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Unexpected Precatalyst σ‑Ligand Effects in Phenoxyimine Zr‑Catalyzed Ethylene/1-Octene Copolymerizations

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journal contribution
posted on 24.04.2019, 00:00 by Yanshan Gao, Matthew D. Christianson, Yang Wang, Jiazhen Chen, Steve Marshall, Jerzy Klosin, Tracy L. Lohr, Tobin J. Marks
Recent decades have witnessed intense research efforts aimed at developing new homogeneous olefin polymerization catalysts, with a primary focus on metal-Cl or metal-hydrocarbyl precursors. Curiously, metal-NR2 precursors have received far less attention. In this contribution, the Zr-amido complex FI2ZrX2 (FI = 2,4-di-tert-butyl-6-((isobutyl­imino)­methyl)­phenolate, X = NMe2) is found to exhibit high ethylene polymerization activity and relatively high 1-octene coenchainment selectivity (up to 7.2 mol%) after sequential activation with trimethyl­aluminum, then Ph3C+B­(C6F5)4. In sharp contrast, catalysts with traditional hydrocarbyl ligands such as benzyl and methyl give low 1-octene incorporation (0-1.0 mol%). This unexpected selectivity persists under scaled/industrial operating conditions and was previously inaccessible with traditional metal-Cl or -hydrocarbyl precursors. NMR, X-ray diffraction, and catalytic control experiments indicate that in this case an FI ligand is abstracted from FI2Zr­(NMe2)2 by trimethylaluminum in the activation process to yield a catalytically active cationic mono-FIZr species. Heretofore this process was believed to serve only as a major catalyst deactivation pathway to be avoided. This work demonstrates the importance of investigating diverse precatalyst monodentate σ-ligands in developing new catalyst systems, especially for group 4 olefin polymerization catalysts.

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