Site-Specific Reduction-Induced Hydrogenation of a Helical Bilayer Nanographene with K and Rb Metals: Electron Multiaddition and Selective Rb+ Complexation

Abstract

The chemical reduction of π-conjugated bilayer nanographene 1 (C138H120) with K and Rb in the presence of 18-crown-6 affords [K+(18-crown-6)(THF)2][{K+(18-crown-6)}2(THF)0.5][C138H1223−] (2) and [Rb+(18-crown-6)2][{Rb+(18-crown-6)}2(C138H1223−)] (3). Whereas K+ cations are fully solvent-separated from the trianionic core thus affording a “naked” 1.3− anion, Rb+ cations are coordinated to the negatively charged layers of 1.3−. According to DFT calculations, the localization of the first two electrons in the helicene moiety leads to an unprecedented site-specific hydrogenation process at the carbon atoms located on the edge of the helicene backbone. This uncommon reduction-induced site-specific hydrogenation provokes dramatic changes in the (electronic) structure of 1 as the helicene backbone becomes more compressed and twisted upon chemical reduction, which results in a clear slippage of the bilayers.