Direct C—H Bond Activation of Benzoxazole and Benzothiazole with Aryl Bromides Catalyzed by Palladium(II)‐N‐heterocyclic Carbene Complexes

• Published in: Chinese journal of chemistry 2018-09, Vol.36 (9), p.837-844
• Main Authors: Kaloğlu, Murat, Kaloğlur, Nazan, Özdemir, İsmail
• Format: Article
• Language: English
• Subjects: Activation; Aromatic compounds; benzimidazolium bromide; benzoazoles; Benzothiazole; Bromides; Catalysis; Catalysts; direct C—H bond activation; Hydrogen bonds; Infrared spectroscopy; NMR; Nuclear magnetic resonance; N‐heterocyclic carbene; Palladium; Reagents
• ISSN: 1001-604X; 1614-7065
• DOI: 10.1002/cjoc.201800166

Herein, we report that a series of novel palladium(II)‐NHC complexes (NHC=N‐heterocyclic carbene) were synthesized. The structures of all novel complexes were characterized by 1H NMR, 13C NMR, FT‐IR spectroscopy and elemental analysis techniques. These palladium(II)‐NHC complexes were tested as efficient catalysts in the direct C—H bond activation of benzoxazole and benzothiazole with aryl bromides in the presence of 1 mol% catalyst loading at 150 °C for 4 h. Under the given conditions, various aryl bromides were successfully applied as the arylating reagents to achieve the 2‐arylbenzoxazoles and 2‐arylbenzothiazoles in acceptable to high yields. Six new palladium(II)‐NHC complexes with the general molecular formula [PdBr2(NHC)2], (NHC=1,3‐dialkylbenzimidazol‐2‐ylidene) were synthesized. The obtained complexes were fully characterized by analytical and spectral methods such as elemental analysis, FT‐IR, 1H NMR and 13C NMR. The catalytic activity of all the palladium(II)‐NHC complexes have been evaluated in the C—H bond activation of benzoxazole and benzothiazole with aryl bromides in moderate to high yields.