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

The chemical reduction of π-conjugated bilayer nanographene 1 (C H ) with K and Rb in the presence of 18-crown-6 affords [K (18-crown-6)(THF) ][{K (18-crown-6)} (THF) ][C H ] (2) and [Rb (18-crown-6) ][{Rb (18-crown-6)} (C H )] (3). Whereas K cations are fully solvent-separated from the trianionic core thus affording a "naked" 1 anion, Rb cations are coordinated to the negatively charged layers of 1 . 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.