Effect of Cp‐Ligand Methylation on Rhodium(III)‐Catalyzed Annulations of Aromatic Carboxylic Acids with Alkynes: Synthesis of Isocoumarins and PAHs for Organic Light‐Emitting Devices

• Published in: ChemPlusChem (Weinheim, Germany) Vol. 85; no. 2; pp. 334 - 345
• Main Authors: Molotkov, Alexander P., Arsenov, Mikhail A., Kapustin, Daniil A., Muratov, Dmitry V., Shepel', Nikolay E., Fedorov, Yury V., Smol'yakov, Alexander F., Knyazeva, Elena I., Lypenko, Dmitry A., Dmitriev, Artem V., Aleksandrov, Alexey E., Maltsev, Eugeny I., Loginov, Dmitry A.
• Format: Journal Article
• Language: English
• Published: Germany 01-02-2020
• Subjects: C−H activation; fluorescence; organic light-emitting diode; polycycles; rhodium catalysis; organic light-emitting diode; C−H activation; fluorescence; rhodium catalysis; polycycles
• DOI: 10.1002/cplu.202000048
• EISSN: 2192-6506

An efficient protocol was developed for the synthesis of π‐extended isocoumarins and polycyclic aromatic hydrocarbons based on the oxidative coupling of aromatic carboxylic acids with internal alkynes catalyzed by (cyclopentadienyl)rhodium complexes. The coupling chemoselectivity strongly depends on whether Cp or the methylated Cp* ligands are used. The pentamethyl derivative [Cp*RhCl2]2 predominantly gives isocoumarins, while the non‐methylated complex [CpRhI2]n produces naphthalene derivatives. The polyaromatic carboxylic acids (such as 1‐naphthoic acid, 1‐pyrenecarboxylic acid, fluorene‐1‐carboxylic acid, and dibenzofuran‐4‐carboxylic acid) are suitable for this approach. A mixture of Cp*H/RhCl3 can be used as a catalyst instead of [Cp*RhCl2]2. The structures of 3,4‐diphenylindeno[1,2‐h]isochromen‐1(11H)‐one and 7,10‐dimethyl‐8,9‐diphenylbenzo[pqr]tetraphene were determined by X‐ray diffraction. In addition, the optical properties of the prepared compounds were studied. 7,8‐Diphenyl‐10H‐phenaleno[1,9‐gh]isochromen‐10‐one was employed as an emissive layer for OLED manufacturing. The OLED emits yellow‐green light with a maximum intensity 1740 cd ⋅ m−2 at 15 V.
From catalysis to OLEDs: The selectivity of the rhodium‐catalyzed oxidative coupling of carboxylic acids and internal alkynes strongly depends on the methylation of the Cp ligand at the rhodium atom. This approach provides easy access to isocoumarins and PAHs with extended π‐conjugation for their further application as fluorescent materials. In particular, these compounds exhibit fluorescence emission in the blue‐green region (400–550 nm). Based on 7,8‐diphenyl‐10H‐phenaleno[1,9‐gh]isochromen‐10‐one as an emissive layer, the OLED structure was manufactured.