π-烯丙基稀土配合物的合成、结构及其催化烯烃聚合反应机理的研究——Ⅱ.LiY(π-C_3H_5)_4·2.5D催化异戊二烯聚合反应机理的研究

SYNTHESES AND CHARACTERIZATION OF THE π-ALLYL- RARE EARTH COMPLEXES AND STUDIES ,ON THE MECHENISM OF OLIFEN POLYMERIZATIONII.SIUDIES ON MECHENISM OF ISOPRE NE POLYMERIZATION IN THE PRESENOE OF [LI(2.5D)] [Y(π-G_3H_5)_4]

在稀土配位共轭双烯烃聚合反应机理的研究中,一般认为按π-烯丙基机理进行,但迄今为止尚缺乏足够的实验证据。我们曾用~1H-NMR、一维^(13)C-NMR和二维^(13)C-NMR系统地研究了(CF_3COO)_2LnCl·EtoH-(i-Bu)_2AIH-共轭双烯烃(Ln=La、Pr、Nd、Sm、Tb、Ho、Sc和Y)均相聚合体系的聚合机理,提出了η~4-共轭双烯(顺式-反式-)和η~3-烯丙基(同式-对式-)机理。但由于广烯丙基稀土配合物稳定性差,难于合成,加之聚合体系中很难直接分离出π-烯丙基稀土配合物活性体,为此,至今尚未能用模型π-烯丙基稀土配合物对上述机理进行研究。

[Li(2.5D)] [Y(π-C3H5)4] was used as a catalyst for isoprene polymerization giving 57.9% cis-1,4 polyisoprene with high activity. The result of 13C-NMR study on the polymer shows that the terminal chains are -CH2-CH = CH1 which indicates that the insertion reaction of monomer occured between belween yttrium and π-allyl. The result above is the first direct evidence for the π-alyl mechenism of diene polymerization with rare earth coordination catalysts.