Weakly Coordinating Al-, Nb-, Ta-, Y-, and La-Based Perfluoroaryloxymetalate Anions as Cocatalyst Components for Single-Site Olefin Polymerization

Reaction of LiAlH 4 with 4.0 equiv of HOC 6 F 5 in toluene leads to H 2 evolution and formation of Li + Al(OC 6 F 5 ) 4 -; subsequent metathesis with Ph 3 CCl then yields the corresponding trityl tetrakis(pentafluorophenoxo)aluminate, Ph 3 C + Al(OC 6 F 5 ) 4 - ( 4 ). The pentachlorides MCl 5 (M = Nb, Ta) undergo reaction with 6.0 equiv of LiOC 6 F 5 in Et 2 O to afford crystalline Li(OEt 2 ) n + {[M(OC 6 F 5 ) 4 (μ 2 -OC 6 F 5 ) 2 ] 2 Li}·C 7 H 8 salts (M = Nb, n = 4 ( 5a ); M = Ta, n = 3 ( 5b )), which can be cleanly converted with Ph 3 CCl to the corresponding mononuclear, thermally stable Ph 3 C + M(OC 6 F 5 ) 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−C 6 F 5 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 C 6 F 5 O - transfer from Nb/Ta to Zr/Ti is observed. However, (C 5 Me 5 ) 2 ZrMe(THF- d 8 ) + Nb(OC 6 F 5 ) 6 - ( 7 ) is formed in the reaction of 6a with (C 5 Me 5 ) 2 ZrMe 2 in THF- d 8 . In situ activation of (C 5 Me 5 ) 2 ZrMe 2 and (C 5 Me 4 H) 2 ZrMe 2 with 4 and 6 yields efficient ethylene polymerization catalysts, having activities comparable to those of Ph 3 C + B(C 6 F 5 ) 4 - -activated systems under identical polymerization conditions. To impede aryloxide ring transfer, a bulkier ligand, 2-nonafluorobiphenoxide (C 12 F 9 O - ), was combined with highly oxophilic Y 3+ and La 3+ centers. Reaction of M[CH(SiMe 3 ) 2 ] 3 (M = Y, La) with 4.0 equiv of 2-HOC 12 F 9 results in the clean formation of M(OC 12 F 9 ) 3 (HOC 12 F 9 ) complexes (M = Y ( 9a ); M = La, ( 9b )) in high yield. When 9 is paired with metallocene dimethyl precursors, even sterically open precatalysts such as CGCTiMe 2 (CGC = Me 2 Si(C 5 Me 4 ) t BuN) or (C 5 H 5 ) 2 ZrMe 2 yield highly active ethylene polymerization systems.