Pyrazole-3-carboxylates assisted N-heterocyclic carbene palladium complexes: synthesis, characterization, and catalytic activities towards arylation of azoles with arylsulfonyl hydrazides

Four mononuclear and dinuclear pyrazole-3-carboxylates assisted NHC-Pd complexes have been synthesized and characterized. Notably, the bridge-cleavage reactions of [Pd(mu-Cl)(Cl)(NHC)](2) with 1H-pyrazole-3-carboxylic acid afforded dinuclear complexes [(NHC)Pd(mu-1H-pyrazolato-3-carboxylate)](2), in which the 1H-pyrazolato-3-carboxylate was employed as a N<^>N<^>O dianionic chelating and bridging ligand. To further explore the structural features and catalytic properties of the complexes, 1-methyl-1H-pyrazole-3-carboxylic acid was introduced into the coordination with [Pd(mu-Cl)(Cl)(NHC)](2) and the corresponding mononuclear complexes (NHC)PdCl(1-methyl-1H-pyrazole-3-carboxylate) were obtained. The catalytic properties of the complexes in desulfitative arylation of azoles with arylsulfonyl hydrazides were initially investigated.