Direct C-H Bond Arylation of C2-Blocked Pyrrole with Aryl Halides Using Palladium(II)-N-Heterocyclic Carbene Catalysts

Herein we report synthesis of seven new palladium(II)-NHC complexes with the general formula [PdX2(NHC)(2)], (NHC=1,3-dialkylbenzimidazol-2-ylidene, X = Cl or Br). The structures of all the new compounds were characterized by (HNMR)-H-1, (CNMR)-C-13, FT-IR spectroscopy and elemental analysis techniques. The catalytic activities of palladium(II)-NHC complexes were tested in the direct C-H bond arylation of C2-blocked pyrrole with various aryl halides in presence of 1mol% catalyst loading at 120 degrees C for 1-16 h. Under the given conditions, palladium(II)-NHC complexes showed the good catalytic performance for the direct C-H bond arylation of C2-blocked pyrrole with aryl bromides, and with readily available and inexpensive aryl chlorides. In all cases, the C-H bond arylation regioselectively produced C5-arylated products in moderate to high yields.