Synthesis and characterization of a pyrazolium bearing N-heterocyclic carbene–palladium(II) complex

3,5-Dichloro-1,2-diphenylpyrazolium tetrafluoroborate 1 reacts at 0 °C with 2,6-dimethylphenol in the presence of triethylamine to give the 5-chloro-3-aryloxy-1,2-diphenylpyrazolium tetrafluoroborate 2 (58% yield). Heterocycle 2 reacts with 1-methylimidazole affording 5-(1-methyl-1H-imidazolium-3-yl)-3-aryloxy-1,2-diphenylpyrazolium chloride tetrafluoroborate 3 in 83% yield. When half an equivalent of allylchloropalladium dimer [Pd(allyl)Cl]2 is added to 3 in the presence of triethylamine, monocationic compound 4 featuring an N-heterocyclic carbene coordinated to allylchloropalladium(II) is isolated in 72% yield. All compounds have been fully characterized by multinuclear NMR spectroscopy. We also describe the X-ray crystal structure of 4, which crystallizes in the monoclinic C2/c space group.

Graphical abstractPyrazolium bearing N-heterocyclic carbene palladium(II) complex.Figure optionsDownload full-size imageDownload as PowerPoint slide