Weakly coordinating Al-, Nb-, Ta-, Y-, and La-based perfluoroaryloxymetalate anions as cocatalyst components for single-site olefin polymerization

Reaction of LiAlH₄, with 4.0 equiv of HOC₆F₅ in toluene leads to H₂ evolution and formation of Li⁺Al(OC₆F₅)₄^-; subsequent metathesis with Ph₃CCl then yields the corresponding trityl tetrakis(pentafluorophenoxo)aluminate, Ph₃C⁺Al(OC₆F₅)₄^- (4). The pentachlorides MCl₅ (M = Nb, Ta) undergo reaction with 6.0 equiv of LiOC₆F₅ in Et₂O to afford crystalline Li(OEt₂)_n⁺-{[M(OC₆F₅) ₄(μ₂-OC₆F₅)₂]₂ Li}·C₇H₈ salts (M = Nb, n = 4 (5a); M = Ta, n = 3 (5b)), which can be cleanly converted with Ph₃CCl to the corresponding mononuclear, thermally stable Ph₃C⁺M(OC₆F₅)₆^- salts (M = Nb (6a); M = Ta (6b)) in high yield. 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 C₆F₅O^- 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 (C₅Me₅)₂ZrMe₂ in THF-d₈. In situ activation of (C₅Me₅)₂ZrMe₂ and (C₅Me₄H)₂ZrMe₂ with 4 and 6 yields efficient ethylene polymerization catalysts, having activities comparable to those of Ph₃C⁺B(C₆F₅)₄^- -activated systems under identical polymerization conditions. To impede aryloxide ring transfer, a bulkier ligand, 2-nonafluorobiphenoxide (C₁₂F₉O^-), was combined with highly oxophilic Y^3- and La³⁺ centers. Reaction of M[CH(SiMe₃)₂]₃ (M = Y, La) with 4.0 equiv of 2-HOC₁₂F₉ results in the clean formation of M(OC₁₂F₉)₃(HOC₁₂F₉) complexes (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)₂ZrMe₂ yield highly active ethylene polymerization systems.