Synthesis and structural characterization of metal complexes based on pyrazole/imidazolium chlorides

A series of imidzoalium salt, L · HCl, for the potentially bidentate pyrazole/N-heterocyclic carbene was synthesized. Reactions of a 2:1 mixture between L · HCl bearing bulky N-substitution and Ag₂O produced Ag(L)Cl, whereas a novel compound with unique stoichiometry AgL₂(AgCl)_0.5Cl was produced from L · HCl bearing N-methyl group under identical condition. Reactions of L · HCl with PdCl₂ produced zwitterionic Pd^IICl₃L · H. Selected structural determinations on L · HCl, Ag(L)Cl, AgL₂(AgCl)_0.5Cl, and Pd^IICl₃L · H revealed intriguing crystal chemistry in which the less-stable gauche rotamers were obtained exclusively. A preliminary application of the zwitterionic complexes, Pd^IICl₃L · H, in Heck coupling reaction of aryl bromide with n-butyl acrylate shows effective activity.