Supramolecular Fullerene Sponges As Catalytic Masks for Regioselective Functionalization of C <sub>60</sub>

Abstract

Isomer-pure poly-functionalizalized fullerenes are required to boost the development of fullerene chemistry in any field, and specifically in solar cell design. Easy-accessible mono-functionalized fullerenes are mainly used in organic- or perovskite-based solar cells, due to the hampered accessibility to pure-isomer poly-adduct derivatives. In a general basis, multi-adduct mixtures with uncontrolled regioselectivity are obtained, and chromatographic purification is prohibitively costly and time-consuming to be used in the production of solar cells. Moreover, single isomer poly-functionalized fullerenes are only accessible via stoichiometric, multistep paths entailing protecting-unprotecting sequences. Herein, a nanocapsule is used as a supramolecular mask to exert full control on the reactivity and the equatorial regioselectivity of Bingel-Hirsch cyclopropanation reactions of confined fullerene guests. Thus, equatorial bis-, tris- and tetrakis-C60 homo-adducts are exclusively obtained in a stepwise manner, completely avoiding over functionalization (always observed in bulk solution) and holding precise control on the number of additions. Regioselectivity is strictly dictated by the four cross-shaped open windows in the tetragonal prismatic supramolecular container. Furthermore, isomer-pure equatorial hetero-tetrakis-adducts or hetero-Th-hexakis-adducts are synthesized at will in one-pot synthesis for the first time. Remarkably, a synthetically useful biphasic protocol is designed to achieve selective and quantitative formation of exclusively tetrakis-adducts using catalytic amounts of nanocapsule. Therefore, the confinement control imposed by the capsule’s cavity conforms a unique practical strategy to infer regio-control to the synthesis of fullerene equatorial poly-adducts. This work provides a synthetically valuable path to produce a plethora of new pure-isomer poly-functionalized C60-based compounds, as candidates for testing in solar cell devices and for biomedical applications.