New perfluoroarylborane activators for single-site olefin polymerization. Acidity and cocatalytic properties of a "superacidic" perfluorodiboraanthracene

The synthesis, Lewis acid properties, and single-site olefin polymerization characteristics of catalyst systems utilizing the binuclear organo-Lewis acid cocatalyst 9, 10-bis(pentafluorophenyl)-9, 10-diboraoctafluoroanthracene, C₁₂F₈B₂(C₆F₅)₂ (8b), are reported. X-ray diffraction analysis of 8b reveals a nearly planar C₁₂F₈B₂ core with -C₆F₅ rings rotated 75° out of the plane, hindering π communication between the pendant -C₆F₅ substituents and the C₁₂F₈B₂ core, and thereby enhancing Lewis acidity at the boron centers. Competition equilibration experiments with 8b, B(C₆F₅)₃, and acetonitrile over a wide temperature range demonstrate that 8b is a stronger Lewis acid than B(C₆F₅)₃ by ΔH = +1.4(2) kcal/mol and ΔS = -5.3(1) eu. The diffraction-derived molecular structure of 8b←NCCH₃ reveals substantial skeletal reorganization only at the coordinated boron center. When it is paired with dimethyl organo-group 4 catalyst precursors, 8b affords extremely efficient single-site olefin polymerization systems in both laboratory and large-scale reactors. In all cases, 8b forms polymerization systems with higher activities than those utilizing B(C₆F₅)₃ as the cocatalyst.