Highly Efficient Carborane-Based Activators for Molecular Olefin Polymerization Catalysts

• Published in: ACS catalysis Vol. 11; no. 6; pp. 3335 - 3342
• Main Authors: Gunther, S. Olivia, Lai, Qingheng, Senecal, Todd, Huacuja, Rafael, Bremer, Sean, Pearson, David M, DeMott, Jessica C, Bhuvanesh, Nattamai, Ozerov, Oleg V, Klosin, Jerzy
• Format: Journal Article
• Language: English
• Published: American Chemical Society 19.03.2021
• Subjects: ethylene-1-olefin copolymerization; metallocene catalysts; high-temperature solution polymerization; constrained geometry catalysts; carborane activators; ethylene polymerization
• ISSN: 2155-5435; 2155-5435
• DOI: 10.1021/acscatal.0c04228

Several ammonium carborane salts ([HNR3]­[HCB11X11], X = H, Me, Cl) were prepared and evaluated as activators with bis-metallocene and constrained geometry precatalysts at 140 and 190 °C. Activators based on undecachloro carboranes (X = Cl) led to highly active catalysts, with an overall performance very similar to the state-of-the-art borate-based activators, [HNR3]­[B­(C6F5)4], while carborane activators with X = H and Me were inactive under our polymerization conditions. Polymer samples obtained from different catalysts containing borate and carborane anions have virtually identical molecular weight and 1-octene incorporation, suggesting that these anions do not influence catalysts’ initiation, propagation, and termination kinetics. Stoichiometric reaction between constrained geometry precatalyst [(η5-C5Me4)­(SiMe2-N-t-Bu)]­TiMe2 and [Ph3C]­[HCB11Cl11] led to the formation of a complex containing a cationic μ-CH3 dimer and an unassociated carborane anion, as shown by NMR spectroscopy and single-crystal X-ray analysis. This observation is consistent with the weakly coordinating nature of halogenated carborane anions.