Cationic Pyridylamido Adsorbate on Bronsted Acidic Sulfated Zirconia: A Molecular Supported Organohafnium Catalyst for Olefin Homo- and Co-Polymerization

摘要

Here we report the combined application of high resolution solid-state C-13-CPMAS-NMR and FT-IR spectroscopy, elemental analysis, kinetic poisoning/active site counting, variable dielectric constant medium, and DFT computation to characterize the surface chemistry of a pyridylarnido hafnium complex (Cat1, L-1-HfMe2, L-1 = 2,6-diisopropyl-N-{(2-isopropylphenyl))[6-(naphthalen-1-yl)pyridin-2-yl]methyl}aniline) adsorbed on Bronsted acidic sulfated zirconia (ZrS). The spectroscopic and DFT results indicate protonolytic formation of organohafnium cations having a largely electrostatic pyridylamido-Hf-CH3+ ... ZrS- interaction with elongated Hf ... OZES distances of, similar to 2.14 A. High-molecular-weight polyethylenes and ethylene/1-octene copolymers are obtained with this supported catalyst without an activator/cocatalyst. The DFT calculations reveal that the first ethylene insertion into the Hf-methyl bond has a lower barrier than the corresponding insertion into the Hf-aryl bond of this single-site heterogeneous catalyst.