Alternating oligo(op-phenylenes) via ruthenium catalyzed diol–diene benzannulation: orthogonality to cross-coupling enables de novo nanographene and PAH construction

摘要

Ruthenium(0) catalyzed diol–diene benzannulation is applied to the conversion of oligo(p-phenylene vinylenes) >2a–c, >5 and >6 to alternating oligo(o,p-phenylenes) >10a–c, >11–13. Orthogonality with respect to conventional palladium catalyzed biaryl cross-coupling permits construction of p-bromo-terminated alternating oligo(o,p-phenylenes) >10b, >11–13, which can be engaged in Suzuki cross-coupling and Scholl oxidation. In this way, structurally homogeneous nanographenes >16a–f are prepared. Nanographene >16a, which incorporates 14 fused benzene rings, was characterized by single crystal X-ray diffraction. In a similar fashion, p-bromo-terminated oligo(p-phenylene ethane diol) >9, which contains a 1,3,5-trisubstituted benzene core, is converted to the soluble, structurally homogeneous hexa-peri-hexabenzocoronene >18. A benzothiophene-terminated pentamer >10c was prepared and subjected to Scholl oxidation to furnish the helical bis(benzothiophene)-fused picene derivative >14. The steady-state absorption and emission properties of nanographenes >14, >16a,>b,>d,>e,>h and >18 were characterized. These studies illustrate how orthogonality of ruthenium(0) catalyzed diol–diene benzannulation with respect to classical biaryl cross-coupling streamlines oligophenylene and nanographene construction.