摘要
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.
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(C6Fs)4] (1 equiv.) and A1Et3 (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 A1Et3 (3,4-selectivity: 87%). When i-Bu2A1H (10 equiv.) was used instead of A1Et3, the catalytic activity and selectivity did not change noticeably while the re- suiting polyisoprenes feature a broad molecular weight distribution (Mw/Mn=2.45). When the amounts of i-Bu2A1H de- creased from 5 to 1 equivalent, a significant increase of 3,4-selectivity and number-average molecular weight have been ob- served 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.
出处
《化学学报》
SCIE
CAS
CSCD
北大核心
2013年第8期1125-1128,共4页
Acta Chimica Sinica
基金
973(No.2012CB821600)资助~~