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

• Published in: Journal of the American Chemical Society 2019-05, Vol.141 (19), p.7822-7830
• Main Authors: Gao, Yanshan, Christianson, Matthew D, Wang, Yang, Chen, Jiazhen, Marshall, Steve, Klosin, Jerzy, Lohr, Tracy L, Marks, Tobin J
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.9b01445

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.