2,4,6-Trichlorophenyl-Substituted [3]Triangulene with Enhanced Stability

Triangulene, also known as Clar’s hydrocarbon, has been sought after by chemists for more than 70 years but with limited success. Herein, we report an oxidative dehydrogenation method to synthesize two kinetically blocked [3]triangulene derivatives TRI-1 (reported) and TRI-2 (newly synthesized), in which the three most reactive sites are substituted by bulky mesityl groups and electron-withdrawing 2,4,6-trichlorophenyl groups, and meanwhile, three vertices of triangulene are substituted by tert-butyl groups. Interestingly, the dihydro-triangulene core possesses two isomers well characterized by UV-vis, NMR spectroscopy, and X-ray crystallographic analysis, which is interestingly substituent-dependent. The newly synthesized TRI-2 is isolated in crystalline form, and X-ray crystallographic analysis reveals that the aryl substituents are nearly perpendicular to the triangulene plane and thus cause little perturbation of the electronic properties of the triangulene. Notably, 2,4,6-trichlorophenyl-substituted TRI-2 exhibits enhanced stability compared to the reported mesityl-substituted TRI-1, e.g., TRI-2 is stable for months in a crystalline state under a nitrogen atmosphere, and TRI-2 in a solution state is also more persistent than TRI-1 (half-life for TRI-1 ≈ 18 h vs. TRI-2 ≈ 132 h). This achievement will facilitate the design and synthesis of stable triangulene dimers and oligomers with higher spin multiplicity.