Thermodynamics of metallocene catalyst activation: alignment of theory and experiment

Abstract

Three equilibria involved in metallocene catalyst activation, including dissociation of R₆Al₂ (R = Me, Et or i-Bu) and related species such as [L₂ZrMe₂AlMe₂][B(C₆F₅)₄] (L₂ = Cp₂, 1,2-ethylenebis(η⁵-indenyl), Me₂C(η⁵-C₅H₄)₂) or [(L₂ZrMe)₂μ-Me][MePBB] (L₂ = (h⁵-1,2-Me₂C₅H₃)₂, [MePBB]⁻ = [MeB(Ar_F)₃]⁻ with Ar_F = o-C₆F₅-C₆F₄) are studied by DFT using various approaches to account for the enthalpy and entropy changes in gas and condensed phases. These studies reveal that both low energy vibrations and translational entropy conspire to cause significant deviations between theory and experiment when it comes to the free energy change in condensed or even gas phase. Alignment of theory with experiment requires in addition, consideration of specific solvation of reactants and products.