Stepwise Generation of Mono‐, Di‐, and Triply‐Reduced Warped Nanographenes: Charge‐Dependent Aromaticity, Surface Nonequivalence, Swing Distortion, and Metal Binding Sites

• Published in: Angewandte Chemie International Edition 2021-11, Vol.60 (48), p.25445-25453
• Main Authors: Spisak, Sarah N., Zhou, Zheng, Liu, Shuyang, Xu, Qi, Wei, Zheng, Kato, Kenta, Segawa, Yasutomo, Itami, Kenichiro, Rogachev, Andrey Yu, Petrukhina, Marina A.
• Format: Article
• Language: English
• Subjects: Aromaticity; Binding sites; cesium; Cesium ions; Chemical reduction; Computer applications; Crystallography; DFT calculations; Electronic structure; Electrostatic properties; Localization; nanographenes; Software; Structural analysis; Surface charge; X-ray crystallography
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202110748

The stepwise chemical reduction of a molecular warped nanographene (WNG) having a negatively curved π‐surface and defined C80H30 composition with Cs metal used as the reducing and complexing agent allowed the isolation of three different reduced states with one, two, and three electrons added to its π‐conjugated system. This provided a unique series of nanosized carbanions with increasing negative charge for in‐depth structural analysis of consequences of controlled electron charging of non‐planar nanographenes, using X‐ray crystallographic and computational tools. The 3D molecular electrostatic potential (MEP) maps identified the negative charge localization at the central part of the WNG surface where selective coordination of Cs+ ions is confirmed crystallographically. In‐depth theoretical investigation revealed a complex response of the WNG to the stepwise electron acquisition. The extended and contorted π‐surface of the WNG undergoes subtle swinging distortions that are accompanied by notable changes in the electronic structure and site‐dependent aromaticity of the resulting carbanions. Stepwise chemical reduction of a molecular warped nanographene (WNG, 1) with Cs metal affords the mono‐, di‐, and triply‐reduced nanosized carbanions. In‐depth X‐ray crystallographic analysis and comprehensive theoretical investigations of this series of negatively charged nanographenes reveal a very complex response and core flexibility upon multi‐electron charging.