Pd(II)-Pd(II) bonding interaction in dinuclear Pd(II) complex with non-macrocyclic (O&N) chelates: characterization, kinetics and DFT study

Abstract

A unique PdII complex with metal-metal(d8-d8) bonding interaction, [Pd(pic)(cbdca)]2∙H2O 4 (where, pic = 2-aminomethylpyridine and cbdca2- = cyclobutane-1,1-dicarboxylate) has been synthesised and characterized by X-ray structure, FT-IR, ESI Mass, Raman and NMR spectroscopy. Density Functional Theory (DFT) study shows PdII-PdII bond distance of 3.18 Å in complex 4 which is close to the observed distance of 3.1790(1) Å found from X-ray crystal structure. Powder X-ray structure of [Pd(pic)Cl2] 1 has been solved and polymeric chain structure is found without any supporting ligand. At pH 5.5, complex [Pd(pic)(OH2)2](ClO4)2 2, the hydrolyzed product of 1 exists as dimeric complex [Pd(pic)(OH)]2(ClO4)2 3. Third order kinetics is followed for the reaction of cbdca with the di-μ-hydroxo bridged dimer 3. The substitution process is a ligand-dependent second order reaction, found to take place in two consecutive steps in accordance with the rate law kobs = k1[cbdca]2. The reaction follows an associative mechanistic path and the activation parameters (ΔH# and ΔS#) for both the steps were evaluated using Eyring equation.