The Structure of a Seven-Bladed Propeller: C7Ph7+ is Not Planar

Brydges, Stacey; Britten, James F.; Chao, Lisa C. F.; Gupta, Hari K.; McGlinchey, Michael J.; Pole, David L.

doi:10.1002/(sici)1521-3765(19980710)4:7<1201::aid-chem1201>3.0.co;2-y

Cited by 24 publications

(25 citation statements)

References 11 publications

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“…In continuation of our long-term study of sterically very hindered organometallic or organic molecules that might function as molecular propellers or gears, we had prepared [(η 6 -C 6 Et 6 )Cr(CO)(CS)NO] + [1], (η 5 -C 5 Ph 5 )Fe(CO)(HC=O)PMe 2 Ph [2], ferrocenyl-pentanaphthylbenzene [3], [C 7 Ph 7 ] + [4], 9-triptycyl-indenyl dimer [5], and numerous others.…”

Section: Introductionmentioning

confidence: 99%

From allenes to tetracenes: Syntheses, structures, and reactivity of the intermediates

Banide

Oulié

McGlinchey

2009

Pure and Applied Chemistry

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Each step of the conversion of a series of 9-alkynyl-9H-fluorenes into the corresponding fluorenylidene-allenes that dimerize and proceed sequentially via head-to-tail and tail-to-tail dialkylidene-cyclobutanes, en route to electroluminescent tetracenes, has been characterized X-ray crystallographically. Allenes possessing substituents of very different electronic and steric character, such as aryl, halogeno, silyl, phosphino, and ferrocenyl, exhibit novel and unexpected reactivity patterns. The silyl-allenes dimerize to yield 1,2-bis(fluorenylidene)cyclobutanes of intrinsic C 2 symmetry as a result of the overlapping fluorenylidenes with their large wingspans. Thermal rearrangement of a bis(fluorenyl)bis(trimethylsilyl)-diallene generates the tetrabenzo-quatercyclopentadiene, C 60 H 36 , which represents 60 % of the C 60 framework. An attempt to isolate a "push-pull" allene, whose central carbon possesses carbene character, was made by incorporating a cation-stabilizing substituent (ferrocenyl) and an aromatic anionic moiety (fluorenide) at the termini. However, the allene underwent facile dimerization to the very heavily congested 3,4-di(spirofluorenyl)-1,2-bis(ferrocenyl-chloromethylene)cyclobutane that exhibits a very long (1.65 Å) C(3)-C(4) bond. Extension of this chemistry to dibenzosuberenylidene-allenes led to a straightforward route to the hitherto difficultly available dibenz[c,d,h]azulene system. Moreover, the reaction of 5-phenylethynyl-5H-dibenzo[a,d]cyclohepten-5-ol with dicobalt octacarbonyl yielded, surprisingly, the first isolated example of a (µ-alkyne)Co 2 (CO) 5 (η 2 -alkene)complex, the long-sought first intermediate in the proposed mechanism of the Pauson-Khand reaction (PKR).

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Section: Introductionmentioning

confidence: 99%

From allenes to tetracenes: Syntheses, structures, and reactivity of the intermediates

Banide

Oulié

McGlinchey

2009

Pure and Applied Chemistry

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“…In continuation of our work on sterically hindered organic and organometallic systems, such as C 7 Ph 7 + , [(C 6 Et 6 )Cr(CO)(CS)(NO)] + , (C 6 Ph 6 )Cr(CO) 3 , rhodium and iron complexes of naphthyl‐substituted cyclopentadionones, and indenyl and ferrocenyl derivatives of anthracene and triptycene, we chose to prepare 5 with a view to elucidating its structure and dynamic behaviour. The route depicted in Scheme involved treatment of β‐naphthil dihydrazone, 1 , with silver oxide to produce di(β‐naphthyl)acetylene, 2 , in 91 % yield.…”

