Kinetics, mechanism and DFT calculations on base hydrolysis of -amino acid esters catalyzed by [Pd(TMPDA)(H2O)2]2+

Abstract

Pd(TMPDA)Cl2 (TMPDA = N,N,N`,N`-tetramethyl-1,3-propanediamine) was synthesized and characterized by elemental analysis. [Pd(TMPDA)(H2O)2]2+ reacts with amino acid esters (L) to form mixed ligand [Pd(TMPDA)L]2+ complexes. The kinetics of base hydrolysis of [Pd(TMPDA)L]2+ was studied by pH-stat technique and the corresponding rate constants are reported. The coordinated glycine methyl ester is efficiently hydrolyzed, whereas the coordinated methionine methyl ester is hydrolysed with a much lower catalytic activity. The catalytic influence is depended on the mode of coordination of the ester to the palladium complex. Probable mechanisms for these reactions are considered. Activation parameters for the hydrolysis of the coordinated glycine methyl ester were determined experimentally. DFT calculations (B3LYP/LANL2DZ) were applied to determine the possible mechanism of the base hydrolysis of the amino acid esters. The calculations are discussed in reference to the reported experimental data.