Dearomative Ring‐Fused Azafulleroids and Carbazole‐Derived Metallofullerenes: Reactivity Dictated by Encapsulation in a Fullerene Cage
Tongxin Liu, Xin Wang, Shilu Xia, Muqing Chen, Mingjie Li, Panting Yang, Nana Ma, Ziqi Hu, Shangfeng Yang, Guisheng Zhang, Guan‐Wu Wang
Abstract
Abstract Herein, we report divergent additions of 2,2′‐diazidobiphenyls to C 60 and Sc 3 N@I h ‐C 80 . 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 C 60 . In contrast, the corresponding reaction with Sc 3 N@I h ‐C 80 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.