Synthesis and Characterization of 16π Antiaromatic 2,7‐Dihydrodiazapyrenes: Antiaromatic Polycyclic Hydrocarbons with Embedded Nitrogen

We describe the two‐electron reduction of N,N′‐dimethyl‐2,7‐diazapyrenium dications ( MDAP 2+ ), which afforded the corresponding reduced form ( MDAP 0 ) as a highly electron‐rich 16π antiaromatic system. A single‐crystal X‐ray diffraction analysis of MDAP 0 revealed a distorted quinoidal structure with high bond‐length alternation. The 1 H NMR spectrum of MDAP 0 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 MDAP 0 exhibits antiaromatic character derived from its peripheral 16π‐electron conjugation.