Search for: All records

Abstract The chemical reduction of a bilayer spironanographene,spiro‐NG(C₁₃₇H₁₂₀), with Na and K metals in the presence of [2.2.2]cryptand to yield [Na⁺(2.2.2‐cryptand)](C₁₃₇H₁₂₁⁻) (1) and [K⁺(2.2.2‐cryptand)](C₁₃₇H₁₂₁⁻) (2), respectively, is reported. X‐ray crystallography reveals the formation of a new “naked” anion (spiro‐NG_H⁻), in which spirocyclic ring cleavage and subsequent hydrogenation have occurred. Density Functional Theory (DFT) calculations suggest that the generation of the radical anion of the parent nanographene (spiro‐NG^•−), upon electron acceptance from Na and K metals, induces the cleavage of the strained spirobifluorene core. The resulting spin density localizes on a particular carbon atom, previously attached to the spiranic sp³carbon atom, facilitating a site‐specific hydrogenation to afford (spiro‐NG_H⁻). The electrostatic potential map of this anion reveals electron density concentrated at the five‐membered ring of the readily formed indenyl fragment, thus enhancing the aromaticity of the system. Furthermore, nuclear magnetic resonance (NMR) and UV–vis absorption spectroscopy experiments allowed to follow the in situ reduction and hydrogenation processes in detail. 

“Redox Properties of Nanographenes”, Y. Zhu, M. A. Petrukhina. Chapter 20 in “Molecular Nanographenes: Synthesis, Properties and Applications”, Edited by N. Martín and C. Nuckols, Wiley-VCH, 2025, 449-482 

An overview of structural responses of helicenes with increasing dimensions and complexity to stepwise electron addition reveals charge- and topology-dependent outcomes ranging from reversible to irreversible core transformations and site-specific reactivity. 

The stepwise reduction by 1–3 electrons of a π-expanded pyracylene with K and Rb reveals that in-build core asymmetry affects the spin-density distribution in the mono- and trianion radicals, as confirmed by EPR spectroscopy and DFT calculations. 

Two-fold reduction of a vertically expanded functionalized pentacene with Na metal is accompanied by a loss of diatropicity in the resulting dianion and engagement of side groups in sodium ion coordination. 

A unique trimeric radical cation with unequal charge distribution is obtained by chemical oxidation of triphenylene with GaCl₃. XRD determined structure is combined with computational modeling showing stabilizing pancake bonding in the π-stacks. 

Abstract π-Conjugated macrocycles behave differently from analogous linear chains because their electronic wavefunctions resemble a quantum particle on a ring, leading to aromaticity or anti-aromaticity. [18]Annulene, (CH)₁₈, is the archetypal non-benzenoid aromatic hydrocarbon. Molecules with circuits of 4n + 2 π electrons, such as [18]annulene (n = 4), are aromatic, with enhanced stability and diatropic ring currents (magnetic shielding inside the ring), whereas those with 4nπ electrons, such as the dianion of [18]annulene, are expected to be anti-aromatic and exhibit the opposite behaviour. Here we use¹H NMR spectroscopy to re-evaluate the structure of the [18]annulene dianion. We also show that it can be reduced further to an aromatic tetraanion, which has the same shape as the dianion. The crystal structure of the tetraanion lithium salt confirms its geometry and reveals a metallocene-like sandwich, with five Li⁺cations intercalated between two [18]annulene tetraanions. We also report a heteroleptic sandwich, with [18]annulene and corannulene tetraanion decks. 

Anionic forms of a macrocyclic cyclophane were crystallized by treating the neutral hydrocarbon with alkali metals (Li, Na and K). The di-anions show decreased bond-length alternation, consistent with global aromaticity, whereas the anti-aromatic tetra-anion has a low-symmetry geometry.