Long-Lived C₆₀ Radical Anion Stabilized Inside an Electron-Deficient Coordination Cage

Abstract

Fullerene C 60 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 60 generates the C 60 • − radical anion. However, the short lifetime of free C 60• − hampers its investigation and application. In this work, we dramatically stabilize the usually short-lived C 60• − species within a self-assembled M 2 L 4 coordination cage consisting of a triptycene-based ligand and Pd(II) cations. The electron-deficient cage strongly binds C 60 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 60 , which is indicative of a strong interaction between confined C 60• − and the cationic cage. Photochemical one-electron reduction with 1benzyl-1,4-dihydronicotinamide allows selective and quantitative conversion of the confined C 60 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 60• − within the cage was determined to be so large that it could still be detected after one month under an inert atmosphere.

Porphyrin-Based Multicomponent Metallacage: Host–Guest Complexation toward Photooxidation-Triggered Reversible Encapsulation and Release

“…Compared with two-dimensional metallacycles, metallacages possess three-dimensional structures and cavities, making them encapsulate guest molecules from multiple directions and thus offering host–guest complexes with high binding affinities. 45 , 46 Therefore, during the past three decades, various metallacages have been extensively investigated and applied for guest encapsulation, 47 − 49 catalysis, 50 − 53 stabilizing reactive intermediates, 54 , 55 etc. Among them, porphyrin-based metallacages 56 , 57 have received much attention because they integrate the interesting optical and redox abilities of porphyrins and the host–guest properties of metallacages, offering extra functionalization such as light-harvesting and biological catalysis.…”

Artificial Metal–Peptide Assemblies: Bioinspired Assembly of Peptides and Metals through Space and across Length Scales

“…Metallo-supramolecular chemistry, pioneered by Fujita − and Stang, − has become a mature research field in the past two decades. The powerful strategy of metal-mediated self-assembly has enabled the construction of a large variety of structurally well-defined molecular architectures with uniquely functional nanospaces. ,, They have been put through studies in various applications such as host–guest recognition, − molecular adsorption and separation, − catalysis, − biological applications, − etc. However, because of the challenges in introducing guest-adaptive feature into these supramolecular coordination complexes, their abilities in biomolecular recognition are highly ineffective compared to natural systems.…”

Metal–organic cages against toxic chemicals and pollutants

“…Three-dimensional MOCs -also referred to as metal-organic polyhedra (MOP), coordination cages, or capsules -are a notable class of molecular assembled receptors that are formed as thermodynamically favoured products from the organisation of metal ions and organic ligands. 10,11 They have been widely used in molecular recognition, [12][13][14] stabilisation [15][16][17] and protection 18,19 of reactive species, chemical sensing, [20][21][22] gas adsorption, 23 molecular separation, [24][25][26] drug delivery, [27][28][29] bioimaging [30][31][32] as well as the exploration of new reactivity 33,34 and catalysis pathways. [35][36][37][38][39][40] As opposed to MOFs, defined only in the solid state, MOCs can be solubilised in common organic solvents and water, thereby facilitating their processing into support materials, and allowing inclusion complexes and catalytic phenomena to be observed in solution.…”