Homogeneous Ziegler-Natta catalysis: Synthetic, kinetic, and thermodynamic studies examining olefin polymerization catalyst formation and behavior.

摘要

The following dissertation examines the synthesis and energetics of L ₂MR+ B(C₆F₅)₂Ar − systems in relation to their importance as active catalysts for olefin polymerization. Generally, formation of the complexes involves as in: L₂M(Me)R + B(C₆F₅)₂Ar → L₂MR+ B(C₆F₅)₂Ar −. Abstraction enthalpies are measured in toluene solution by titration calorimetry and variable-temperature 1H NMR. Dynamic reorganization that symmetrizes the ion-pair is also investigated by variable-temperature 1H NMR experiments over a wide solvent and temperature range.; The metals investigated are predominantly M = Zr and Hf, although some examples of M = Ti are included. Zirconium complexes are generally more synthetically accessible, have more favorable formation energies, looser ion-pairing, and greater olefin polymerization activities than comparable Hf complexes. Stabilization of the metal cation and promotion of loose ion-pairing is best obtained with ancillary ligations and substituents most capable of offering electron density and steric protection to the metal center. For instance, ligation such as L₂ = (Me₅Cp)₂ is more stabilizing than L ₂ = Cp₂, and R = CH(TMS)₂ is more stabilizing than R = Me. Formation of cation-anion pair structures is also investigated as a function of the strength of the B(C₆F₅)₂Ar Lewis acid and the solvent dielectric constant. Increasing the electron withdrawing ability of the Ar group from Ar = C₆H₅ to C₆F _{as do increases in solvent dielectric constant.}