Exohedral functionalization of endohedral metallofullerenes: Interplay between inside and outside

Endohedral metallofullerenes (EMFs) are fullerene cages enclosing various metallic species. The functionalization of EMFs has remarkably blossomed in recent years, in contrast to early efforts that were mainly devoted to their geometric and electronic structures as well as optical and magnetic properties. This review presents an exhaustive survey of the important functionalization approaches of EMFs, mainly focusing on the progress since 2014. The involved reactions include silylation and germylation, Diels–Alder reaction, Bingel–Hirsch reaction, 1,3-dipolar cycloaddition, carbene addition, benzyne addition, free radical reaction, hydroxylation, dimerization, coordination reaction, noncovalent complexation, as well as numerous miscellaneous reactions. We summarize the main factors that affect the reactivity and regioselectivity, focusing particularly on the intriguing interplay between the exohedral groups and internal species. This work highlights the established role of current theoretical studies in further understanding the reactivity and regioselectivity of functionalization reactions. Finally, we discuss potential applications of exohedrally modified EMFs.