Well-Defined N-Heterocyclic Carbene-Palladium Complexes as Efficient Catalysts for Domino Sonogashira Coupling/Cyclization Reaction and C-H bond Arylation of Benzothiazole

摘要

Well-defined and air-stable PEPPSI (Pyridine Enhanced Precatalyst Preparation Stabilization and Initiation) themed palladium bis-N-heterocyclic carbene complexes have been developed for the domino Sonogashira coupling/cyclization reaction of 2-iodophenol with a variety of terminal alkynes and C-H bond arylation of benzothiazole with aryl iodides. The PEPPSI themed palladium complexes, 2a and 2b were synthesized in good yields from the reaction of corresponding imidazolium salts with PdCl2 and K2CO3 in pyridine. The new air-stable palladium-NHC complexes were characterized by NMR spectroscopy, X-ray crystallography, elemental analysis, and mass spectroscopy studies. The PEPPSI themed palladium(II) bis-N-heterocyclic carbene complexes 2a and 2b exhibited excellent catalytic activities for domino Sonogashira coupling/cyclization reaction of 2-iodophenol with terminal alkynes yielding benzofuran derivatives. In addition, the palladium complexes, 2a and 2b successfully catalyzed the direct C-H bond arylation of benzothiazole with aryl iodides as coupling partners in presence of CuI as co-catalyst.