异戊二烯稀土催化聚合过程中配合物结构及其转化的~(13)C-NMR研究

本文用~(13)C-NMR研究了异戊二烯(IP)在均相催化剂(CF_3CO_2)_2LnCl·EtOH—(i-Bu)AlH—o-C_6D_4Cl_2作用下的聚合过程。单体首先被活化同稀土配位生成η~4-IP稀土配合物(反式和顺式),然后η~4-IP的C-3和C-4插入Ln-H键生成η~3-烯丙基稀土配合物——η~3-(2-甲基)丁烯基稀土配合物(同式和对式)。二维~(13)C-NMR交换谱表明η~4-IP和0η~3-烯丙基的每对异构体在常温下分别进行慢交换反应(互变异构),这一过程使插入反应在常温下得以进行。

~(13)C-NMR STUDIES ON η~4-IP,η~3-ALLYL RARE EARTH CO MPLEXES AND THEIR TAUTOMERIZATION IN THE POLYMERIZATION PROCESSES OF ISOPRENE BASED ON (CF_3 CO_2) LnCl·EtOH-(i-Bu)_2AIH HOMOGENEOUS CATALYSTS

The polymerization processes of isoprene (IP) based on (CF3CO2)2LnCl·EtOH-(i-Bu)2AlH homogeneous catalysts were traced out by 13C-NMR. First, IP coordinated to rare earth to become η4-IP rare earth complexes (trans and cis). Then C-3 and C-4 of η4-IP inserted into Ln-H bond to form η3-allyl rare earth complexes (syn and anti). 13C chemical shifts and 1JCH coupling constants of η4-IP indicated that C-l and C-2 of η4-IP coordinated to rare earth with n coordination bond, while the double bond between C-3 and C-4 transformed to a bond to form a metal cyclopropane structure with rare earth, i.e. a activated structure.2D 13C-NMR exchange spectra showed that the slow exchange (tautomerism) reaction between every pair of η4-IP and η3-allyl isomers could take place at, ambient temperature. These reactions underwent the processes of bond breaking and reforming, which enable insert reaction to take place at room temperature. The suggestedpolymerization mechanism is IP-η4-trans-IP-η4-cis-IP--η3-syn-allyl =η3 - anti-allyl--trans-1,4-IP/cis-1,4-lP (C-1 insert) or 3,4-IP (C-3 insert) unit.