Yakimov Alexander V, Kaul Christoph J, Kakiuchi Yuya, Sabisch Sebastian, Bolner Felipe Morais, Raynaud Jean, Monteil Vincent, Berruyer Pierrick, Copéret Christophe
Department of Chemistry and Applied Biosciences, Laboratory of Inorganic Chemistry, Surface & Interfacial Chemistry, Eidgenössische Technische Hochschule Zürich, HCI, Vladimir-Prelog-Weg 2, CH-8093 Zurich, Switzerland.
PolyCatMat Team, UMR 5128 - CP2M (Catalysis, PolymerizationProcesses & Materials), Université de Lyon, CNRS, Université Lyon 1, CPE Lyon, 69616 Villeurbanne, France.
J Phys Chem Lett. 2024 Mar 21;15(11):3178-3184. doi: 10.1021/acs.jpclett.3c03119. Epub 2024 Mar 13.
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.
用BCl处理齐格勒-纳塔（ZN）催化剂可通过增加活性位点的数量来提高其活性。在此，我们展示了钛固态核磁共振（NMR）光谱如何使我们能够在使用烷基铝活化之前，了解此类经处理的ZN预催化剂中存在的钛表面位点的电子结构。通过对预催化剂和相应分子类似物进行密度泛函理论（DFT）建模增强的高场（21.1 T）和低温（约100 K）NMR，能够检测钛NMR信号，并在分子水平上理解钛表面位点的电子结构。相关的钛表面位点呈现出钛NMR信号（δ = -170 ppm； = 9.3 MHz；κ = 0.05），对应于吸附在MgCl载体扭曲表面上的明确的全氯化六配位钛位点，这是在用BCl进行后处理并去除烷氧基配体后形成的，与聚合活性的提高相一致。
