Sterically expanded CGC catalysts: substituent effects on ethylene and α-olefin polymerization
作者:Jianfang Chai、Khalil A. Abboud、Stephen A. Miller
DOI:10.1039/c3dt50163a
日期:——
Several analogues of the sterically expanded constrained geometry catalyst Me2Si(η1-C29H36)(η1-N-tBu)ZrCl2·OEt2 (2) were synthesized to assess the effect on branching and molecular weight for ethylene homopolymerization. Catalysts based on tetramethyltetrahydrobenzofluorene (TetH), ethylTetH, t-butylTetH, and octamethyloctahydrodibenzofluorenyl (OctH) bearing a diphenylsilyl bridge were prepared and characterized: Me2Si(η5-C21H22)(η1-N-tBu)ZrCl2 (3); Me2Si(η5-C23H26)(η1-N-tBu)ZrCl2 (4); and Me2Si(η5-C25H30)(η1-N-tBu)ZrCl2 (5); Me2Si(η5-C21H22)(η1-N-tBu)ZrMe2 (6); and Ph2Si(η5-C29H36)(η1-N-tBu)ZrCl2 (7). Complexes 4, 5, 6, and 7 were characterized by X-ray crystallography and displayed η5 hapticity to the carbon ring in each case, in contrast to 2. In comparison to 2, complexes 3, 4, 5, and 7 (in combination with methylaluminoxane = MAO) showed diminished branching, higher molecular weight, and higher polydispersity indices for obtained ethylene homopolymers. While 4/MAO produced the greatest molecular weight polymers, no branching was observed. Reactivity ratios were determined for the copolymerization of ethylene and 1-decene with 2/MAO. A value of rethylene = 14.9 and an exceedingly high value of r1-decene = 0.49 were foundâin line with previous reports of this catalyst's unusual affinity for α-olefins.
为了评估支化和分子量对乙烯均聚反应的影响,合成了立体扩张限制几何催化剂Me2Si(η1-C29H36)(η1-N-tBu)ZrCl2·OEt2 (2)的几种类似物。制备并表征了基于四甲基四氢二苯并芴(TetH)、乙基TetH、叔丁基TetH和八甲基八氢二苯并芴基(OctH)承载二苯硅桥的催化剂:Me2Si(η5-C21H22)(η1-N-tBu)ZrCl2 (3);Me2Si(η5-C23H26)(η1-N-tBu)ZrCl2 (4);以及Me2Si(η5-C25H30)(η1-N-tBu)ZrCl2 (5);Me2Si(η5-C21H22)(η1-N-tBu)ZrMe2 (6);和Ph2Si(η5-C29H36)(η1-N-tBu)ZrCl2 (7)。通过X射线晶体学对4、5、6和7进行表征,与2不同,这些配合物在每个碳环上都显示出η5的配位度。与2相比,配合物3、4、5和7(与甲基铝氧烷=MAO组合)得到的乙烯均聚物的支化程度降低,分子量更高,多分散性指数更高。尽管4/MAO生成了最高分子量的聚合物,但没有观察到分支。测定了乙烯和1-癸烯共聚反应中2/MAO的反应性比率。得到了rethylene = 14.9和极高的r1-癸烯 = 0.49的值,这与之前报道的该催化剂对α-烯烃的异常亲和力一致。