New cocatalysts for Ziegler-Natta olefin polymerization.

摘要

The synthesis, Lewis acid characteristics, and Ziegler-Natta single-site olefin polymerization behavior of catalyst systems utilizing the binuclear Lewis acid octafluoro-9,10-bis-pentafluorophenyl-9,10-dihydro-9,10-diboraanthracene, C₁₂F₈B₂(C₆F₅)2 ( 8b), are reported. X-ray diffraction analysis of 8b reveals a nearly planar C₁₂F₈B₂ core with −C ₆F₅ rings rotated 75° out of the plane, hindering π communication between the pendant −C₆F₅ substituents and the C₁₂F₈B₂ core, thus enhancing the Lewis acidity of the boron centers. Competition equilibration experiments of 8b and B(C₆F₅)₃ for acetonitrile measured via 19F NMR over a wide temperature range demonstrate that 8b is a stronger Lewis acid (ΔH = +1.4(2) kcal/mol and ΔS = −5.3(1) eu). When paired with dimethyl metallocene catalyst precursors, extremely efficient single-site olefin polymerization systems are formed in both laboratory and large-scale polymerization reactors.; A new class of cocatalysts for single-site olefin polymerization consisting of perfluorophenoxide ligands and devoid of group 13 elements has been synthesized, characterized, and tested for use as polymerization cocatalysts. The first set of cocatalysts utilized pentafluorophenoxide ligands: Ph₃C +Al(OC₆F₅)₄−( 4), Ph₃C+M(OC₆F₅) ₆− (M = Nb (6a); M = Ta (6b )). X-ray diffraction analysis of 6 reveals six-coordinate metal centers with substantial distortion of the M-O-C₆F₅ linkages from linearity. The reactivity and cocatalytic characteristics of 6 were investigated with respect to a series of metallocene dimethyls. For sterically unencumbered metallocenes, facile C₆F ₅O− transfer from Nb/Ta to Zr/Ti is observed. However, [(C₅Me₅)₂ZrMe(THF-d₈)] +Nb(OC₆F₅)₆− (7) is formed in the reaction of 6a with (C ₅Me₅)₂ZrMe₂ in THF-d₈. In situ activation of (C₅Me₅)₂ZrMe ₂ and (C₅Me₄H)₂ZrMe₂ with 4 and 6 yields efficient ethylene polymerization catalysts, having activities comparable to those of Ph₃C+B(C ₆F₅)₄−. To impede aryloxide ring transfer, a bulkier ligand, 2-nonafluorobiphenoxide (C₁₂F ₉O−), was combined with highly oxophilic Y +3 and La+3 centers. Reaction of M[CH(SiMe₃) ₂]₃ (M = Y, La) with 4.0 equiv. 2-HOC₁₂F ₉ results in the clean formation of H+M(OC₁₂F ₉)₄− salts (M = Y (9a); M = La, (9b)) in high yield. When 9 is paired with metallocene dimethyl precursors, even sterically open precatalysts such as CGCTiMe₂ (CGC = Me₂Si(C₅Me₄) tBuN) or (C₅H₅)₂ZrMe ₂ yield highly active ethylene polymerization systems.