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

Abstract

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.

Synthesis and characterization of propeller-shaped mono- to hexacationic quinolinium-substituted benzenes

“…34 It is known that methyl and methoxy groups in C 6 Ar 6 systems in ortho position cause a barrier of rotation of approximately 33 kcal mol −1 , whereas this value is considerably decreased to approximately 17 kcal mol −1 for the case of meta-substitutions. 23 Hexaphenylbenzene C 6 Ph 6 consequently displays one set of signals in the 13 C NMR spectra and one overlapped signal with a center of gravity at 6.83 ppm (30H) in the proton resonance spectra. 35 The chemical shifts of 10a-c are different as a consequence of their isomerism and, in addition, intermolecular interactions (Fig.…”

“…Theoretically, the salt 25 can exist in eight rotameric forms A-H. Similar to hexa(β-naphthyl)benzene, 23 solving the simple combinatoric problem created by propeller-like compounds such as 21 or 25 results in the following ratio: A : B : C : D : E : F : G : H = 1 : 6 : 3 : 6 : 6 : 3 : 6 : 1. Fig.…”

“…Recently, the sterically congested hexa(heteroaryl)benzene (HHAB) 4 was formed as two isolable isomers which differ only in the rotation of one methyl-pyridine group. 22 In general, propeller-shaped hexaarylbenzenes (HABs) such as hexa(β-naphthyl)benzene 5 23 have numerous applications in materials sciences as they play roles as liquid crystals, 24 microporous organic solids, 25 molecular capsules, 26 supramolecular electronic materials, 27 molecular rotors, 28 nonlinear optical materials, 29 metal sensors, 30 redox materials, 31 and molecular wires. 32 We report here on quinolinium-substituted benzenes which combine the features of HHABs and polycations as they have to adopt propeller-shaped…”

Diels-Alder Additions as Mechanistic Probes–Interception of Silyl-Isoindenes: Organometallic Derivatives of Polyphenylated Cycloheptatrienes and Related Seven-Membered Rings

“…The analogous naphthyl-substituted systems, tetra(β-naphthyl)cyclopentadienone, 26 , and 3-ferrocenyl-2,4,5-tri(β-naphthyl)cyclopentadienone, 27 , have also been prepared and their Diels-Alder reactivity exploited [ 46 , 47 ]. As shown in Figure 13 , tetra(β-naphthyl)cyclopentadienone and di(β-naphthyl)acetylene, 28 , undergo [4 + 2] cycloaddition and, after decarbonylation, yield hexa(β-naphthyl)benzene, 29 .…”

“…In hexa(β-naphthyl)benzene the six peripheral substituents are oriented in a propeller fashion with dihedral angles of 60° [ 46 ]. However, there is a disorder because the molecule exists as a mixture of eight conformers whereby the naphthyls can be aligned all syn, i.e., 6:0, or in a 5:1 arrangement, or 4:2 (1,2), (1,3) or (1,4), or 3:3 (1,2,3), (1,2,4) or (1,3,5).…”