We describe the two-electron reduction of N,N′-dimethyl-2,7-diazapyrenium dications (MDAP²⁺), which afforded the corresponding reduced form (MDAP⁰) as a highly electron-rich 16π antiaromatic system. A single-crystal X-ray diffraction analysis of MDAP⁰ revealed a distorted quinoidal structure with high bond-length alternation. The ¹H NMR spectrum of MDAP⁰ exhibited a diagnostic proton signal (4.6 ppm) that is distinctly upfield shifted compared to that of aromatic diazapyrene (8.3 ppm). Theoretical calculations supported the existence of a paratropic ring current. These results indicate that MDAP⁰ exhibits antiaromatic character derived from its peripheral 16π-electron conjugation.

中文翻译：

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16π 抗芳族 2,7-二氢二氮杂芘的合成与表征：嵌有氮的抗芳族多环烃

我们描述了 N,N'-二甲基-2,7-二氮杂芘 dics ( MDAP ²⁺ ) 的双电子还原，它提供了相应的还原形式 ( MDAP ⁰ ) 作为高度富电子的 16π 抗芳香系统。MDAP ⁰的单晶 X 射线衍射分析揭示了具有高键长交替的扭曲醌式结构。MDAP ⁰的¹ H NMR 光谱显示出诊断质子信号 (4.6 ppm)，与芳族二氮杂芘 (8.3 ppm) 相比，该信号明显向上场位移。理论计算支持副热带环流的存在。这些结果表明MDAP ⁰ 表现出源自其外围 16π-电子共轭的抗芳香特性。