Isolation and characterisation of a stable 2-azaphenalenyl azomethine ylide

Abstract

Although azomethine ylides have been fully exploited as versatile reactive intermediates in dipolar cycloaddition reactions to construct a variety of heterocyclic compounds involving a nitrogen atom, little is known about their structural and electronic properties. Here a method is developed for the preparation, isolation and characterization of a stable 2-azaphenalenyl based azomethine ylide. N-Phenyl-5,8-di-t-butyl-2-azaphenalenyl cannot be isolated because it undergoes rapid dimerization by CC bond formation at the 1 and 3 positions. In contrast, sterically bulkier N-2,6-di(isopropyl)phenyl-5,8-di-t-butyl-2-azaphenalenyl can be generated and isolated as deep green crystals under deoxygenated conditions. X-ray crystal analysis of this stable azomethine ylide reveals that its azaphenalenyl skeleton has very small bond alternation and structural deformation. The results of spectroscopic and electrochemical theoretical studies indicate that N-2,6-di(isopropyl)phenyl-5,8-di-t-butyl-2-azaphenalenyl has electronic features that are similar to those of phenalenyl anion and it possesses an extremely high HOMO energy.

2‐Aryl‐1H‐benz[de]isoquinolinium Ions: Cationic Dyes Displaying Mechanochromism and Crystallochromism

“…On the other hand, the λ ABS of 1 b (433 nm (log ϵ =3.86) is only slightly shorter than that of 1 a . The result suggests that π‐conjugation between the 2,6‐di(isopropyl)‐substituted phenyl group and the 1 H ‐benz[ de ]isoquinolinium moiety in 1 b is almost completely retarded by a sterically governed increase in the torsion angle [5] . Notably, 1 b exhibits intense fluorescence with maxima (λ FL‐SL and λ FL‐SD ) in CH 2 Cl 2 and in the solid state that are greatly blue‐shifted and emission quantum yields that are larger [λ FL‐SL =529 nm, Φ SL =0.60, and λ FL‐SD =527 nm, Φ SD =0.25) compared to those of 1 a (λ FL‐SL =555 nm, Φ SL =0.11, and λ FL‐SD =609 nm, Φ SD =0.03).…”

“…By utilizing the procedure described previously, [5,10] 1,8dibromomethyl-3,6-di-tert-butylnaphthalene (6), a building block for preparation of the 2-aryl-5,8-di-tert-butyl-1Hbenz[de]isoquinolines 7 a-e, was prepared from 3,6-di-tertbutylnaphthalene 1,8-dicarboxylic anhydride (5). Subsequent amination reactions of 6 with the corresponding anilines in the presence of triethylamine (Et 3 N) in toluene produced the respective 1H-benz[de]isoquinolines 7 a-e (Scheme 2).…”

“…The result suggests that π-conjugation between the 2,6-di(isopropyl)-substituted phenyl group and the 1Hbenz[de]isoquinolinium moiety in 1 b is almost completely retarded by a sterically governed increase in the torsion angle. [5] Notably, 1 b exhibits intense fluorescence with maxima (λ FL-SL and λ FL-SD ) in CH 2 Cl 2 and in the solid state that are greatly blueshifted and emission quantum yields that are larger [λ FL-SL = Table 1. Absorption and fluorescence spectral data of 1 a-e, 4 a and 4 b in CH 2 Cl 2 and in the solid state.…”

“…DFT calculations for 1 a-e were carried out by using the B3LYP/6-31G(d,p) method with the Gaussian 09 program package. [14] 1,8-Dibromomethyl-3,6-di-tert-butylnaphthalene (6), [5,12] 1,8-dibromo-methylnaphthalene, [11] 2-phenyl-2,3-dihydro-1Hbenz[de]isoquinoline, [11] 2-[2,6-di(isopropyl)phenyl]-3,6-di-tert-butyl-2,3-dihydro-1H-benz[de]iso-quinoline (7 b), [5] 2-phenyl-2,3-dihydro-1H-benz[de]isoquinolinium tetrafluoroborate (4 a), [11] [5] were prepared using reported procedures.…”

“…Iminium ion containing dyes, like cyanine dyes, are of particular interest because of their use in a variety of fluorescent sensor, [1] biological imaging, [2] optoelectronic device [3] and other applications [4] . In a recent study, we synthesized N ‐[2,6‐di(isopropyl)phenyl]‐5,8‐di‐ tert ‐butyl‐2‐azaphenalenyl ( 2 b ), the first isolable azomethine ylide derivative (Scheme 1), [5] and the unstable analog 2 a , [6] via deprotonation reactions of the corresponding 2‐aryl‐5,8‐di‐ tert ‐butyl‐1 H ‐benz[ de ]isoquinolinium tetrafluoroborates 1 a and 1 b . At that time, we observed that the iminium salts 1 a – b exhibit intense fluorescence both in solution and in the solid state.…”