586962-58-5

Upstream product

• 284497-56-9 ((CH₃)2C(C₉H₆)C₅H₄)Zr(CH₃)2 
• 1109-15-5 tris(pentafluorophenyl)borate 

Relevant academic research and scientific papers

Counterion effects on propylene polymerization using two-state ansa-metallocene complexes

Propylene polymerization using unsymmetrical, ansa-metallocene complexes Me2Y(Ind)CpMMe2 (Y = Si, C, M = Zr, Y = C, M = Hf) and the co-initiators methyl aluminoxane (PMAO), B(C6F5)3, and [Ph3C][B(C6F5)4] was studied at a variety of propylene concentrations. Modeling of the polymer microstructure reveals that the catalysts derived from Me2Si(Ind)CpZrMe2 and each of these co-initiators function under conditions where chain inversion is much faster than propagation (Curtin-Hammett conditions). Surprisingly, the microstructure of the PP formed was essentially unaffected by the nature of the counterion, suggesting similar values for the fundamental parameters inherent to two-state catalysts. The tacticity of PP was sensitive to changes in [C3H6] in the case of catalysts derived from Me2C(Ind)CpHfMe2 and PMAO, or [Ph3C][B(C6F5)4], but the average tacticity of the polymer produced at a given [C3H6] decreased in the order [Ph3C][B(C6F5)4] > PMAO. With B(C6F5)3, the polymer formed was more stereoregular, and its microstructure was invariant to changes in monomer concentration. The PP pentad distributions in this case could be modeled by assuming that all three catalyst/cocatalyst combinations function with different values for the relative rates of insertion to inversion (Δ) but otherwise feature essentially invariant, intrinsic stereoselectivity for monomer insertion (α, β), while the relative reactivity/stability (g/K) of the isomeric ion-pairs present seems to be only modestly affected, if at all. Similar conclusions can also be made about the published propylene polymerization behavior of the Cs-symmetric Me2C(Flu)CpZrMe2 complex with different counterions. For every counterion investigated, the principle difference appears to be the operating regime (Δ) rather than intrinsic differences in insertion stereoselectivity (α). Surprisingly, the ordering of the various counterions with respect to Δ does not agree with commonly accepted ideas about their coordinating ability. In particular, catalysts when activated with B(C6F5)3 appear to function at low values of Δ as compared to those featuring B(C6F5)4 (less coordinating) and FAl[(o-C6F5)C6F4]3 (more coordinating) or PMAO (more coordinating) counterions where the ordering in Δ is MeB(C6F5)3 6F5)4 6F5)4 6F5)C6F4]3 ≈ PMAO. Possible reasons for this behavior are discussed.

Propene polymerization using ansa-metallocenium ions: Excess activator effects on polymerization activity and polymer microstructure

The initial and steady-state rates of propene polymerization using the metallocene complexes Me2X-(Cp)IndZrMe2 (1, X = C, Si) and Me2C(Cp)FluZrMe2 (2) activated with B(C6F 5)3 increase in the presence of excess borane; the kinetic data are consistent with two different forms of the propagating catalyst in equilibrium with each other in the presence of excess borane. The ratio kplki for the ion pair [Me2C(Cp)IndZrMe][MeB(C6F 5)3] (3) is sensitive to the presence of excess borane, while the molecular structure of 3 reveals strong ion pairing in the solid state. Variable-temperature NMR spectra of (Me2C(Cp)IndZr 13Me][13 MeB(C6F5)3] in the presence of excess borane are consistent with the doubly activated intermediate Me2C(Cp)IndZr{(μ-13Me)B(C 6F5)3}2 (4) being present.