New Perfluoroarylborane Activators for Single-Site Olefin Polymerization. Acidity and Cocatalytic Properties of a “Superacidic” Perfluorodiboraanthracene
作者:Matthew V. Metz、David J. Schwartz、Charlotte L. Stern、Tobin J. Marks、Peter N. Nickias
DOI:10.1021/om020079b
日期:2002.9.1
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 75degrees out of the plane, hindering pi 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 DeltaH = +1.4(2) kcal/mol and DeltaS = -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.