On Conformational Flexibility of Half-Titanocene Catalysts with Aryloxy Ligands for High-Temperature Olefin Polymerization Processes: Static and Dynamic Theoretical Studies

Abstract

The static DFT calculations and Car-Parrinello molecular dynamic simulations were performed for a series of half-metallocene ethylene-polymerization catalysts based on Ti(I V) complexes with aryloxy ligands, varied in cyclopentadienide Cp/Cp* and 2,6-di-/2-monosubstituted phenoxy ligand combinations. The results confirm the more pronounced conformational flexibility of the monosubstituted systems, demonstrated by a relatively easy rotation of the aryloxy ligand. In the case of the complex with a 2-phenylphenoxy ligand, a substantial decrease in rotational barrier is observed due to the secondary interactions between the phenyl substituent and the methyl protons of Cp*. In the catalytically active species derived from the corresponding precatalysts, the barrier for the ligand rotation is decreased compared to the precatalysts. For the monosubstituted aryloxy complexes such an easy rotation allows for the transition between the "nonreactive" and "reactive" propagation pathways (anti and son), which can lead to an increase in their catalytic activity.