Synthesis, structure, and hydrolytic reaction of trans-dichlorobis(diethanolamine-N)palladium(II) with N-acetylated L-histidylglycine dipeptide

The reaction of PdCl2, or K2PdCl4, with diethanolamine (DEA), in the molar ratio 1:2, affords the trans-[PdCl2(DEA)2] complex. X-ray structure analysis of this complex confirmed the formation of the trans-isomer. The complex crystallizes in the space group P42bc. The central Pd(II) ion is coordinated in an almost ideal square-planar fashion with a small deformation of the Cl–Pd–Cl angle (175.6(7)°) due to N–H⋯Cl hydrogen bonding. The N–H group participates in a bifurcated interaction with the two symmetry related Cl− anions. The hydroxyl groups of the diethanolamine ligand form very strong hydrogen bonds between the complex units, thus leading to infinite zigzag (O–H⋯O–H⋯O–H ··) chains in the crystal packing. The complex units are further connected by weaker intermolecular hydrogen bonds of the N–H⋯Cl type in a way to form layers parallel to the crystallographic (001) plane. The reaction between the trans-[PdCl2(DEA)2] or trans-[Pd(H2O)2(DEA)2]2+ complex and MeCOHis-Gly dipeptide at 1.5 < pH < 2.0 and at 25 °C leads to the regioselective cleavage of the amide bond involving the carboxylic group of the histidine. The cleavage of the substrate was fast and went almost to completion within less than one hour.