosphere.