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

摘要

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 16 pi antiaromatic system. A single-crystal X-ray diffraction analysis of MDAP(0) revealed a distorted quinoidal structure with high bond-length alternation. The H-1 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 16 pi-electron conjugation.