Well-Defined Ti Surface Sites in Ziegler-Natta Pre-Catalysts from 47/49 Ti Solid-State Nuclear Magnetic Resonance Spectroscopy

• Published in: The journal of physical chemistry letters 2024-03, Vol.15 (11), p.3178-3184
• Main Authors: Yakimov, Alexander V, Kaul, Christoph J, Kakiuchi, Yuya, Sabisch, Sebastian, Bolner, Felipe Morais, Raynaud, Jean, Monteil, Vincent, Berruyer, Pierrick, Copéret, Christophe
• Format: Article
• Language: English
• Subjects: Catalysis; Chemical Sciences; Material chemistry; or physical chemistry; Theoretical and
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.3c03119

Treatment of Ziegler-Natta (ZN) catalysts with BCl improves their activity by increasing the number of active sites. Here we show how Ti solid-state nuclear magnetic resonance (NMR) spectroscopy enables us to understand the electronic structure of the Ti surface sites present in such treated ZN pre-catalysts, prior to activation with alkyl aluminum. High-field (21.1 T) and low-temperature (∼100 K) NMR augmented by DFT modeling on the pre-catalyst and corresponding molecular analogues enables the detection of Ti NMR signatures and a molecular level understanding of the electronic structure of Ti surface sites. The associated Ti surface sites exhibit Ti NMR signatures (δ = -170 ppm; = 9.3 MHz; κ = 0.05) corresponding to well-defined fully chlorinated hexacoordinated Ti sites adsorbed on a distorted surface of the MgCl support, formed upon post-treatment with BCl and removal of the alkoxo ligands, paralleling the increased polymerization activity.