We report the synthesis, isolation, and characterization of a stable donor–acceptor substituted ortho-quinodimethane (oQDM). This system with an imidazolidine scaffold as the donor can also be referred to as acceptor-substituted ortho-N-heterocyclic quinodimethane (oNHQ). We have examined the extent of polarization of the conjugated π-system using single-crystal X-ray diffraction, NMR and UV/vis spectroscopy, cyclic voltammetry, and DFT computations. The bond lengths in the phenyl linker do not exhibit the alternation typical of oQDMs. In addition, the ¹³C and ¹⁵N NMR shifts suggest significant charge separation, an interpretation supported by the diatropic ring current determined by NICS_ZZ(r) computations, which is characteristic of aromatic compounds. DFT calculations show that polarization is an electronic effect that is amplified by steric influences. More strikingly, the oxidation and reduction potentials of the push–pull substituted oQDM are virtually identical to those of authenticated anionic and cationic derivatives. The results therefore indicate that an aromatic zwitterionic structure represents the electronic structure more accurately than a neutral quinoidal Lewis structure, which indicates that the acceptor-substituted oNHQ is a rare example of an organic zwitterion in which the centers of charge are in conjugation. The ambiphilic reactivity of the acceptor-substituted oNHQ, which is evidenced by the dehydrogenation of ammonia borane and the addition of phenylacetylene via heterolytic C–H bond cleavage, further supports its notation as an organic zwitterion and is reminiscent of frustrated Lewis pairs (FLPs). Thus, the acceptor-substituted oNHQ can be considered to be an intramolecular carbogenic FLP in terms of its reactivity.

中文翻译：

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受体取代的 N-杂环邻喹二甲烷：突破供体-受体取代多烯的极化界限


我们报道了稳定供体-受体替代的邻喹二甲烷 （oQDM） 的合成、分离和表征。这种以咪唑烷支架为供体的系统也可以称为受体取代的邻位 N-杂环喹二甲烷 （oNHQ）。我们使用单晶 X 射线衍射、NMR 和 UV/vis 光谱、循环伏安法和 DFT 计算检查了共轭 π 系统的极化程度。苯基接头中的键长不表现出 oQDM 的典型交替。此外，¹³C 和 ¹⁵N NMR 偏移表明显着的电荷分离，NICS_ZZ（r） 计算确定的变异性环电流支持了这一解释，这是芳香族化合物的特征。DFT 计算表明，极化是一种被空间影响放大的电子效应。更引人注目的是，推挽取代的 oQDM 的氧化和还原电位与鉴定的阴离子和阳离子衍生物的氧化和还原电位几乎相同。因此，结果表明，芳香族两性离子结构比中性喹状 Lewis 结构更准确地代表了电子结构，这表明受体取代的 oNHQ 是电荷中心共轭的有机两性离子的罕见例子。 受体取代的 oNHQ 的模相似性反应性，这可以通过氨硼烷的脱氢和通过异质溶解 C-H 键裂解添加苯乙炔来证明，进一步支持其作为有机两性子的符号，并让人想起沮丧的路易斯对 （FLP）。因此，就其反应性而言，受体取代的 oNHQ 可以被认为是分子内产碳 FLP。