Mohammed Muqtar, Nele Marcio, Al-Humydi Abdulaziz, Xin Shixuan, Stapleton Russell A, Collins Scott
Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1.
J Am Chem Soc. 2003 Jul 2;125(26):7930-41. doi: 10.1021/ja0207706.
Propylene polymerization using unsymmetrical, ansa-metallocene complexes Me(2)Y(Ind)CpMMe(2) (Y = Si, C, M = Zr, Y = C, M = Hf) and the co-initiators methyl aluminoxane (PMAO), B(C(6)F(5))(3), and [Ph(3)C][B(C(6)F(5))(4)] was studied at a variety of propylene concentrations. Modeling of the polymer microstructure reveals that the catalysts derived from Me(2)Si(Ind)CpZrMe(2) 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 [C(3)H(6)] in the case of catalysts derived from Me(2)C(Ind)CpHfMe(2) and PMAO, or [Ph(3)C][B(C(6)F(5))(4)], but the average tacticity of the polymer produced at a given [C(3)H(6)] decreased in the order [Ph(3)C][B(C(6)F(5))(4)] > PMAO. With B(C(6)F(5))(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 (Delta) but otherwise feature essentially invariant, intrinsic stereoselectivity for monomer insertion (alpha, beta), 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 C(s)-symmetric Me(2)C(Flu)CpZrMe(2) complex with different counterions. For every counterion investigated, the principle difference appears to be the operating regime (Delta) rather than intrinsic differences in insertion stereoselectivity (alpha). Surprisingly, the ordering of the various counterions with respect to Delta does not agree with commonly accepted ideas about their coordinating ability. In particular, catalysts when activated with B(C(6)F(5))(3) appear to function at low values of Delta as compared to those featuring B(C(6)F(5))(4) (less coordinating) and FAl(o-C(6)F(5))C(6)F(4) (more coordinating) or PMAO (more coordinating) counterions where the ordering in Delta is MeB(C(6)F(5))(3) < B(C(6)F(5))(4) < FAl(o-C(6)F(5))C(6)F(4) approximately PMAO. Possible reasons for this behavior are discussed.
研究了使用不对称桥联茂金属配合物Me(2)Y(Ind)CpMMe(2)（Y = Si、C，M = Zr；Y = C，M = Hf）以及助引发剂甲基铝氧烷（PMAO）、B(C(6)F(5))(3)和[Ph(3)C][B(C(6)F(5))(4)]在多种丙烯浓度下进行的丙烯聚合反应。聚合物微观结构的建模表明，由Me(2)Si(Ind)CpZrMe(2)与这些助引发剂中的每一种衍生的催化剂在链反转比链增长快得多的条件下（柯廷-哈梅特条件）起作用。令人惊讶的是，所形成的聚丙烯的微观结构基本上不受抗衡离子性质的影响，这表明双态催化剂固有基本参数的值相似。对于由Me(2)C(Ind)CpHfMe(2)和PMAO或[Ph(3)C][B(C(6)F(5))(4)]衍生的催化剂，聚丙烯的立构规整度对[C(3)H(6)]的变化敏感，但在给定[C(3)H(6)]下制备的聚合物的平均立构规整度按[Ph(3)C][B(C(6)F(5))(4)] > PMAO的顺序降低。使用B(C(6)F(5))(3)时，形成的聚合物更具立构规整性，其微观结构对单体浓度的变化不变。在这种情况下，聚丙烯的五元组分布可以通过假设所有三种催化剂/助催化剂组合以不同的插入与反转相对速率（Δ）起作用来建模，但除此之外，单体插入的固有立构选择性（α，β）基本不变，而存在的异构离子对的相对反应性/稳定性（g/K）似乎仅受到适度影响（如果有影响的话）。关于具有不同抗衡离子的C(s)对称Me(2)C(Flu)CpZrMe(2)配合物已发表的丙烯聚合行为也可得出类似结论。对于所研究的每种抗衡离子，主要差异似乎在于操作区域（Δ），而不是插入立构选择性（α）的固有差异。令人惊讶的是，各种抗衡离子相对于Δ的排序与关于它们配位能力的普遍接受观点不一致。特别是，与以B(C(6)F(5))(4)（配位能力较弱）和FAl(o-C(6)F(5))C(6)F(4)（配位能力较强）或PMAO（配位能力较强）为抗衡离子的情况相比，用B(C(6)F(5))(3)活化的催化剂似乎在较低的Δ值下起作用，其中Δ的排序为MeB(C(6)F(5))(3) < B(C(6)F(5))(4) < FAl[(o-C(6)F(5))C(
