The catalytic system of iron(III) compound/alkylaluminum/1,10-phenothroline() has been long disclosed for efficient 3,4-selective polymerization of isoprene to achieve semi-crystalline 3,4-polyisoprene product, that finds important application in the current tire industry. Nevertheless, such a system is highly sensitive to the steric nature of ligands, even a subtle variation (. introducing methyl group to its 2,9-position) will result in significantly decreased catalytic activities. In this research, we disclose a facile method, in-situ addition of borate salts, that can well address such a long unsolved issue. By doing such, the pristine catalytic activities were able to be greatly enhanced ( 4-fold higher) without damaging the selectivity of the active species. Such a method was also applicable for various substituted ligands, such as , ., which greatly broadens the ligand scope of such iron(III) based catalytic system. Mechanistic studies revealed that the attraction of alkyl group by borate salts to form the cationic active species might play a governing role in enhancing the activities.

中文翻译：

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铁基体系异戊二烯的3,4-选择性聚合：硼酸盐在增强催化活性和拓宽1,10-菲咯啉配体范围方面的关键作用

铁(III)化合物/烷基铝/1,10-酚咯啉()的催化体系早已被公开用于异戊二烯的有效3,4-选择性聚合以获得半结晶3,4-聚异戊二烯产物，该体系在以下领域具有重要应用：当前的轮胎行业。然而，这样的系统对配体的空间性质高度敏感，即使是细微的变化（在其2,9位引入甲基）也会导致催化活性显着降低。在这项研究中，我们公开了一种简便的方法，即原位添加硼酸盐，可以很好地解决这样一个长期未解决的问题。通过这样做，原始催化活性能够大大增强（高出 4 倍），而不会损害活性物质的选择性。这种方法也适用于各种取代的配体，例如，，，这大大拓宽了这种铁（III）基催化体系的配体范围。机理研究表明，硼酸盐吸引烷基形成阳离子活性物质可能在增强活性方面发挥主导作用。