Highly Efficient Carborane-Based Activators for Molecular Olefin Polymerization Catalysts

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.