Schulich Faculty of Chemistry, Institute of Catalysis Science and Technology, Technion-Israel Institute of Technology, Technion City, 32000 Haifa, Israel.
J Am Chem Soc. 2012 Oct 17;134(41):17234-44. doi: 10.1021/ja3071545. Epub 2012 Oct 3.
The use of bis(1,3-di-tert-butylimidazolin-2-iminato) titanium dichloride (1) and dimethyl (2) complexes in the polymerization of propylene is presented. The complexes were activated using different amounts of methylalumoxane (MAO), giving in each case a very active catalytic mixture and producing polymers with a narrow molecular weight distribution (polydispersity = 1.10). The use of the cocatalyst triphenylcarbenium (trityl) tetra(pentafluorophenyl)borate totally inhibits the reaction, producing the corresponding bis(1,3-di-tert-butylimidazolin-2-iminato) titanium(III) methyl complex, the trityl radical ((•)CPh(3)), the anionic MeB(C(6)F(5))(4)(-), B(C(6)F(5))(3), and the bis(1,3-di-tert-butylimidazolin-2-iminato) titanium(IV) dimethyl·B(C(6)F(5))(3) complex. The use of a combination of physical methods such as NMR, ESR-C(60), and MALDI-TOF analyses enabled us to propose a plausible mechanism for the polymerization of propylene, presenting that the polymerization is mainly carried out in a living fashion. In addition, we present a slow equilibrium toward a small amount of a dormant species responsible for 2,1-misinsertions and chain transfer processes.
本文介绍了双（1,3-二-叔丁基咪唑啉-2-亚基）二氯化钛（1）和二甲基（2）配合物在丙烯聚合中的应用。使用不同量的甲基铝氧烷（MAO）对配合物进行活化，在每种情况下都得到了非常活性的催化混合物，并产生了具有较窄分子量分布（多分散性=1.10）的聚合物。使用助催化剂三苯基碳鎓（三苯甲基）四（五氟苯基）硼酸盐会完全抑制反应，生成相应的双（1,3-二-叔丁基咪唑啉-2-亚基）钛（III）甲基配合物、三苯甲基自由基（•CPh3）、阴离子 MeB（C6F5）4（-）、B（C6F5）3和双（1,3-二-叔丁基咪唑啉-2-亚基）钛（IV）二甲基·B（C6F5）3配合物。使用 NMR、ESR-C60 和 MALDI-TOF 等物理方法的组合，我们提出了丙烯聚合的合理机理，表明聚合主要以活性方式进行。此外，我们还提出了一个缓慢的平衡，其中存在少量的休眠物种，负责 2,1-插入和链转移过程。
