Dearomative Ring‐Fused Azafulleroids and Carbazole‐Derived Metallofullerenes: Reactivity Dictated by Encapsulation in a Fullerene Cage

Abstract

Herein, we report divergent additions of 2,2′‐diazidobiphenyls to C60 and Sc3N@Ih‐C80. In stark contrast to that of the previously reported bis‐azide additions, the unexpected cascade reaction leads to the dearomative formation of azafulleroids 2 fused with a 7‐6‐5‐membered ring system in the case of C60. In contrast, the corresponding reaction with Sc3N@Ih‐C80 switches to the C−H insertion pathway, thereby resulting in multiple isomers, including a carbazole‐derived [6,6]‐azametallofulleroid 3 and a [5,6]‐azametallofulleroid 4 and an unusual 1,2,3,6‐tetrahydropyrrolo[3,2‐c]carbazole‐derived metallofullerene 5, whose molecular structures have been unambiguously determined by single‐crystal X‐ray diffraction analyses. Among them, the addition type of 5 is observed for the first time in all reported additions of azides to fullerenes. Furthermore, unexpected isomerizations from 3 to 5 and from 4 to 5 have been discovered, providing the first examples of the isomerization of an azafulleroid to a carbazole‐derived fullerene rather than an aziridinofullerene. In particular, the isomerism of the [5,6]‐isomer 4 to the [5,6]‐isomer 5 is unprecedented in fullerene chemistry, contradicting the present understanding that isomerization generally occurs between [5,6]‐ and [6,6]‐isomers. Control experiments have been carried out to rationalize the reaction mechanism. Furthermore, representative azafulleroids have been applied in organic solar cells, thereby resulting in improved power conversion efficiencies.