Base hydrolysis of α-amino acid esters catalysed by [Pd(N-ethylethylenediamine)(H2O)2]2+. Kinetic study and DFT calculations

Abstract

Amino acid esters (L) react with [Pd(Eten)(H2O)2]2+ (Eten=N-ethyl ethylenediamine) giving mixed ligand complexes of the type [Pd(Eten)L]2+. Base hydrolysis of [Pd(Eten)L]2+ was studied by pH-stat technique from which rate constants for the base hydrolysis of the esters were obtained. The glycine methyl ester hydrolysed significantly, whereas the methionine methyl and histidine methyl esters hydrolysed much slower. The mode of coordination of the ester plays a role in the catalysis, and possible mechanisms for these reactions are considered. Activation parameters were determined for the hydrolysis of the glycine methyl ester. The effect of the dielectric constant of the medium on the hydrolysis process was also investigated. The B3LYP/LANL2DZ method was used for geometric optimization of the free ligand and the complex using the Gaussian 09 program. The calculations are compared with the kinetic data. In addition, the vibrational frequencies of the molecules were computed for the optimized geometries.