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.

Localized Antiaromaticity Hotspot Drives Reductive Dehydrogenative Cyclizations in Bis- and Mono-Helicenes

“…The properties of helicenes can be also affected by "defects", such as variations in the ring size, 36,74−79 the presence of heteroatoms, 80−90 and multielectron addition. 17,91 Strain is an intrinsic property of helicenes and presents an additional challenge in their synthesis. In order to overcome this challenge, one needs to start with high-energy precursors.…”

“…In the crystal structure of Cs + -1 r − (Figure 2), the Cs + ion is sandwiched by two 18crown-6 ether molecules, with the Cs•••O distances ranging from 3.219(13) to 3.445(15) Å. 102,17 The cationic {Cs + (18crown-6) 2 } moiety is solvent-separated from the In the solid-state structure of Cs + -1 r − , a 2D layer is formed through C−H•••π interactions between the C 39 H 21 − monoanions and the adjacent 18-crown-6 ether molecules, with shortest distances ranging from 2.673(18) Å to 2.831(18) Å (Figure 3). No significant interactions were found between the adjacent layers.…”

Nanographenes and Graphene Nanoribbons as Multitalents of Present and Future Materials Science

“…Besides the Scholl reaction, the transition-metal-catalyzed [2 + 2 + 2] cycloaddition is another powerful tool to synthesize helical NGs. , The π-extended helicenes, sometimes referred to as superhelicenes, possess intriguing mechanical, electronic, magnetic, and spin properties as nanosprings and nanosolenoids . In addition to the neutral π-extended helicenes, the charged species obtained through metal reduction offer new possibilities to engineer the geometry, aromaticity, and electronic structures. − …”