Section: Resultsmentioning

confidence: 99%

A Synthetic, X‐ray, NMR Spectroscopy and DFT Study of β‐Naphthil Dihydrazone, Di(β‐naphthyl)acetylene, Tetra(β‐naphthyl)cyclopentadienone, and Hexa(β‐naphthyl)‐benzene: C₆(C₁₀H₇)₆ Is a Disordered Molecular Propeller

et al. 2017

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Treatment of β‐naphthil dihydrazone, 1, with silver oxide yields di(β‐naphthyl)acetylene, 2, which undergoes Diels–Alder cycloaddition with tetra(β‐naphthyl)cyclopentadienone, 4, to give hexa(β‐naphthyl)benzene, 5, upon decarbonylation. Molecules 1, 2 and 4 have been characterised by X‐ray crystallography, but hexa(β‐naphthyl)benzene exhibits rotational disorder of the peripheral substituents. Nevertheless, calculations at the density functional level reveal the favoured structure of 5 to be a molecular propeller, in which the eight possible rotamers are essentially iso‐energetic. Variable‐temperature NMR spectroscopy studies yield a naphthyl rotational barrier of approximately 17 kcal mol−1, similar to that previously found for meta‐substituted phenyl groups. Enantiomerisation of hexa(β‐naphthyl)benzene engendered by rotation of a single naphthyl ring has been studied by DFT calculations, and the process has been represented pictorially.

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“…60° for benzene) allow tropylium to undergo more facile strain-induced deformations. 17,18 Consequently, it has the potential to form highly twisted structures and to serve as a versatile subunit to probe aromaticity in geometrically deformed systems. 19 In recent years, there has been increasing interest in aromatic structures that are nonplanar, including helicenes, 20 twistacenes, 21,22 Möbius aromatics, 23,24 nanohoops, [25][26][27] nanobelts, 28,29 and warped nanographenes.…”

Section: Introductionmentioning

confidence: 99%

Rupturing Aromaticity by Periphery Overcrowding

Saha

Mallick

Turley

et al. 2022

Preprint

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The balance between strain relief and aromatic stabilization dictates the form and function of nonplanar π-aromatics. Overcrowded systems undergo geometric deformations, but the energetically favourable π-electron delocalization of their aromatic ring(s) is typically preserved. Here, we use peripheral overcrowding to increment the strain energy of an aromatic system beyond its aromatic stabilization energy, causing the ring system to rearrange and aromaticity to be ruptured. Firstly, increasing steric bulk around the periphery of π-extended tropylium ring systems leads them to deviate from planarity. We observe contorted conformations with end-to-end twists of up to 45.2°. Aromatic stabilization and strain energies are closely matched at this critical point. Upon further increasing the strain, the aromatic π-electron delocalization of the system is broken—the aromatic tropylium ring rearranges to a nonaromatic, bicyclic analogue, ‘Dewar tropylium’. Remarkably, by counterbalancing strain against aromatic stabilization energy, we observe that these aromatic and nonaromatic isomers can exist in equilibrium with one another. Dynamic NMR measurements reveal that the isomers interconvert rapidly. This investigation of the antagonistic relationship between aromaticity and strain provides direct experimental insights into the fundamental nature of aromaticity and demarcates the extent of steric deformation tolerated by an aromatic carbocycle.

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The Structure of a Seven-Bladed Propeller: C7Ph7+ is Not Planar

Cited by 24 publications

References 11 publications

From allenes to tetracenes: Syntheses, structures, and reactivity of the intermediates

From allenes to tetracenes: Syntheses, structures, and reactivity of the intermediates

A Synthetic, X‐ray, NMR Spectroscopy and DFT Study of β‐Naphthil Dihydrazone, Di(β‐naphthyl)acetylene, Tetra(β‐naphthyl)cyclopentadienone, and Hexa(β‐naphthyl)‐benzene: C₆(C₁₀H₇)₆ Is a Disordered Molecular Propeller

Rupturing Aromaticity by Periphery Overcrowding

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The Structure of a Seven-Bladed Propeller: C7Ph7+ is Not Planar

Cited by 24 publications

References 11 publications

From allenes to tetracenes: Syntheses, structures, and reactivity of the intermediates

From allenes to tetracenes: Syntheses, structures, and reactivity of the intermediates

A Synthetic, X‐ray, NMR Spectroscopy and DFT Study of β‐Naphthil Dihydrazone, Di(β‐naphthyl)acetylene, Tetra(β‐naphthyl)cyclopentadienone, and Hexa(β‐naphthyl)‐benzene: C6(C10H7)6 Is a Disordered Molecular Propeller

Rupturing Aromaticity by Periphery Overcrowding

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A Synthetic, X‐ray, NMR Spectroscopy and DFT Study of β‐Naphthil Dihydrazone, Di(β‐naphthyl)acetylene, Tetra(β‐naphthyl)cyclopentadienone, and Hexa(β‐naphthyl)‐benzene: C₆(C₁₀H₇)₆ Is a Disordered Molecular Propeller