A Density Functional Theory Study on the Ligand Substitution Mechanism of a Square Planar Pd Complex

摘要

The mechanisms of ligand substitution reactions of PdCl2(CH3CN)(2) with PPh3 and P(OPh)(3) ligands were investigated by computational calculations using density functional theory (DFT). Contrary to the conventional associative mechanism of a 16-electron Pd complex, substitutions of two acetonitrile ligands in PdCl2(CH3CN)(2) with PPh3 or P(OPh)(3) adopt dissociative pathways. The first PdCl2(CH3CN)(2)+PPh3 -> PdCl2(CH3CN)(PPh3)+CH3CN step takes I-d mechanism and the following PdCl2(CH3CN)(PPh3) -> PdCl2(PPh3)(2)+CH3CN step does D mechanism. The overall free energy barriers (G(max)(double dagger)) of two separate steps were 26.4 and 20.4kcal/mol, respectively. Similar reaction with P(OPh)(3) ligands takes D mechanism for both first and second substitutions with G(max)(double dagger) values of 30.3 and 21.0kcal/mol, respectively.