芳基亚胺-脒基稀土烷基化合物的合成及其催化异戊二烯聚合研究
Synthesis and Catalytic Isoprene Polymerization of Rare-Earth Alkyl Complexes Supported by An Arylimine-amidinate Ligand
Received date: 2013-04-22
Online published: 2013-05-24
Supported by
Project supported by 973 program (Grant No. 2012CB821600).
制备了芳基亚胺-脒基稀土二烷基化合物[NNN]Ln(CH2SiMe3)2 {[NNN]=[2-C(H)NDippC6H3NHC(Ph)NDipp], Dipp=2,6-i-Pr2C6H3, Ln=Y (2), Sm (3)}, 2和3通过了1H NMR, 13C NMR, IR和元素分析测试, 通过X-ray确定了化合物2的晶体结构. 加入[Ph3C][B(C6F5)4]和烷基铝, 两个化合物均能高效催化异戊二烯聚合, 具有较好的3,4-选择性(88%), 中等的立体选择性(rr=50%), 较高的分子量(Mn=6.8×104)和较窄的分子量分布(Mw/Mn=1.15). 同时发现, 烷基铝和[Ph3C][B(C6F5)4]的比例影响催化聚合的区域选择性.
高东静 , 胡泓梵 , 崔春明 . 芳基亚胺-脒基稀土烷基化合物的合成及其催化异戊二烯聚合研究[J]. 化学学报, 2013 , 71(08) : 1125 -1128 . DOI: 10.6023/A13040433
Reaction of the arylimine-amidinate ligand[NNN]H (1) ([NNN]=[2-C(H)NDippC6H3NHC(Ph)NDipp], Dipp=2,6-i-Pr2C6H3) with Ln(CH2SiMe3)3(THF)2 (Ln=Y, Sm) in n-hexane at -78℃ followed by stirring the mixture for 3 h at room temperature afforded[NNN]Ln(CH2SiMe3)2 (Ln=Y, 2; Ln=Sm, 3) in 75% and 50% yields after work up. 2 and 3 have been characterized by 1H NMR, 13C NMR, IR spectroscopy, elemental analysis. The molecular structure of 2 has been confirmed by X-ray analysis. Complexes 2 and 3 catalyzed the polymerization of isoprene in the presence of[Ph3C][B(C6F5)4] (1 equiv.) and AlEt3 (10 equiv.) at 25℃. 2 converted 250 equivalents of isoprene into polyisoprene with a narrow molecular weight distribution (Mw/Mn=1.20) and a 3,4-rich microstructure (3,4-selectivity: 78%, rr=50%) in 12 h. A significant increase of 3,4-selectivity was observed in the presence of one equivalent of AlEt3 (3,4-selectivity: 87%). When i-Bu2AlH (10 equiv.) was used instead of AlEt3, the catalytic activity and selectivity did not change noticeably while the resulting polyisoprenes feature a broad molecular weight distribution (Mw/Mn=2.45). When the amounts of i-Bu2AlH decreased from 5 to 1 equivalent, a significant increase of 3,4-selectivity and number-average molecular weight have been observed while the molecular distributions became small. The catalyst is active within a wide range of temperatures from low temperature to 40℃. At 40℃, a similar selectivity (3,4-selectivity: 78%, Mw/Mn=1.43) to that found at 25℃ but the increased reaction rate has been observed. High stereo- and regioselectivity and narrow molecular weight distributions were obtained at -20℃ (3,4-selectivity: 88%, rr=52%, Mw/Mn=1.15). The samarium alkyl 3 exhibited a high activity but low selectivity (25℃, 3 h, 3,4-selectivity: 67%, Mw/Mn=1.71) compared to the yttrium alkyl 2.
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