Isoprene Polymerization with Iminophosphonamide Rare-Earth-Metal Alkyl Complexes: Influence of Metal Size on the Regio- and Stereoselectivity

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• 作者：Bo Liu ; Guangping Sun ; Shihui Li ; Dongtao Liu ; Dongmei Cui
• 刊名：Organometallics
• 出版年：2015
• 出版时间：August 24, 2015
• 年：2015
• 卷：34
• 期：16
• 页码：4063-4068
• 全文大小：349K
• ISSN：1520-6041

文摘

The protonolysis reaction of 尾-iminophosphonamine ligand (NPN^dipp = Ph₂P(NC₆H₃ⁱPr₂-2,6)₂) with one equivalent of rare-earth-metal tris(alkyl)s afforded the corresponding bis(alkyl) complexes NPN^dippLn(CH₂SiMe₃)₂(THF) (Ln = Sc (1), Lu (2), Y (3), Er (4)). The bis(4-methylbenzyl) complexes NPN^dippLn(CH₂Ph-4-Me)₂(THF) (Ln = Nd (5), La (6)) were prepared by treatment of the tris(4-methylbenzyl) compounds Ln(CH₂Ph-4-Me)₃(THF)₃ with 尾-iminophosphonamine ligand. The small-size rare-earth-metal-based complexes 1鈥?b>4 upon activation with AlⁱBu₃ and [Ph₃C][B(C₆F₅)₄] showed high 3,4-selectivities up to 98.1% for isoprene polymerization. When the larger size rare-earth-metal-based 4-methylbenzyl complexes 5 and 6 were employed instead, moderate 3,4-selectivities were obtained since the opening coordination environment facilitated the 1,4-enchainment (Nd³⁺: 76.1%; La³⁺: 62.9%). Replacing AlⁱBu₃ by AlEt₃, the 5 and 6 systems exhibited high activity and excellent trans-1,4 selectivity for both isoprene (96.5%, 0 掳C) and butadiene (92.8%, 20 掳C) polymerizations.