B,N-Doped Heptacenes: Ambipolar Charge-Transfer Compounds with Deep LUMO Levels.

The B,N-doped heptacene in which two ,'-dihydrophenazine units are linked by two BMes bridges (Mes = mesityl) was synthesized via fourfold Buchwald-Hartwig coupling between 2,3,6,7-tetrachloro-9,10-dimesityl-9,10-dihydro-9,10-diboraanthracene and -phenylenediamine (BuXPhos-Pd-G3, DBU/NaOTf, 2-MeTHF, 50 °C, 16 h). Upon exposure to ambient air, is oxidized to its ,'-dihydro form ; further oxidation with MnO furnishes the di(phenazine) derivative . Stirring under a blanket of H in the presence of Pd/C hydrogenates back to and ultimately . Yellow-colored is a remarkably good electron acceptor with a LUMO-energy level of -3.9 eV; upon irradiation with a 405 nm LED in the presence of THF or 1,4-cyclohexadiene, accepts two H atoms to furnish . One-electron reduction of yields the isolable radical-anion salt Li[] (lithium naphthalenide, THF, -30 °C to rt). The ambipolar compounds and possess a navy blue and deep purple color, respectively, due to charge-transfer interactions from the electron-rich ,'-dihydrophenazine donor(s) to the electron-accepting BC core.