Thiophene-fused 1,4-Diazapentalene: A Stable C=N-Containing π-Conjugated System with Restored Antiaromaticity
Thiophene-fused 1,4-Diazapentalene: A Stable C=N-Containing π-Conjugated System with Restored Antiaromaticity
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噻吩稠合 1,4-二氮杂戊二烯：具有恢复反芳香性的稳定 C=N π 共轭体系
DOI：
10.1002/chem.202103122
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
A. Fukazawa
中科院分区：
文献类型：
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作者：
J. Usuba;A. Fukazawa
合理设计并合成了一种噻吩-融合1,4 -重氮戊二烯（TAP），作为含C=N -的4n π -电子体系，其抗芳香性被C=N键的掺杂所破坏。X射线晶体学分析和量子化学计算表明，与原始的1,4 -重氮戊二烯相比，噻吩环上的1,4 -重氮戊二烯环的抗芳性要高得多。这些效应可以归因于随着亚胺基取代度的增加，较不稳定的键移共振结构变得稳定，从而减少了八元环外围的键交替。因此，由于其明显的抗芳香性和相应的氢化产物H2‐TAP的高芳香性，即使在温和的条件下，TAP也容易加氢。此外，TAP中的亲电性C=N基团导致形成致密的π‐堆叠结构。这些结果强调了反芳香π电子体系中C=C键被C=N键部分取代的影响。
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 1,4‐diazapentalene 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 eight‐membered‐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 H2‐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.