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

Abstract

Here we report the combined application of high-resolution solid-state 13C–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 pyridylamido hafnium complex (Cat1, L1-HfMe2, L1 = 2,6-diisopropyl-N-{(2-isopropylphenyl)­[6-(naphthalen-1-yl)­pyridin-2-yl]­methyl}­aniline) adsorbed on Brønsted 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···OZrS distances of ∼2.14 Å. 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.

Preparation of Pyridylamido Hafnium Complexes for Coordinative Chain Transfer Polymerization

“…In other catalysis [performed with Pd complexes constructed via N-heterocyclic carbene (NHC) ligands], the influence of substituents at the 2,6-position in aryl-N moieties is substantial, and derivatization of the NHC ligand has been carried out by replacing common 2,6-diisopropylphenyl-N parts with 2,6-di(3-pentyl)phenyl-N and 2,6-di(3-heptyl)phenyl-N moieties [30,31]. Much research has also been performed on I [32][33][34][35][36][37][38], and the synthesis of its analogs with the aim to improve the catalytic performance deserves attention [7,29,[39][40][41][42]. Subtle change in the ligand framework sometimes results in dramatic improvement in the polymerization performance and, hence, modification of the substituents has been a main research theme in the development of postmetallocecenes [43][44][45][46][47][48][49].…”

Preparation of Pincer Hafnium Complexes for Olefin Polymerization

“…By performing anionic polymerization of styrene in a one-pot reaction after CCTP with I , it is also possible to synthesize polyolefin-polystyrene block copolymers [23,24,25]. In this context, many studies have been performed to detail I and to improve the catalytic performance by modifying the skeleton of I [26,27,28,29,30,31,32,33,34,35]. With an aim to develop upgraded catalyst for I , we prepared various pincer-type Hf-complexes.…”

Beyond the Active Site. Cp*ZrMe3/Sulfated Alumina‐Catalyzed Olefin Polymerization Tacticity via Catalyst⋅⋅⋅Surface Ion‐Pairing

“…We recently reported that organo‐Hf precatalyst chemisorption on sulfated ZrO 2 or Al 2 O 3 (ZrS or AlS) yields ethylene homo‐ and 1‐hexene copolymerization catalysts with ∼80 % catalytically significant Hf centers [9a] . Surprisingly, similar activity and copolymerization selectivity trends prevail in the homogeneous analogues.…”