Thiophene‐Fused 1,4‐Diazapentalene: A Stable C=N‐Containing π‐Conjugated System with Restored Antiaromaticity

Abstract

A thiophene-fused 1,4-diazapentalene (TAP) was rationally designed and synthesized as a C=N-containing 4n π-electron system that exhibits restored antiaromaticity impaired by the doping with C=N bonds. X-ray crystallographic analysis and quantum chemical calculations revealed that the annulation of thiophene rings with the 1,4diazapentalene moiety resulted in a much higher antiaromaticity than the pristine 1,4-diazapentalene. These effects can be ascribed to the reduced bond alternation of the eightmembered-ring periphery caused by stabilization of the less-stable bond-shifted resonance structure upon increasing the degree of substitution of imine moieties. Consequently, TAP underwent facile hydrogenation even under mild conditions because of its pronounced antiaromaticity and the high aromaticity of the corresponding hydrogenated product H 2 -TAP. In addition, the electrophilic C=N moieties in TAP led to the formation of a dense π-stacked structure. These results highlight the effect of partial replacement of C=C bonds with C=N bonds in antiaromatic π-electron systems.

Aromaticity controls the excited-state properties of host–guest complexes of nanohoops

“…Replacing nitrogen atoms with carbons causes an increase in HOMO energy. 29 It should be noted that a wavefunction node, where the wavefunction is zero and changes signs, was found on a single C-C bond connecting DHPP units in the tetramer (Fig. S3, ESI †).…”

“…28 Doping antiaromatic hydrocarbons with nitrogen leads to an increase in their electron-withdrawing ability. 29,30 In this work, we report a theoretical study of aromaticity, electronic and photoinduced electron transfer (PET) properties of the complexes based on C 60 fullerene with nanohoops built from benzene-fused antiaromatic pyrrolo [3,2-b]pyrrole (PP) and its aromatic analog 1,4-dihydropyrrolo [3,2-b]pyrrole (DHPP). The structural units have already been synthesized and characterized, 31,32 whereas the nanohoops were modeled based on the similarity to [4]CDBP .…”

7,12‐Dihydrobenzo[de]indolo[3,2‐b]quinoline: Unique Reactivity and Redox Interconversion

“…Finally, we investigated the redox interconversion of 9 , which possesses two oxidizable NH groups (Figure 4). The screening of various oxidizing agents revealed that NiO 2 [5f,16] provided the optimum results in terms of reaction efficiency and reproducibility. After the treatment of 9 with NiO 2 , chromatographic purification provided the corresponding oxidized form 11 in 86 % yield.…”

Manifestations of Antiaromaticity in Organic Materials: Case Studies of Cyclobutadiene, Borole, and Pentalene

“…[95] formed 105, which rapidly dimerized only to 106 b (2) deprotonation and CuCl 2 mediated oxidative coupling affording both 106 a and 106 b. Subsequent photolysis of the dimers in a frozen argon matrix afforded the free parent pentalene (105). IR data suggests that pentalene has highly localized single and double bonds, a characteristic of antiaromatic species.…”

“…NICS values confirmed that the pentalene centers between the phenanthrene fused molecules were more antiaromatic than dibenzopentalene; furthermore, the computational data suggested that there was a linear correlation between the localized aromaticities within the phenanthrene fusions and the antiaromaticity of the pentalene core. While there has been work on tuning the antiaromaticty by “doping” the pentalene core directly via the installation of nitrogen atoms within the pentalene core, [105] Oshima's work suggests a rational way of tuning the antiaromaticity of the native pentalene core by judicious use of ring fusion.…”