Sterically Encumbered (Perfluoroaryl) Borane and Aluminate Cocatalysts for Tuning Cation-Anion Ion Pair Structure and Reactivity in Metallocene Polymerization Processes. A Synthetic, Structural, and P
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- 作者：You-Xian (Eugene) Chen ; Matthew V. Metz ; Liting Li ; Charlotte L. Stern ; and Tobin J. Marks
- 刊名：Journal of the American Chemical Society
- 出版年：1998
- 出版时间：July 1, 1998
- 年：1998
- 卷：120
- 期：25
- 页码：6287 - 6305
- 全文大小：696K
- 年卷期：v.120,no.25(July 1, 1998)
- ISSN：1520-5126
文摘
The synthesis and dialkyl abstraction chemistry aswell as the unusual cocatalytic characteristics inmetallocene-mediated polymerization of two distinctive borane andaluminate cocatalysts tris(2,2',2''-nonafluorobiphenyl)borane (PBB) and triphenyl carbeniumtris(2,2',2''-nonafluorobiphenyl)fluoroaluminate,(Ph3C+PBA-) are reported.Reaction of PBB with Cp'2ThMe2 (Cp'= 
5-C5Me5),CGCZrMe2 (CGC = Me2Si(5-Me4C5)(tBuN)),and Cp'MMe3 (M = Zr, Hf) cleanly affords base-freecationic complexesCp'2ThMe+MePBB-(1), CGCZrMe+MePBB-(5), andCp'MMe2+MePBB- (M = Zr,7; Hf, 8). In case ofCGCTiMe2 and dimethyl zirconocenes, 
-methyl dinuclearcationic complexes[(CGCTiMe)2(-Me)]+MePBB-(6) and[(L2ZrMe)2(-Me)]+MePBB-(L = 5-C5H5 (Cp),2;5-1,2-Me2C5H3(Cp''), 3; Cp', 4; L2 =Me2Si(Ind)2, Ind =5-C9H6, 9;L2 = Me2C(Flu)(Cp), Flu =5-C13H8, 10) areformed. A similar reaction withPh3C+PBA- results in thecorresponding complexesCGCZrCH3+PBA- (M = Zr,19; Ti, 20) andL2ZrCH3+PBA-(L = Cp, 15b; Cp'', 16;5-1,3-(SiMe2)2C5H3,17; Cp', 18; L2 =Me2Si(Ind)2, 21;L2 = Me2C(Flu)(Cp), 22). Two dinuclear complexes3 and 13([Me2C(Flu)(Cp)Zr(C6F5)]2(-F)+MeB(C6F5)3-)derivedfrom borane PBB and B(C6F5)3,respectively, and three other PBA--based monomericcomplexes 14(Ph3C+PBA-),19, and 21 have been characterized by X-raydiffraction, and these determinations allow detailedanalysis of the ion pairing in the solid state. In combinationwith solution dynamic NMR, all data indicateMePBB--cation interactions to be considerably weakerthan those involvingMeB(C6F5)3-,while the stronglyion-paired chiral PBA- converts previously enantiomericcations into pairs of diastereomers. As revealed bydynamic 1H NMR studies, ion pairreorganization/symmetrization in 5 is significantly morerapid than in theMeB(C6F5)3-analogue, suggesting much looser ion pairing in 5. Onthe other hand, PBA- racemization isa rapid process (e.g., 
G
(58 
C) =16.9(2) kcal/mol for 16), whilecation-PBA- ion pairs have higherbarriers for ion pair symmetrization than in analogous fluoroarylborates. Dinuclear complexes 2 and 3initiateefficient polymerization of methyl methacrylate (MMA) to producesyndiotactic poly(methyl methacrylate)(PMMA), while 9 produces highly isotactic PMMA, andsterically more accessible complexes 6 and 10exhibitno activity. For olefin polymerization and copolymerization,PBB-derived cationic complexes, both monomericand dinuclear, generally exhibit higher catalytic activity andcomonomer incorporation levels than theMeB(C6F5)3-analogues, with CGC catalysts exhibiting the greatest activitycontrasts. On the other hand,PBA--derived complexes exhibit a remarkable sensitivityof olefin polymerization characteristics and ion pairingto ancillary ligand bulk, with activity differences of up to106-fold observed. In regard tostereospecificpolymerization, PBA--derived chiral complex 21produces highly isotactic polypropylene whileB(C6F5)4--derived analogue produces isotactic polypropylene with lowerisotacticity under similar conditions. Microstructure analyses of poly(ethylene-co-1-hexene) samplesindicate that PBB enhances comonomer incorporationrandomness.
