468726-18-3Relevant articles and documents
Weakly coordinating Al-, Nb-, Ta-, Y-, and La-based perfluoroaryloxymetalate anions as cocatalyst components for single-site olefin polymerization
Metz, Matthew V.,Sun, Yimin,Stern, Charlotte L.,Marks, Tobin J.
, p. 3691 - 3702 (2008/10/08)
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 Y3- 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.
