Pyrazolic palladium compounds containing alcohol functionality: hindered rotation around PdN bond

Reactions of the ligands 1-hydroxymethyl-3,5-dimethylpyrazole (HL1), 1-(2-hydroxyethyl)-3,5-dimethylpyrazole (HL2) and 1-(3-hydroxypropyl)-3,5-dimethylpyrazole (HL3) with [PdCl2(CH3CN)2] lead to trans-[PdCl2(HL)2] complexes. The ligands are co-ordinated to the Pd(II) by a N atom of the pyrazolic ring in a trans disposition. Two chlorides complete the environment of the metallic atom. These Pd(II) complexes were characterised by elemental analyses, conductivity measurements and IR, 1H and 13C NMR spectroscopies and X-ray diffraction. The NMR study of the complexes is consistent with a very slow rotation of ligands around the PdN bond, so that two conformational isomers can be observed in solution. The crystal structures of [PdCl2(HL)2] (HL=HL1, HL2) complexes are described. These complexes react with AgNO3 to give [Pd(NO3)(HL)2]NO3 compounds.