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Synthesis of NBN-Type Zigzag-Edged Polycyclic Aromatic Hydrocarbons: 1,9-Diaza-9a-boraphenalene as a Structural Motif

A novel class of dibenzo-fused 1,9-diaza-9a-boraphenalenes featuring zigzag edges with a nitrogen boron nitrogen bonding pattern named NBN-dibenzophenalenes (NBN-DBPs) has been synthesized: Alternating nitrogen and boron atoms impart high chemical stability to these zigzag-edged polycyclic aromatic hydrocarbons (PAHs), and this motif even allows for postsynthetic modifications, as demonstrated here through electrophilie bromination and subsequent palladium-catalyzed cross-coupling reactions. Upon oxidation, as a typical example, NBN-DBP 5a was nearly quantitatively converted to sigma-dimer 5a,-2 through an open-shell intermediate, as indicated by UV-vis-NIR absorption spectroscopy and electron paramagnetic resonance spectroscopy corroborated by spectroscopic calculations, as Well as 2D NMR spectra analyses. In situ spectroelectrochemistiy was used to confirm the formation process of the dimer radical cation 5a-2(center dot+). Finally, the developed new synthetic strategy could also be applied to obtain pi-extended NBN-clibentoheptazethrene (NBN-DBHZ), representing an efficient pathway toward NBN-doped zigzag-edged graphene nanoribbons.

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