Palladium complexes (palladium acetate and palladium chloride) and phosphine ligand binding reactions are commonly involved in homogeneous Pd catalytic reactions as part of Pd(0)/Pd(II) redox cycle. Additionally, phosphine ligands are commonly used in the synthesis of colloidal Pd nanoparticles to control the nucleation or growth kinetics. The thermodynamics of binding between the ligands and Pd can provide insights on modifying and optimizing the reactivity of Pd. However, when comparing different metal-ligand binding strengths, most experimental and theoretical studies are only focused on the enthalpic contribution to the binding equilibrium, whereas the binding entropy and stoichiometry can be critical factors.<br/>Isothermal titration calorimetry (ITC) is a highly sensitive technique capable of measuring the isotherm of the metal complex – ligand binding to obtain the thermodynamic properties (Gibbs free energy, enthalpy, entropy and binding stoichiometry). We will present a new ITC method making use of the low-content (≤ 10 %) of Pd acetate monomers to measure the low-K (equilibrium constant) of Pd acetate trimer dissociation which is beyond ITC measuring limit, as well as the thermodynamics of ligand-monomer binding and monomer content (purity). Furthermore, we will present a systematic experimental and theoretical study combining ITC with density functional theory (DFT) calculations on the enthalpic and entropic effects of different phosphine ligands binding to Pd complexes (palladium acetate and palladium chloride). The effect of chain length on binding strength, especially the less studied entropic contribution, and its effect on kinetics of colloidal Pd nanoparticle synthesis will be discussed.

Thermodynamics of ligand-metal complex binding: An isothermal titration calorimetry study

255th National Meeting (2018)

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