Nitrogen-doped heptazethrene and octazethrene diradicaloids.

We report the synthesis and electronic properties of nitrogen-doped heptazethrene (HZ) and octazethrene (OZ) diradicaloids, including the parent HZ-1N and OZ-1N, and the N-aryl-substituted dications, HZ-2N and OZ-2N. The unprotected HZ-1N and OZ-1N were generated in situ, but they are not stable enough for isolation. On the other hand, the N-aryl precursors 7a/7b were prepared by using a one-pot Buchwald-Hartwig amination followed by the intramolecular cyclization strategy. Chemical oxidation of 7a/7b gave the corresponding dications, HZ-2N/OZ-2N. HZ-2N displayed an open-shell singlet ground state with a moderate diradical character (y0 = 27.2%) and a small singlet-triplet energy gap (ΔES-T = -4.9 kcal mol-1). OZ-2N with larger diradical character (y0 = 54.7%) is more reactive and underwent the hydrogen abstraction reaction.