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Abstract The two‐fold reduction of tetrabenzo[a,c,e,g]cyclooctatetraene (TBCOT, or tetraphenylene,1) with K, Rb, and Cs metals reveals a distinctive core transformation pathway: a newly formed C−C bond converts the central eight‐membered ring into a twisted core with two fused five‐membered rings. This C−C bond of 1.589(3)–1.606(6) Å falls into a single σ‐bond range and generates two perpendicular π‐surfaces with dihedral angles of 110.3(9)°–117.4(1)° in the1TR2−dianions. As a result, the highly contorted1TR2−ligand exhibits a “butterfly” shape and could provide different coordination sites for metal‐ion binding. The K‐induced reduction of1in THF affords a polymeric product with low solubility, namely [{K+(THF)}2(1TR2−)] (K2‐1TR2−). The use of a secondary ligand facilitates the isolation of discrete complexes with heavy alkali metals, [Rb+(18‐crown‐6)]2[1TR2−] (Rb2‐1TR2−) and [Cs+(18‐crown‐6)]2[1TR2−] (Cs2‐1TR2−). Both internal and external coordination are observed inK2‐1TR2−, while the bulky 18‐crown‐6 ligand only allows external metal binding inRb2‐1TR2−andCs2‐1TR2−. The reversibility of the two‐fold reduction and bond rearrangement is demonstrated by NMR spectroscopy. Computational analysis shows that the heavier alkali metals enable effective charge transfer from the1TR2−TBCOT dianion, however, the aromaticity of the polycyclic ligand remains largely unaffected.
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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 nanographene1(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 of1.3−. 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 of1as the helicene backbone becomes more compressed and twisted upon chemical reduction, which results in a clear slippage of the bilayers.
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- PAR ID:
- 10364321
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 61
- Issue:
- 10
- ISSN:
- 1433-7851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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