Tuning Magnetic Interactions Between Triphenylene Radicals by Variation of Crystal Packing in Structures with Alkali Metal Counterions

Egger

et al. 2022

J. Am. Chem. Soc.

Self Cite

We describe reductive dehydrogenative cyclizations that form hepta-, nona-, and decacyclic anionic graphene subunits from mono-and bis-helicenes with an embedded five-membered ring. The reaction of bis-helicenes can either proceed to the full double annulation or be interrupted by addition of molecular oxygen at an intermediate stage. The regioselectivity of the interrupted cyclization cascade for bishelicenes confirms that relief of antiaromaticity is a dominant force for these facile ring closures. Computational analysis reveals the unique role of the preexisting negatively charged cyclopentadienyl moiety in directing the second negative charge at a specific remote location and, thus, creating a localized antiaromatic region. This region is the hotspot that promotes the initial cyclization. Computational studies, including MO analysis, molecular electrostatic potential maps, and NICS(1.7) ZZ calculations, evaluate the interplay of the various effects including charge delocalization, helicene strain release, and antiaromaticity. The role of antiaromaticity relief is further supported by efficient reductive closure of the less strained monohelicenes where the relief of antiaromaticity promotes the cyclization even when the strain is substantially reduced. The latter finding significantly expands the scope of this reductive alternative to the Scholl ring closure.

Section: Resultssupporting

confidence: 77%

“…Notably, an extra K···C contact (3.304(5) Å) found between the K + ion and the adjacent C 31 H 19 – monoanion results in the propagation of a one-dimensional polymeric chain in K + -2 – (Figure ). All K···C and K···O distances in K + -2 – are comparable to the reported values. − …”

Section: Resultsmentioning

confidence: 99%

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

Egger

et al. 2022

J. Am. Chem. Soc.

Self Cite

“…A comparison of two anionic sandwiches shows that the distance of the K + ion from the ring centroid in 4 is notably shorter (2.986(2) Å, Figure c) than that in 3 (3.023(7) Å, Figure c). Unlike our recently reported potassium salt of a triphenylene radical monoanion, all K–C and K–O distances are comparable to those previously reported. − …”

Section: Resultssupporting

confidence: 81%

Triply-Reduced Hexa-peri-hexabenzocoronenes: Solid-State Structures and Magnetic Properties

Crystal Growth & Design

Wei

Yao

et al. 2023

Self Cite

Discotic polycyclic aromatics have attracted great interest in both fundamental chemistry and material science due to their degenerate frontier orbitals, high molecular symmetry, unique solid-state packing, and ability to bear a certain number of unpaired electrons that can be applied in molecular spintronics and quantum computing. In this work, chemical reduction of hexa-perihexabenzocoronenes, HBC (1) and tBu-HBC (2), as "superbenzenes", has been investigated with K metal in THF solution. These reactions readily afforded the triply reduced HBC-based products which have been isolated as single-crystalline materials. The X-ray diffraction study confirmed the formation of π-complexes [K + (18-crown-6)(THF) 2 ][{K + (18-crown-6)} 2 (1 3− )] (3) and [K + (18-crown-6)(THF) 2 ][{K + (18-crown-6)} 2 (2 3− )] (4). In 3 and 4, two potassium ions were found to bind the central sixmembered rings of 1 3− and 2 3− with one potassium counterion remaining solvent-separated from the complexes. A notable geometry distortion of the HBC core upon three-electron acquisition and metal binding was revealed in both complexes. The presence of bulky substituents in 2 affected the coordination and crystal packing of otherwise similar building units in 4 vs 3. The magnetic properties of 4 supported the existence of a well-isolated S = 3/2 ground state of the 2 3− triradical in the solid state.

“…The coordination environment of each K + ion is completed by one 18-crown-6 ether molecule, with corresponding K•••O distances spanning over 2.755(4)-3.042(4) Å. All K•••C and K•••O distances are close to those previously reported [104][105][106].…”

supporting

confidence: 76%

“…All K•••C and K•••O distances in K + -2are comparable to the reported values. [104][105][106] In the crystal structure of (K + )2-2a 2-(Figure 7), the K1 ion binds to a six-membered ring of The distortion of the carbon framework during deprotonation and reduction steps was analyzed using selected torsion and dihedral angles (Table 4). After the site-selective In the solid-state structure of Cs + -2 -, a 3D network is formed through multiple C-H•••π interactions between the C31H19 − monoanions and the adjacent 18-crown-6 ether of the cationic moieties, with distances ranging from 2.605(5) Å to 2.809(5) Å (Figure 8).…”

Section: Crystal Structures Of the Anionic And Dianionic Products Fro...mentioning

confidence: 99%

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

Egger

et al. 2022

Preprint

We describe reductive dehydrogenative cyclizations that form hepta-, nona- and decacyclic anionic graphene subunits from mono- and bis-helicenes with an embedded five-membered ring. The reaction of bis-helicenes can either proceed to the full double annulation or be interrupted by addition of molecular oxygen at an intermediate stage. The regioselectivity of the interrupted cyclization cascade for bis-helicenes confirms that relief of antiaromaticity is a dominant force for these facile ring closures. Computational analysis reveals the unique role of the preexisting negatively charged cyclopentadienyl moiety in directing the 2nd negative charge at a specific remote location and, thus, creating a localized antiaromatic region. This region is the hot-spot that promotes the initial cyclization. Computational studies, including MO analysis, molecular electrostatic potential maps, and NICS(1.7)ZZ calculations evaluate the interplay of the various effects including charge delocalization, helicene strain release, and antiaromaticity. The role of antiaromaticity relief is further supported by efficient reductive closure of the less strained mono-helicenes where the relief of antiaromaticity promotes the cyclization even when the strain is substantially reduced. The latter finding significantly expands the scope of this reductive alternative to the Scholl ring closure.