Highly Efficient Carborane-Based Activators for Molecular Olefin Polymerization Catalysts
Sebastian Günther, Qingheng Lai, Todd D. Senecal, Rafael Huacuja, Sean Bremer, David Pearson, Jessica C. DeMott, Nattamai Bhuvanesh, Oleg V. Ozerov, Jerzy Klosin
Abstract
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.