- Kinetic and mechanism of alkene polymerization
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Triphenylmethyl salts of the very weakly-coordinating borate anions [CN{B(C6F5)3}2]- (1), [H2N{(C6F5)3}2] - and [M{CNB(C6F5)3} 4]2- (M = Ni, Pd) have been prepared in simple one-pot reactions. Mixtures of (SBI)ZrMe2/1/AlBu 3 i (SBI = rac-Me2Si(Ind)2) are 30-40 times more active in ethylene polymerizations at 60-100°C than (SBI)ZrCl2/MAO. The quantification of anion effects on propene polymerization activity at 20°C gives the order [CN{B(C6F5)3}2] - > [H2N{(C6F5)3} 2]- ≈ B(C6F5) 4 - ? [MeB(C6F5)3]-. The highest productivities were of the order of ca. 3.0 × 108 g PP (mol Zr)-1 h-1 [C3H6]-1, about 1.3-1.5 times higher than with B(C6F5) 4 - as the counter anion. The titanium system CGCTiMe 2/1/AlBu 3 i gave activities that were very similar to the zirconocene catalyst. The concentration of active species [C*] as determined by quenched-flow kinetic techniques indicates typical values of around 10%, independent of the counter anion, for both the borate and MAO systems. Pulsed field-gradient spin echo and nuclear Overhauser effect NMR experiments on systems designed to be more realistic models for active species with longer polymeryl chains, (SBI)M(CH2SiMe3)(μ-Me) B(C6F5)3 and [(SBI)MCH2SiMe 3 + ...B(C6F5) 4 - ] (M = Zr, Hf), demonstrated the influence of bulky alkyl chains on the ion pair solution structures: while the MeB(C6F 5)3 compound exists as a simple inner-sphere ion-pair, the B(C6F5) 4 - compound is an outer-sphere ion pair (OSIP), a consequence of the relegation of the anion into the second coordination sphere by the γ-agostic interaction with the alkyl ligand. The OSIP aggregates to ion hextuples (10 mM) or quadruples (2 mM). Implications for the polymerization mechanism are discussed; the process follows an associative interchange (I a) pathway. MAIK Nauka/Interperiodica , 2006.
- Bochmann,Cannon,Song
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- Synthesis, structures, and reactivity of weakly coordinating anions with delocalized borate structure: The assessment of anion effects in metallocene polymerization catalysts
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The formation of adducts of tris(pentafluorophenyl)borane with strongly coordinating anions such as CN- and [M(CN)4]2- (M = Ni, Pd) is a synthetically facile route to the bulky, very weakly coordinating anions [CN{B(C
- Zhou,Lancaster,Walker,Beck,Thornton-Pett,Bochmann
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p. 223 - 237
(2007/10/03)
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- New weakly coordinating counter anions for high activity polymerisation catalysts: [(C6F5)3B-CN-B(C6F5)3]- and [Ni{CNB(C6F5)3}4}2-
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The new borate [CPh3]+[CN{B(C6F5)3}2]- and the anionic isocyanoborate complex [Ni{CNB(C6F5)3}4]2- are readily accessible in one-pot reactions and act as a highly efficient activators for metallocene polymerisation catalysts; turnover numbers of up to 53,000 s-1 appear to be the highest reported so far for ethene polymerisation catalysts.
- Lancaster, Simon J.,Walker, Dennis A.,Thornton-Pett, Mark,Bochmann, Manfred
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p. 1533 - 1534
(2007/10/03)
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