5-C5Me5),CGCZrMe2 (CGC = Me2Si(5-Me4C5)(tBuN)),and Cp'MMe3 (M = Zr, Hf) cleanly affords base-freecationic complexesCp'2ThMe+MePBB-(1), CGCZrMe+MePBB-(5), andCp'MMe2+MePBB- (M = Zr,7; Hf, 8). In case ofCGCTiMe2 and dimethyl zirconocenes, -methyl dinuclearcationic complexes[(CGCTiMe)2(-Me)]+MePBB-(6) and[(L2ZrMe)2(-Me)]+MePBB-(L = 5-C5H5 (Cp),2;5-1,2-Me2C5H3(Cp''), 3; Cp', 4; L2 =Me2Si(Ind)2, Ind =5-C9H6, 9;L2 = Me2C(Flu)(Cp), Flu =5-C13H8, 10) areformed. A similar reaction withPh3C+PBA- results in thecorresponding complexesCGCZrCH3+PBA- (M = Zr,19; Ti, 20) andL2ZrCH3+PBA-(L = Cp, 15b; Cp'', 16;5-1,3-(SiMe2)2C5H3,17; Cp', 18; L2 =Me2Si(Ind)2, 21;L2 = Me2C(Flu)(Cp), 22). Two dinuclear complexes3 and 13([Me2C(Flu)(Cp)Zr(C6F5)]2(-F)+MeB(C6F5)3-)derivedfrom borane PBB and B(C6F5)3,respectively, and three other PBA--based monomericcomplexes 14(Ph3C+PBA-),19, and 21 have been characterized by X-raydiffraction, and these determinations allow detailedanalysis of the ion pairing in the solid state. In combinationwith solution dynamic NMR, all data indicateMePBB--cation interactions to be considerably weakerthan those involvingMeB(C6F5)3-,while the stronglyion-paired chiral PBA- converts previously enantiomericcations into pairs of diastereomers. As revealed bydynamic 1H NMR studies, ion pairreorganization/symmetrization in 5 is significantly morerapid than in theMeB(C6F5)3-analogue, suggesting much looser ion pairing in 5. Onthe other hand, PBA- racemization isa rapid process (e.g., G(58 C) =16.9(2) kcal/mol for 16), whilecation-PBA- ion pairs have higherbarriers for ion pair symmetrization than in analogous fluoroarylborates. Dinuclear complexes 2 and 3initiateefficient polymerization of methyl methacrylate (MMA) to producesyndiotactic poly(methyl methacrylate)(PMMA), while 9 produces highly isotactic PMMA, andsterically more accessible complexes 6 and 10exhibitno activity. For olefin polymerization and copolymerization,PBB-derived cationic complexes, both monomericand dinuclear, generally exhibit higher catalytic activity andcomonomer incorporation levels than theMeB(C6F5)3-analogues, with CGC catalysts exhibiting the greatest activitycontrasts. On the other hand,PBA--derived complexes exhibit a remarkable sensitivityof olefin polymerization characteristics and ion pairingto ancillary ligand bulk, with activity differences of up to106-fold observed. In regard tostereospecificpolymerization, PBA--derived chiral complex 21produces highly isotactic polypropylene whileB(C6F5)4--derived analogue produces isotactic polypropylene with lowerisotacticity under similar conditions. Microstructure analyses of poly(ethylene-co-1-hexene) samplesindicate that PBB enhances comonomer incorporationrandomness.